THE MICRONUTRIENTS
Vitamins:
• Essential, non-caloric, organic nutrient needed in small amounts in the body
• Although they do not provide energy themselves, they are often regulators of chemical
reactions that involve energy release from the macronutrients
• Structurally, vitamins are individual units rather than long chains of smaller units
Classification
• Fat-Soluble – absorbed with fat, and are stored in the liver and adipose tissue. These vitamins
pose a greater risk of toxicity than water-soluble vitamins.
• Water-Soluble – absorbed into the enterocyte and delivered to the bloodstream. The body
does not store these vitamins in appreciable amounts
The amount of vitamin in a food is dependent upon:
• Soil content
• Growing conditions
• Maturity at harvest
• Food processing
• Storage
Minerals:
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Inorganic elemental atoms or ions
Minerals are not destroyed by heat, light, or alkalinity. They are less susceptible to storage
issues, etc.
Similarly charged minerals can compete for absorption, ex. Ca2+, Mg2+, Fe2+, Zn2+
Classified as major versus trace, based on the amount in the body
Bioavailability – How much of a nutrient do we actually absorb?
Depends Upon:
• Processing of food
• Digestive system
• Other foods eaten at the same time
• Nutritional status
• Source of the nutrient
Deficiency – What causes vitamin or mineral deficiencies?
TWO ways that a deficiency can be caused:
1. Primary: failure to ingest a nutrient in sufficient amounts
2. Secondary: involves failure to absorb or utilize a nutrient after ingestion
PRIMARY: food insecurity, decreased appetite, dieters, exclusion of certain food groups, lack of
education, crop failure
SECONDARY: disease, medication, poor digestion, increased need, other nutrient deficiencies
(ex. Vitamin D)
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WATER and SELECTED MINERALS
The water in body fluids:
• Carries nutrients and waste products throughout the body
• Maintains the structure of large molecules such as proteins and glycogen
• Participates in metabolic reactions
• Aids in regulation of body temperature
• Maintains blood volume and pH balance
• Acts as a lubricant and cushion around joints and inside eyes, and the spinal cord
ELECTROLYTES
• Water in the body contains numerous dissolved minerals, called electrolytes, that are kept in
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constant balance
When salts, such as NaCl, dissolve in water, they break apart into + and – ions
+ = cations (
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- = anions (
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Unlike pure water which conducts electricity poorly, ions dissolved in water carry and
electrical current, hence, they are called electrolytes
Na+ is the major cation in the extracellular fluid, K+ is the predominant cation in the
intracellular fluid
The balance of body fluids and the amount of electrolytes are controlled precisely
In an electrolyte solution, the amount of + charges always equals the amount of negative
charges
Whenever Na+ leaves a cell, other +ions enter (like K+)
Whenever electrolytes move across the cell membrane, water follows
WATER EXCRETION
• Our body loses water through: the skin, lungs, feces (very little), urine
• Depending upon the amount of protein, water, and sodium consumed, we lose 1-2L each day
through the urine
• Insensible water loss accounts for ~ ¼ to ½ of daily fluid loss
• Losses increase in: exercise, high altitude, low humidity, high temperatures, illness (coughing,
fever, rapid breathing, and watery nasal secretions)
Regulation of Fluid Excretion
• The kidneys adjust the amount and concentration of urine in response to the body’s hydration
status
• Low water intake =
• High water intake =
• Osmoreceptors and antidiuretic hormone (ADH) work together to regulate water excretion
THIRST
• Thirst is not always a reliable guide to avoiding dehydration
• Athletes, elderly people, and infants are vulnerable to dehydration
WATER INTAKE RECOMMENDATIONS
• There is no RDA for water
• General recommendation: 1 to 1.5 mL per kcals expended (2400 kcal = 2400 mL or 2.4 litres)
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• Are Americans chronically dehydrated?
WATER SOURCES
• Hydrating beverages: water, milk, fruit juice, herbal tea, most foods (especially fruits and
vegetables)
• Dehydrating beverages: alcohol, caffeinated beverages (coffee, tea, some soft drinks)
DIURETICS
• A diuretic is any substance that increases fluid loss through increased urination
• Alcohol and caffeine act as diuretics by inhibiting ADH activity
• Diuretic drugs are used to help lower blood pressure, decrease intracranial pressure, and
reduce excess pressure in the eye
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What are the effects of chronic dehydration?
Diminished physical performance
Diminished mental performance
Diminished salivary gland function
Increased risk of urinary tract, colon, and breast cancer*
SODIUM
Functions:
Sources:
Deficiency:
Toxicity:
SODIUM and HYPERTENSION
• Our bodies are poorly adapted to handle our modern high sodium, low potassium diets
• About 10-15% of people with hypertension are “salt-sensitive”. If these people decrease their
sodium intake, their BP decreases
• For non “salt-sensitive” people, reducing salt intake has a minimal effect on BP
Other Dietary Factors:
• Excess weight tends to raise BP, exercise and weight loss help to reduce it
• Alcohol consumption can increase BP
• Diets rich in calcium, magnesium, and potassium help to reduce BP
HYPERTENSION (chronic high blood pressure)
• Hypertension injures the artery linings and accelerates plaque formation
• Plaques and reduced blood flow induce a further rise in blood pressure, and HTN and
atherosclerosis become mutually aggravating conditions
• Diagnosis: diastolic pressure >90mmHg and/or systolic pressure >140mmHg (men) and
>160mmHg (women)
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• These values are associated with an increase in mortality of over 50%
POTASSIUM
• Like sodium, potassium is important in regulation of blood pressure, nerve transmission,
muscle contractions, electrolyte balance, and cell integrity
POTASSIUM: Sources
• Good sources include fresh fruits and vegetables, especially bananas, potatoes, spinach,
legumes, squash, and melons. Potassium is lost during processing.
Fresh meat, milk and yogurt, coffee and tea are other good sources
IRON
Functions
OXYGEN TRANSPORT
• Most of the body’s iron is found in two proteins:
• In both, iron helps to accept, carry, and then release oxygen
• Hemoglobin in RBCs transports oxygen to the blood
• Myoglobin facilitates the movement of oxygen into muscle cells
ENZYMES
• Iron is a component of enzymes involved in energy metabolism (cytochromes are hemecontaining compounds in the ETC)
• Iron is also required by enzymes involved in the making of amino acids, collagen, hormones,
and neurotransmitters
• It is also a cofactor for antioxidant enzymes
IMMUNE FUNCTION
• Iron is necessary for optimal immune function
• Iron deficiency decreases concentrations of lymphocytes, natural killer cells, and other
immune factors
• Iron overload can worsen an infection because it serves a nutrient for bacteria
OTHER
• Iron is used by brain cells for normal function at all ages: in the synthesis of neurotransmitters,
and possibly a role in myelinization
• Synthesis of niacin from tryptophan, carnitine synthesis
IRON IN THE BODY
• More than 80% of the body’s functional is found in the RBCs, and the rest is in myoglobin and
enzymes
• The body regulates its iron status by balancing absorption, transport, storage, and losses
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IRON ABSORPTION
Iron absorption in the gastrointestinal tract is the primary regulator of iron levels
It depends upon:
Normal GI function
The amount and kind of iron consumed
Dietary factors that effect iron absorption
• Ferritin receives iron from the GI tract and stores it in the mucosal cells
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• When the body needs iron, ferritin releases some to another protein called mucosal transferrin
• Mucosal transferrin transfers the iron to another protein, transferrin, which transports the iron
to the rest of the body
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Absorption can vary from less than 1% to greater than 50% depending upon:
Body iron stores
Certain conditions – pregnancy, blood loss, menstruation
Gender – men absorb less than women
• Foods contain two types of iron –
• Heme iron is supplied by animal foods which also contain non-heme iron (~40% heme, 60%
non-heme)
• Plant based foods contain only non-heme iron
• Heme iron is 2 to 3 times more absorbable than non-heme iron
• People with severe iron deficiency absorb both heme and non-heme iron more efficiently
Dietary Factors
• Organic acids (like Vitamin C) and meat boost absorption of non-heme iron
• Phytates, polyphenols (found in tea and coffee), oxalates (spinach), calcium and phosphorus,
EDTA (food additive), and fiber inhibit non-heme absorption
IRON TURNOVER and LOSS
• The body recycles iron, and adjusts absorption and excretion as needed
• In adult men, the breakdown of older RBCs supplies ~95% of the iron required to produce
new RBCs
• Adults lose ~1mg per day in the feces, intestinal cells, and skin
• Women require additional iron to compensate for blood loss during menstruation
SOURCES of IRON
• Good sources include beef, clams, oysters, tofu, legumes, and liver
• Fortified cereals provide iron in the American diet
• Foods cooked in iron cookware take up iron salts. The more acidic the food, and the longer it
is cooked, the higher the iron content. However, the absorption may be poor
IRON DEFICIENCY
• Stages of Iron Deficiency: depletion of iron stores – depletion of functional iron – iron
deficiency anemia
• Iron-deficiency anemia is characterized by microcytic, hypochromic RBCs (same as which
vitamin?)
IRON TOXICITY
• Iron poisoning is the leading cause of accidental death in small children
• In a condition called Hemochromatosis, a genetic defect causes excessive iron absorption. Iron
builds up in many parts of the body, leading to severe organ damage and even death
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CALCIUM
Functions
• Bone Structure: as bones begin to form, calcium salts form crystals called hydroxyapatite, on a
matrix of collagen. During mineralization, as the crystals become denser, they give strength
and rigidity to maturing bones
• The calcium in bones serves as a calcium “bank”
• Peak bone mass occurs at ~ 30 years of age
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Nerve function
Blood clotting
Muscle contraction
Cellular metabolism
REGULATION of BLOOD CALCIUM
• Vitamin D
• Parathyroid Hormone
• Calcitonin
CALCIUM: Sources
• Dairy products, blackstrap molasses, canned fish with bones, almonds, sesame seeds, some
dark green leafy vegetables
• Depends on bioavailability:
• >50% absorbed – kale, mustard greens, bok choy, turnip greens, broccoli, calcium-fortified
foods and beverages
• ~30% absorbed – dairy foods, calcium set tofu
• ~20% absorbed – almonds, sesame seeds, pinto beans
• <5% absorbed – swiss chard, spinach, rhubarb
CALCIUM ABSORPTION
• The body normally absorbs 25 to 75% of dietary calcium, depending upon Vitamin D, the
body’s need, and calcium intake
• Calcium absorption is highest during pregnancy and infancy, lowest in old age
• Phytates, high levels of phosphorus and magnesium, and low estrogen levels can decrease
absorption
OSTEOPOROSIS
• Osteoporosis is one of the most prevalent disease of aging, affecting more than 25 million
people in the US – most of then women
• The disease occurs when the bone mineral density becomes so low that the skeleton is unable
to sustain ordinary strains, a condition marked by the occurrence of fractures
BONE BUIDLING NUTRIENTS: calcium, phosphorus, fluoride, magnesium, Vitamin A,
Vitamin D, Vitamin K, potassium (and possibly iron, copper, zinc, manganese, and boron function in bone metabolism, but their roles in preventing bone loss are not well established)
Risk Factors:
• Aging, female sex, limited intake of bone building nutrients, excessive consumption of
potentially damaging substances (alcohol, tobacco), sedentary lifestyle, lack of sunlight,
decreased estrogen levels, genetics, and race
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Dietary Factors
• Excessive dietary fiber may interfere with calcium absorption
• Excessive animal protein consumption may lead to increased urinary calcium excretion
• High sodium intakes, especially in association with low calcium intakes, can result in
increased urinary calcium excretion
• Caffeine can reduce calcium absorption and increase excretion rates
• High phosphorus intake, in association with low calcium intake may increase bone loss
PREVENTION of OSTEOPOROSIS
• Increase intake of bone-building nutrients
• Reduce consumption of alcohol, tobacco, caffeine, sodium, and animal protein
• Engage in regular weight-bearing exercise
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