Vitamin D
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“The sunshine vitamin”
Vitamin D can be made in the skin in response to UV light
BUT particular wavelength of UV light doesn’t get to temperate zone during winter
Persons with dark complexions have to be exposed to summer sun a longer time to
make sufficient vitamin D
Housebound elderly and infants also have lower exposure to light
Influences on Vitamin D synthesis in the skin
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Season
Latitude
Skin color
Environment
Use of sunscreen
Clothing
Age
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Dietary Vitamin D
Requires bile and other fat for absorption
Incorporated into chylomicrons
Transported to liver
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Vitamin D metabolism
In liver, both sources of vitamin D are hydroxylated at 25 position--calcidiol
Calcidiol circulates bound to a vitamin D-binding protein
In response to parathyroid hormone, kidneys 1-hydroxylate calcidiol to calcitriol-active form of vitamin D
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Functions of vitamin D
Increases calcium absorption from the gut
Stimulates bone resorption and formation
May also be involved in enhancing cell differentiation
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Calcium
The most prevalent mineral in the body
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Calcium functions
Structural component of bones and teeth
Needed for nerve and muscle function
Required for blood clotting (remember vitamin K-dependent proteins)
Required for cell metabolism
Normal blood calcium is kept within a very narrow range, with some help from vitamin
D (as calcitriol) and two hormones, parathyroid hormone and calcitonin
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Bone
Where 99% of the body’s calcium is found
Two types of bone
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Cortical--covering surfaces
Trabecular--latticework in interior of bone
Bone is a living breathing tissue
Constantly being resorbed by cells called osteoclasts and osteocytes, and mineralized
by osteoblasts
Osteoblasts secrete collagen, which is mineralized with hydroxyapatite (calcium
phosphate)
Dietary Sources
Vitamin D: Fortified milk, fatty fish, fish oil
Calcium: Dairy products, fortified juice and soy milk, kale, bok choy
DRI’s for Vitamin D & Ca
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Both have AI’s, not RDA’s
Vitamin D: birth to age 50, 5 µg/day; 51-70, 10 µg/day; > 70 15 µg/day
Ca: age 9-18, 1300 mg/day; 19-50, 1000 mg/day; ≥ 51, 1200 mg/day
UL’s: Vitamin D, 50 µg; Ca 2500 mg/day
Vitamin D/Ca/P deficiency
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Rickets in children
– Bowed legs
– “Beading” of ribs
Osteomalacia in adults
– Bone pain
– Bones fracture easily
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Vitamin D Toxicity
Hypercalcemia (too much calcium in blood)
– Kidney stones
– Soft tissue calcification
– Depression
– Nausea, vomiting, anorexia
Phosphorus
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Bone and a whole lot more
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Phosphorus functions
As constituent of hydroxyapatite in bone and teeth
Part of ATP, DNA, RNA
Constituent of phospholipids in membranes and lipoproteins
Phosphorylation can activate or deactivate various enzymes
Dietary Sources of Phosphorus
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Milk
Meats
Nuts
Eggs
Legumes
DRI’s for Phosphorus
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RDA 700 mg/day
Deficiency very rare
UL 3 g/day
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Hyperphosphatemia
Most common in persons with kidney failure
Can result in itching, soft tissue calcification
Sodium
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A mineral worth its salt
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Sodium is…
The predominant extracellular cation
Required for proper nerve and muscle function
Ubiquitous in the typical US diet
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There is no RDA for sodium, but
American Heart Association recommends that we consume at most 2400 mg/day
This is often hard to accomplish, since most processed foods are high in sodium
– Canned soups
– Lunch meat, hot dogs, ham
– Condiments (pickles, olives)
– Chips, crackers, pretzels
Potassium
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The predominant intracellular cation
Sources of Potassium
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Bananas
Potatoes
Dairy products
Orange juice
Tomato juice
Hypo- or hyperkalemia can kill
Hypokalemia results from excess losses coupled with low intake
– Rapid heart rate, weakness, confusion
Hyperkalemia is most often due to kidney failure or excess IV potassium (for example,
when one is being executed by lethal injection)
– Slow heart rate
Nutrition and High Blood Pressure
Still a subject of controversy
What is blood pressure?
A function of how much blood the heart pumps and the resistance offered by the
arteries
Blood pressure is controlled in part by the renin-angiotensin system
Normal blood pressure (BP)
Systolic (upper number) ~ 120
Diastolic (lower number) ~ 80
Ideally should be measured after one has been sitting and relaxed for at least 15
minutes
The lower the BP the better…to a point
– If systolic BP <90, you may be in shock
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What is high blood pressure?
Systolic pressure > 140 and/or diastolic pressure >90
Most people have essential hypertension, which is of unknown cause
Untreated, high BP can lead to stroke, heart attack, and kidney failure
Risk factors for high blood pressure
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Age
Obesity
Diabetes
African Americans
Some people are salt sensitive
All newly diagnosed people with high BP should at least try a moderate sodium
restriction to see if that can bring it down
Many patients are put on diuretics first--increase Na+, water, and (usually) K+
excretion by kidneys
The DASH Diet
• Dietary Approaches to Stop Hypertension
6-9 servings of whole grain products/day
• 10 servings of fruits and vegetables/day
• 2.7 servings of low-fat dairy products/day
• Nuts 2-3 times a week
• Proven to reduce BP in men and women, blacks and whites
• Na+ restriction increases fall in BP