Abstract
Dietary minerals are essential parts of a human diet. Although the most well-known source of
recommended values for dietary minerals are the RDAs, they do not necessarily reflect new research
proposing potential subtle and long-term benefits to extra mineral supplementation beyond the levels in
a normal human diet. Therefore, it is worth examining optimal mineral levels in more details.
Most of the research on dietary minerals is low-quality and probably represents spurious findings.
When these are compared to contradictory evidence and high quality RCTs and meta-analyses are
given preference, only a few minerals continue to show benefits when optimized beyond the level
implicit in a healthy diet. Sodium is widely agreed to cause hypertension, and should be kept as low as
possible, preferably below 1.5g daily. Potassium is protective against hypertension and most diets are
deficient; although supplementation is difficult various dietary strategies are possible to increase it to a
recommended level of 4.7g daily. Women may wish to supplement their iodine intake to 6 mg/day to
prevent breast cancer. Lithium supplementation is still experimental and poorly studied, but the benefits
of a small dose of 1 mg seems worth the risk. Magnesium and selenium are border cases in which the
evidence does not quite support supplementation, but especially interested individuals may wish to read
up on them in more depth. There are minimal projected benefits from optimizing levels of other
minerals.
Recommendations
All minerals as normally obtained from a balanced diet except:
SODIUM: < 1.5 g through dietary control
POTASSIUM: > 4.7g through diet supplemented by potassium salt if necessary
IODINE: + 6 mg supplement for women as Lugol's solution or other molecular iodine
LITHIUM: + 1 mg supplement as lithium orotate
Introduction
The human body is primarily composed of carbon, nitrogen, oxygen and hydrogen, which along with
the much less common sulfur form the major building blocks of large organic molecules like proteins
and carbohydrates. However, some organic molecules and processes require additional elements. About
sixteen elements are absolutely necessary for life [1], but optimal functioning requires several more.
Some of these elements can be obtained from the breakdown of macronutrients; the others must be
obtained separately in the diet and are called the essential dietary minerals.
There is no universal agreement on which dietary minerals are essential. The government's Institute of
Medicine focuses on twelve [2]: calcium, chromium, copper, fluoride, iodine, iron, magnesium,
manganese, molybdenum, phosphorous, selenium, zinc. The Linus Pauling Institute [3], a leader in
nutrition research, adds two others: potassium and sodium. In substance, these lists are identical:
sodium and potassium were excluded from the IoM list only because they were classified as
“electrolytes” rather than minerals, not because of any question as to their importance; these fourteen
are the closest thing to an accepted list. Other sources speculate on the possible importance of
vanadium, arsenic, silicon, and others, but there is as yet no convincing evidence of their importance
[4].
Deficiencies of essential dietary minerals can cause symptoms ranging from subclinical malaise to
serious disease; excess of these minerals can cause various forms of toxicity. As a result, there is
widespread medical interest in the proper dietary levels of these minerals, and in the potential effects of
supplementation. The largest and most rigorous attempt to set these levels is the Institute of Medicine's
Dietary Reference Intakes, most commonly encountered as the RDAs seen on food products. The RDA
of a mineral is defined as the amount which should “meet the nutrient requirement of 97-98% of
healthy individuals in a particular life stage and gender group.” [4]. Researchers can use multiple
different methods to calculate an RDA.
In some cases, researchers calculate an RDA by examining the amount of the mineral lost each day in
urine, sweat, et cetera, and choosing a value that is most likely to produce a neutral mineral balance in
the body. In others, they compare dietary intake of a mineral to some clinical reference value affected
by the mineral: for example, since dietary potassium affects the levels of serum potassium, they
determine what levels of dietary potassium are most likely to cause a healthy level of serum potassium;
here healthy values of serum potassium have already been set by previous studies, since serum
potassium is much easier to measure than dietary intake. In still other cases, they will measure the
activity of an enzyme that depends on the mineral; for example, the RDA of selenium is based on the
amount needed to bring activity of the selenium-based glutathione peroxidase enzyme to its plateau
value [5]. In the most robust RDAs, researchers test several or all of these methods and establish a
value only when they find them to be broadly in agreement.
In cases where an RDA cannot be established, researchers determine an AI, or Adequate Intake. AIs
usually represent a level equal to or somewhat higher than the average observed among a population
who eat a balanced diet and show no clear signs of mineral deficiency.
Finally, the Dietary Reference Intakes often include a Tolerable Upper Intake Level, "the highest level
of daily nutrient intake that is likely to pose no risk of adverse health effects for almost all individuals
in the general population". [4]. In the best cases, these levels are obtained after having observed the
level of adverse effects at different levels of intake. In cases where such data is not available, they may
be obtained through animal models or through measurement of mineral accumulation in the body.
The Dietary Reference Intakes set the gold standard for recommended quantities of essential minerals
in the diet, but they have only the very modest goals of avoiding overt clinical deficiencies. Recent
medical research has included several startling claims that extra supplementation of minerals beyond
the levels necessary to meet the DRIs has unexpected positive effects, including the prevention of
cancer and cardiovascular disease. These claims generally remain controversial, but if true would imply
a benefit to mineral intake in excess of the DRIs and other commonly used guidelines. This necessitates
a closer examination of the costs and benefits of each.
This analysis will begin with the DRIs for each mineral, with special emphasis on whether the average
Western diet can be expected to satisfy those values. It will continue to discussion on proposed benefits
of an intake above (or in some cases like sodium, below) the DRI, and whether or not the evidence for
these proposed benefits reach statistical and clinical significance. Finally, if it determines that there is a
clinically significant positive effect of an intake level significantly above or below the level commonly
encountered in the diet, it will conclude with a discussion of whether supplementation is cost-effective
and whether it poses any potential risks of its own.
To some degree, examining the cost-effectiveness of mineral supplementation a purely academic
exercise. Many people who supplement their diet do so through a multivitamin containing multiple
minerals. This makes an analysis of the dollar cost per life saved of, for example, selenium versus zinc
supplementation somewhat moot; most people would be buying neither selenium pills nor zinc pills,
but a multivitamin containing both. Examining the costs and benefits of multivitamins might prove a
more practical exercise, but contains its own pitfalls: a multivitamin might contain both helpful and
harmful substances. This is further complicated by the consistent failure of studies to show any benefit
whatsoever from multivitamins [6, 7]. Because of these limitations, this analysis will discuss costeffectiveness recommendations on the basis of individual minerals, while keeping in mind that this may
overstate the financial costs relative to those of a multivitamin.
This analysis suffers from several potential limitations. First and foremost is the confused state of most
evidence relating to the benefits of dietary minerals. This confusion is in most cases due not to an
absence of studies, but to a profusion of studies with contradictory results. Where possible, this analysis
has tried to examine the largest studies or systematic reviews or meta-analyses of all studies. It has also
relied heavily upon the judgment of the Cochrane Collaboration, widely considered the world leader in
meta-analysis
A more fundamental limitation is the limits of quantifiability itself. Some minerals may make people
feel healthier, give them more energy, or improve their mood. Although this is quantifiable in principle,
and in some cases even relates to easily quantifiable end points like depression diagnoses or suicide, in
general very little research has been done in the area and that which has been done is hard to trust.
Therefore, this analysis focuses on more easily quantifiable end points such as health maintenance and
disease prevention.
Calcium
The AI of calcium for adults age 19-50 is 1000 mg; the TUL is 2500 mg. This number was set because
it was between the 50th and 75th percentile of calcium intake in healthy men, and the 90th and 95th
percentile of calcium intake in healthy women. [8]; it also approximates the intake necessary to achieve
a calcium balance supporting normal bone accretion.
Mean calcium intake in the United States is 871 to 1,266 mg/day in men and 748 to 968 mg/day in
women; although the diets of children and the elderly are often deficient in calcium, most adults 19-50
consume around the AI or above. [8, 9]
Proponents of calcium supplementation point to studies suggesting it may decrease the risk of
osteoporosis and colon cancer later in life as well as treat hypertension. Indeed, one recent
observational study suggested that calcium could decrease all-cause mortality [10], though the study's
own authors cautioned against taking this correlational evidence too seriously. However, other studies
suggest calcium can increase the risk of cardiovascular disease and prostate cancer.
Calcium prevents osteoporosis. When combined with Vitamin D, calcium supplements can decrease
fracture risk in elderly populations by up to 40%; this effect is greater than that of Vitamin D alone .
Premenopausal women and younger men are at low osteoporotic fracture risk. [11]
Calcium probably prevents colon cancer [12]. In the Calcium Polyp Prevention Study, subjects who
took a 1200 mg calcium supplement daily cut their risk of adenoma, a precursor of colon cancer, by a
statistically significant 15%. But a subsequent study, while confirming the finding, found that extra
calcium beyond the first 700 mg daily had no added protective effect [13], implying no benefit to
amounts of calcium beyond those common in an average diet.
Some studies have found an inverse relationship between calcium intake and hypertension. For
example, in the Women's Health Study, those in the highest quintile of calcium intake had a relative
hypertension risk of only .89 that of those in the lowest quintile. [14]. However, subsequent studies and
meta-analyses have failed to confirm this finding. The Cochrane Review on Calcium Hypertension
analyzed 13 RCTs and found a small but statistically significant effect of calcium supplementation on
systolic blood pressure of -2.5 mm Hg, and no significant effect on diastolic pressure. However, many
of the studies involved were poor quality and inadequately blinded, and the meta-analysis concluded
that "due to poor quality of included trials and heterogeneity between trials, the evidence in favour of
causal association between calcium supplementation and blood pressure reduction is weak and is
probably due to bias." [15]
Some studies have found increased health risks from calcium supplementation. In particular, an RCT
associated with the Women's Health Initiative found calcium supplements increased the risk of heart
attack and stroke by about 20% each [16]. These results are difficult, since calcium is often taken along
with Vitamin D and there are complex interactions between the two. A model in which calcium
increases the risk of cardiovascular disease but Vitamin D decreases this effect is both biologically
plausible and empirically supported [17]. High calcium diets may increase the risk of prostate cancer.
High serum calcium levels can triple prostate cancer risks [18] and a meta-analysis of twelve
observational studies found that both dairy consumption and calcium consumption were significantly
linked to prostate cancer, with relative risks of 1.11 and 1.39 respectively [19]. Finally, high calcium
can increase the risk of kidney stones, constipation, and the neurological symptoms of hypercalcaemia.
Although calcium intake during youth can build up bone stores that prevent osteoporosis when
younger, these effects seem less pronounced than its possible risks Calcium's effect on hypertension is
unclear and possibly nonexistent. Although it probably does prevent colon cancer, calcium levels above
those in an average American diet do not have extra protective effect. High calcium intake probably
increases the risk of prostate cancer and may increase the risk of heart disease, as well as many
medically well-recognized acute symptoms such as kidney stones and digestive complaints. Therefore,
healthy adults below the age of fifty who are not at unusually high risk for osteoporosis should aim for
a diet including the recommended 1000 mg/day of calcium, but should generally avoid calcium
supplements.
Those people who do choose to take calcium supplements should take Vitamin D as well. Calcium
carbonate is relatively safe and effective except for those who use PPIS, H2 blockers, or have other
drugs or conditions decreasing the normal levels of stomach acid; these people may experience fewer
digestive effects with calcium citrate. [11].
Chromium
The AI of chromium for adults age 19-50 is 35 micrograms/day for men and 25 for women; there is no
TUL because chromium is not known to have any toxic effects. The AI was set by examining 22 wellbalanced adult diets and choosing the one with the highest levels of chromium to adjust for likely
under-reporting. [5]
The average American adult chromium intake is 33 micrograms/day for men and 25 for women [20],
although some analyses suggest it may be higher [21]. These numbers are relatively close to the AI and
signs of chromium deficiency are extremely rare.
Because chromium potentiates the effects of insulin, there has been widespread interest in its use in
metabolic conditions such as obesity and diabetes. Pittler et al [22] found evidence of a statistically
significant weight loss of about 0.1 kg per week with chromium picolinate supplementation. Three
problems mar this result; first, this rate of weight loss is not clinically significant (compare to diets,
which can burn 0.5 to 1 kg per week) unless maintained over long periods, and none of the studies in
the analysis had a follow-up of more than a few months. Second, the meta-analysis found heterogenous
results, with most of the positive findings being sponsored by manufacturers of chromium supplements.
Third, an associated funnel plot shows evidence of publication bias. More recent meta-analyses fail to
replicate the positive result and find no effect of supplementation [23].
Because chromium potentiates the action of insulin, and type II diabetes is primarily a disease of
insulin resistance, there has been interest in the ability of chromium to prevent or reverse diabetes.
However, most studies have failed to show an effect of chromium supplementation on glucose control;
the only outlier was a study from China which found the supplementation with 1 mg of chromium per
day decreased serum glucose by 15-19% in Chinese diabetics. Critics of the study say that results from
a Chinese population who are much less obese than American diabetics and who may be chromium
deficient to begin with do not generalize well to the western world. [24]. Other studies in diabetics
found chromium increased weight gain when taken in conjunction with the sulfonylureas, a commonly
prescribed group of antidiabetic drugs. [25] Chromium does not appear to prevent diabetes or decrease
weight gain in non-diabetics. [26].
Some case studies have suggested idiosyncratic side effects of chromium supplementation including
rhabdomyolysis (a dangerous form of muscle breakdown) and exanthematous pustulosis (a form of
rash), but these have not been verified.
The evidence that chromium helps people lose weight is shaky, and even if true the effect is probably
minimal. Chromium may improve glycemic control in diabetics. but does not itself prevent diabetes.
Healthy adults do not need chromium supplementation; there is too little evidence to recommend for or
against such supplementation in diabetics, although those who use sulfonylureas may wish to be
especially cautious. Chromium picolinate is the most bioavailable form of chromium and probably the
preferred form for supplementation.
Copper
The RDA of copper for adults is 900 mcg, based on serum copper and ceruloplasmin concentration,
superoxide dismutase activity, and platelet concentration. The TUL of 10 mg/day is based on fears of
liver damage, but this has never actually been observed at any copper intake in healthy people. [5]
The average US intake according to NHANES II is 1700 mcg/day, well above the RDA. No groups are
at significant risk of copper deficiency. [27] Although copper in vitro acts as an oxidant, studies in
humans have not shown strong effects. A few studies have shown positive effects of copper on
cholesterol balance and osteoporosis [28], but subsequent studies fail to confirm the result [29] and
epidemiological studies on heart disease are contradictory, finding either weak positive effects or weak
negative effects [30, 31].
Because of contradictory epidemiological studies and the lack of robust RCTs, there is no strong
evidence for optimizing copper intake beyond simply eating a balanced diet.
Fluoride
The AI of fluoride for healthy adults is 3.8 mg per day for men and 3.1 for women, based on the levels
found to most effectively prevent dental caries, and the TUL is 10 mg per day based on a level known
not to cause skeleton fluorosis (lower levels may have adverse effects in children).
The average US fluoride intake is 1.8 mg per day from food and perhaps the same amount from
fluoridated water [32], for a total of about 4 mg.
Fluoride is undoubtedly effective in preventing dental caries. Although most of the evidence concerns
children [33], a 2007 meta-analysis found that exposure to fluoride in water or dental products
decreased cavities by 27% [34]. Although there is some risk of dental fluorosis in younger children this
risk disappears by about age eight; skeletal fluorosis could theoretically affect adults but has not been
observed to cause any effects at normal doses [35].
Healthy adults should aim for fluoride's AI of 3.8 mg; as long as they live in a community with
fluoridated water this should not require additional effort. People living in communities with nonfluoridated water may wish to consider fluoridated dental products instead of increasing dietary
fluoride intake.
Iodine
The RDA of iodine for adults age 19-50 is 150 micrograms/day; the TUL is 1100 micrograms. The
RDA was set by examining iodine turnover in the thyroid and excretion in the urine; the TUL was set
by examining the intake at which thyrotropin levels rises, indicating potential subclinical
hypothyroidism. The median American daily iodine intake is about 250 micrograms per day for men
and 200 for women, well above the RDA, mostly due to consumption of iodized salt. [5] Ironically, the
otherwise good advice to limit salt intake may be increasing the incidence of iodine deficiency, which
has quadrupled over the last twenty years to 11.7% of Americans [36].
Iodine is best known for its effects on the thyroid, but as mentioned above these plateau around the
RDA, and there is no evidence that more iodine improves thyroid function further. More interesting are
a series of studies on iodine and breast disease. Low iodine level increases the likelihood of ductal
atypia progressing to ductal carcinoma, a form of breast cancer. [37, 38]. This may explain why the
Japanese, whose diet can include 10mg daily iodine or above, also have some of the world's lowest
breast cancer rates. [39] . In addition, one large observational study in Finland found a strong negative
correlation between iodine intake and cardiovascular disease; the results are interesting but have yet to
be followed up [36].
The iodine levels found to be protective against breast disease, commonly around 6 mg [40], are well in
excess of the TUL. However, the TUL was set to prevent any detectable rise in thyrotropin; most rises
in thyrotropin will not be associated with clinical symptoms of hypothyroidism, and any symptoms
experienced will be mild and reversible with return to a normal-iodine diet. The Japanese, who
consume a seafood and seaweed-rich diet, maintain an iodine intake from 10 to as high as 45mg daily
without apparent health effect [39].
Although the cardiovascular benefits are unproven, iodine's preventative potential in breast cancer
seems sufficiently well grounded to support iodine supplementation in women. The evidence supports
6mg of iodine daily as a level that will minimize risk of breast cancer while being unlikely to have
toxic effects despite the official TUL; anyone beginning such a program of iodine supplementation
should consider contacting their doctor to discuss monitoring thyroid function. Men are at much lower
risk of breast cancer and would gain few benefits from iodine supplements.
Iodine supplementation can be further optimized by taking it in the form of molecular iodine; this form
may be preferentially absorbed by the breast, as opposed to potassium iodine which is preferentially
absorbed by the thyroid. [39].
Iron
The adult RDA of iron is 8mg per day for men and 18mg for women, based on estimating losses. The
TUL is 45mg per day, based on the level needed to cause gastrointestinal complaints. The average man
consumes 16mg iron daily; the average woman 12. [5]
Iron is most important as a component of hemoglobin; iron deficiency causes anemia, most frequently
presenting as feeling "tired all the time". Groups at risk for iron-deficiency anaemia include
vegetarians, pregnant women, and women who menstruate heavily; it can be diagnosed by a simple
blood test. There are no advantages to taking more iron than is necessary to replace losses and prevent
anemia.
Individuals should try to reach their RDA of 8-18 mg iron per day. People at special risk of deficiency
such as menstruating women and vegetarians should consider supplementation; any iron-containing
multivitamin will work. Because iron overload can cause serious complications including cancer, heart
disease and possibly neurological diseases [41], individuals should consult their doctors before
beginning iron supplementation.
Magnesium
The RDA for magnesium is 420 mg for men and 320 for women, based on levels needed to maintain
magnesium balance. The TUL is 360 mg, set to minimize risks of magnesium-induced diarrhea, but it
only applies to magnesium obtained through non-food sources such as supplements. [8]
The CSFII study found the average American diet to contain 323mg per day in men and 228 in women,
levels which were broadly confirmed by the NHANES study. Most diets are therefore slightly
magnesium deficient [27].
Magnesium has been credited with reducing hypertension, improving glycemic control, preventing
cardiovascular disease; however, most comes from observational studies only, or is otherwise
untrustworthy. Because magnesium is found in fruits and vegetables, observational studies that show
good outcomes from high magnesium (see for example [42]) are probably only capturing the effects of
a generally healthy diet.
The large ARIC study found only marginal effects of serum magnesium on blood pressure, and no
effect of dietary magnesium intake. [43] Some prospective studies have found magnesium to prevent
heart disease [44] but others have not [45]. The latter study seems more believable, as the former found
an effect in women but not men, and only when testing an overall trend rather than quartile by quartile,
suggesting possible overtesting.
There is some RCT support for magnesium as a treatment for diabetes [46] and migraines [47]; IV but
not oral magnesium probably helps asthma [48].
Magnesium can improve cognitive functions in rats even when the rats have what appears to be a
normal magnesium diet [49], but normal magnesium supplements are not neuroavailable; the study
used a customized supplement of magnesium-l-threonate. This effects have never been tested in
humans.
Magnesium alone probably does not prevent hypertension or heart disease, but high magnesium is part
of a balanced diet. Although there is not sufficient evidence to support magnesium supplementation,
working towards a diet with the recommended 320-420 mg magnesium will probably improve health
regardless of magnesium's particular role; such a diet would also avoid the potential gastric side effects
of magnesium supplements. If an individual cannot maintain such a diet, supplementation with about
100 mg magnesium is a not entirely unreasonable strategy, albeit not one with unambiguous evidence
behind it. Bioavailability studies show a slight advantage of magnesium chloride and lactate based
supplements over magnesium oxide; anyone interested in testing cognitive effects should choose a
neuroavailable version like magnesium-l-threonate. [50]
Manganese
The AI for manganese is 2.3 mg/day for men and 1.8 for women; these levels have been corroborated
by balance studies. The TUL is 11 mg/day, based on a serious risk of neurotoxicity leading to
Parkinsonian symptoms. [5]
The average American manganese intake is 3.4 mg/day in men and 2.7 in women, well above the RDA.
There are no known cases of manganese deficiency in healthy humans [51].
Like many other nutrients, manganese is part of a balanced healthy diet, and so observational studies
are likely to find relationships between manganese levels and various positive health outcomes; among
results most likely explicable in this way are its apparent relation to diabetes [52, 53], which did not
hold up in RCTs [54].
Although some manufacturers of manganese supplements suggest the mineral has beneficial cognitive
and emotional properties [55], the evidence says otherwise: high levels of manganese in water are
associated with a 6.6 point IQ decrease in children [56] and increased childhood irritability [57]. Adult
data is less readily available.
Because of the high potential for manganese toxicity, and continuining uncertainty over possible cover
toxicity of relatively low manganese levels, manganese supplementation is probably a bad idea. As
usual, a balanced diet that naturally achieves the AI is the best strategy.
Molybdenum
The RDA of molybdenum is 45 micrograms/day, based primarily on balance studies. The TUL is 2
mg/day based on kidney failure in rats, but direct applicability to humans is unlikely [5].
Different studies have set the average daily intake at 180 micrograms [58] and around 100 micrograms
[59].
There are few claims of any particular beneficial effects of molybdenum supplementation, and
deficiency is rare. There is not enough evidence to recommend molybdenum optimization beyond
levels available in a balanced diet.
Phosphorous
The RDA of phosphorus is 700mg/day, based on maintenance of safe serum phosphorus levels. The
TUL is 4g per day, based on theoretical models and animal studies suggesting phosphorus can change
calcium balance and calcification, but in practice no study has directly detected these effects in humans.
The average intake of phosphorus is 1500 mg in males and 1024 mg in women [8]; nearly everyone
exceeds the RDA primarily because of phosphorus in processed foods.
Nutritionally, phosphorus is usually viewed as a potential danger, as exemplified by warnings about
phosphoric acid in soda. However, studies have failed to confirm this danger. Despite worries about
calcium:phosphorus ratios, even extremely low Ca:P ratios failed to produce detectable effects [60].
Some animal experiments showed skeletal lesions in rabbits on a very-high-phosphorus diet, but these
required around forty times the phosphorus levels even the most prolific soda-drinker could expect
[61]. Likewise, metastatic calcification (which despite its name is not a cancerous process but only the
abnormal deposition of calcium in tissue) does indeed seem linked to high serum phosphorus, but at
levels only attainable by disease processes; even dietary phosphorus intakes above the 95th percentile
have never been observed to favor such a process [8].
Although "phosphoric acid" sounds sinister, the amount of phosphorus in soda is relatively small, and
although some observational studies do show negative effects of soda on bone health, this could
equally likely represent soda replacing healthier calcium-rich beverages like milk, or a general
correlation between excessive soda use and an unhealthy diet [62].
Drinking large quantities of soda is probably unhealthy for very many reasons, but excess phosphorus
is probably not one of them. Healthy individuals probably have no reason to try to optimize their
phosphorus intake beyond eating a well-balanced diet.
Potassium
The AI of potassium for adults age 19-50 is 4.7g, which was set at the level found to most effectively
decrease blood pressure and risk of kidney stones. The kidneys regulate potassium balance tightly
enough to prevent overload in healthy people, and so there is no TUL. [63]
There is a robust evidence base for the efficacy of potassium in reducing blood pressure. A Cochrane
meta-analysis of six RCTs found a statistically nonsignificant decrease in systolic blood pressure of 3.9
mm Hg, and in diastolic blood pressure of 1.5 mm Hg upon potassium suppelementation, although
results were inconsistent and the authors suggest cautious interpretation of the results [64]. There was
no advantage in supplementation of >4g over supplementation of less than that amount. A different
meta-analysis of 33 studies found that potassium supplements of between 2.3 and 3.9g per day
decreased blood pressure by a statistically significant level of 1.8/1 in normotensive and 4.4/2.5 in
hypertensive subjects. [65].
A meta-analysis by the College of Cardiology containing a total of 247510 subjects found that subjects
with a high-potassium diet, on average 1.64g higher than those with low-potassium diets, had a 21%
lower risk of stroke, although this was an observational study and may show nothing more than that
people who eat more fruits and vegetables, and therefore more potassium, are more healthy in general
[66]
All these studies broadly agree with the DRI's AI, a 4.7g figure which would require an extra 2.5g per
day over normal dietary intake. Therefore, potassium supplementation is advised for both men and
women. Unfortunately, potassium supplements are not widely available; the FDA bans supplements
with more than 55mg potassium because of their potential danger to renal patients [63]. Alternative
methods of increasing dietary potassium include a balanced diet with more fruits and vegetables (most
famously bananas) or liberal use of potassium-based salt (which has the added advantage of cutting
down on unhealthy sodium-based salts). People on long-term medications or with renal disease should
talk to their doctor before trying to increase the potassium in their diet.
Selenium
The RDA of selenium for both men and women is 55 micrograms per day, a number set by examining
the activity plateau of the selenium-dependent glutathione peroxidase enzyme. The TUL is 400
micrograms per day, set upon derivation of likely selenium intake for five patients with selenium
poisoning leading to hair and nail loss. [5]
Different studies have found the average American diet to contain 81 [67] to 87 [68] micrograms
selenium per day. No overt symptoms of selenium deficiency or excess have ever been observed in
healthy American adults.
Selenium is a cofactor for the reduction of antioxidant enzymes. Many claims have been made that
antioxidants help fight cancer, heart disease, and even normal aging, but the most complete
investigation of these claims, a Cochrane meta-analysis of 67 studies and over 200,000 individuals,
contradicts these claims and found no significant effect of antioxidant supplementation on mortality
[69].
Somewhat more plausible are claims that selenium helps prevent cancer. Selenium supplementation
consistently lowers cancer risk in small animal models [70]. Low selenium and cancer have also been
correlated in several observational studies on humans, but this may be an effect of class; wealthy
people have higher selenium intakes and are less likely to develop cancer. However, some RCTs have
also found an effect; the NPCT found a significant 37% decrease in cancer incidence and 50% decrease
in cancer mortality over 1312 subjects after supplementation with 200 micrograms selenium. [71]
However, further studies have failed to confirm this finding. The SELECT study of 35,534 men
analyzed prostate cancer, one of the cancers most affected in NPCT, but found no statistically
significant effect from the same 200 microgram dose. [72]. A Cochrane review of six RCTs concluded
that “the trials with the most reliable results found that organic selenium did not prevent prostate cancer
in men and increased the risk of non-melanoma skin cancer in women and men. Other trials found that
participants using selenium salt or organic supplements had a decrease in liver cancer cases. However,
due to methodological shortcomings this evidence was less convincing.”
Although there are many studies on both sides, most experimental studies, especially the largest, find
no benefit of selenium supplementation in prevention of prostate cancer or any other type of cancer;
some find increases in non-melanoma skin cancer, in prostate cancer [72], or a dose-dependent
relationship in which all cancers increase at selenium intakes greater than 150 micrograms per day [73].
Therefore, selenium supplementation cannot be recommended at the present time [74]. This is
especially true of supplementation in the form of selenium-containing multivitamins, which are
advertised as preventing prostate cancer but actually increase risk of prostate cancer slightly. [6].
Individuals should continue to aim for the RDA of 55 micrograms per day selenium unless they have
specific medical reasons for doing otherwise.
Sodium
The AI for sodium is 1.5g/day, but the DRI admits that people can survive and thrive on sodium intakes
less than .2g per day, and that the higher recommendation is only to “ensure that the overall diet
provides an adequate intake of other important nutrients and to cover sodium sweat losses in
unacclimatized individuals." The TUL is 2.3g, selected primarily because it "was ... the next level
above the AI that was tested" but the detrimental effects of sodium seem gradual and mostly linear,
making a true cutoff difficult. [63]
The average American diet includes 3.1-4.7g sodium for men and 2.3 to 3.1g for women from food, but
this does not include table salt and so probably underestimates the real amount. [27].
The INTERSALT study [75] confirmed the now universally accepted idea that sodium intake is linked
to high blood pressure, a risk factor for heart attack and stroke. The DASH-Sodium study found that
restricting sodium to 1500 mg sodium/day diet decreased blood pressure by 5.6/2.8 mm Hg [76].
The literature on sodium and hypertension supports a recommendation to limit sodium as far as
possible. The strongest evidence base supports positive effects of sodium limitation at least down to
1500 mg/day; limiting it further may reduce blood pressure even more but is probably not practical in a
modern diet.
Zinc
The RDA of zinc is 11mg/day for men and 8mg/day for women, based on zinc balance studies and the
activity of the the copper-zinc superoxide dismutase enzyme. The TUL is 40 mg/day, again based on
the best range for enzyme activity.
The average American diet includes 14mg/day zinc in men and 9mg/day in women, slightly above the
RDA; 16 percent also supplement this with zinc-containing vitamins. [4] Zinc deficiency is relatively
rare among healthy adults in developed countries, although it is sometimes suffered by vegetarians,
who consumed high levels of bioavailability-decreasing phytic acid [77]
Although zinc is well-known for purported benefits against disease processes from the common cold to
HIV/AIDS, there are relatively few and modest claims of benefits in healthy people. One study
suggested a role against macular degeneration [78], but it was poorly conducted, ran too many tests,
and only achieved a marginally significant result [79]; subsequent studies have found no effect [80].
There is little evidence for zinc supplementation in healthy people. Vegetarians who expect their diet to
be deficient in zinc may wish to supplement; there are few reasons to prefer any form of zinc
supplement over another [4].
Other nonessential minerals
Lithium is not often considered an essential mineral, but deficiency studies show effects ranging from
low litter size in rats to behavioral abnormalities in humans [LITHIUM_1]. There is no federally
established RDA or TUL for lithium; an unofficial TUL is 100 mg. The average intake is around 650
micrograms.
The doses of lithium used medically to eg treat bipolar disorder, usually 100 mg/day or above, are
potentially highly toxic and must be monitored by medical professionals to prevent heart, kidney, and
other forms of damage. However, much smaller doses of lithium are found in drinking water, and seem
to have several positive effects. An observational study in Japan found high lithium levels in drinking
water (with tested levels ranging from .7 to 59 micrograms/liter) to significantly decrease all cause
mortality (p = .003); a followup experiment with nematodes found lithium supplementation could
increase nematode lifespan by 4-36% [81,82]. Even more interesting is a study from Texas
municipalities with lithium levels in drinking water ranging from negligable to 170 micrograms/liter;
individuals in high-lithium cities side had fewer crimes, suicides, and drug addictions (p < .01). [83]
These water levels would correspond to about 340 micrograms/day extra lithium. In the laboratory,
positive effects have been found with lithium supplementation of as little as 400 micrograms [84].
It seems plausible that supplementation of around 1 mg lithium per day could have significant positive
benefits, while not reaching the levels necessary for toxicity. Certainly this level would be
recommended for people with subclinical mood problems or psychiatric problems. Lithium citrate or
carbonate of the sort used in bipolar disorder is not available over the counter, but lithium orotate
supplements are. Taking doses of lithium larger than the upper end of the natural distribution, even as
low as 5 mg, could be dangerous and should be discussed with a doctor.
Analysis
The statistical value of a year of human life is commonly set around $100,000; supplementation of
some dietary minerals may save lives. This possibility must be weighed against the costs of taking that
supplement, both financial and in terms of annoyance. Many supplements cost around the range of
$25/year; they may take a few hours to obtain, taste unpleasant, and cause some minor side effects like
stomach upset: we will arbitrarily decide these additional costs are worth about another $25. An
average individual may take the supplement for about fifty years, from the time they become an
adult to old age. In this model, the lifetime cost of the supplement is $2500, and the individual
should take the supplement if they believe there to be greater than a 1/40 chance it will save at
least a year of life.
Most potentially preventable diseases occur around the end of life. Taking cancer and heart disease as
two prototypical examples, the average age for a first heart attack is 68 [85] and the average age of a
cancer diagnosis is 67 [86]. The average US life expectancy is 78 years [87]. The "natural" conclusion
that preventing one episode of cancer or heart disease therefore potentially saves ten years is probably
an overestimate; people who get cancer or heart disease are probably in general less healthy, and not
every episode prevented will be the first episode; suppose then that preventing one episode of serious
disease potentially saves five years.
The death rate from heart attack is 38%; the five-year death rate from all cancers averaged 50% [88].
So although preventing one episode of serious disease potentially saves five years, it actually saves
only half of that, because half the patients would survive.
If a year is worth $100,000, successful supplementation saves 2.5 years, and supplementation costs
$2,500, this suggests that a supplement is valuable if it has a 1/100 chance of successfully preventing
one episode of serious disease if taken over a lifetime. This number is inadequate for many reasons: it
excludes the benefits of preventing nonfatal illnesses, it excludes the possibility that a supplement may
have side effects and so have negative value, and, of course, it is only an extremely rough estimate.
Taken as a rough estimate, however, it provides a bar for these mineral supplements to pass: they
should have a 1% chance of preventing a serious disease, or be equally valuable in some other way.
Several supplements reach this bar. As mentioned above, potassium supplementation decreases systolic
blood pressure by 2-4 points. Although the exact point-by-point relationship between hypertension and
cardiovascular disease depends on several factors, most people could decrease heart disease risk by
50% with a 10 point drop in blood pressure [89], suggesting that potassium's 2-4 point drop well
exceeds the 1% threshold even before other hypertensive diseases such as stroke are factored in. Low
sodium diets, which have even greater effects on blood pressure, similarly pass this bar.
Although iodine probably has a protective effect against breast cancer, it is hard to quantify exactly
what it is. The number 50% comes up often: first as 50% decrease in breast pain from a precursor
condition to breast cancer [90] and second as the amount breast cancer declined in an unpublished
study that seems somewhat questionable [39]. More likely the number is much lower, but even at a
tenth of this level it would still pass the 1% threshold.
Lithium is the most poorly-researched and most uncertain of all the minerals in this analysis. It
improved lifespan 4-36% in nematodes, but is unlikely to be anywhere near as effective in humans.
Further, much of its effect would probably be on mood and psychological well-being, which would
operate independently of concerns about lifespan. Nevertheless, its low cost (under $20/year) makes it
a reasonable option.
Other dietary minerals do not seem to have any quantifiable benefits at levels beyond those in a normal
diet.
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