Vitamin D
Vitamin D excesses
"Oversupplementation or overfortification of foods can result in: •High concentrations of calcium in blood and urine -Deposition of calcium in soft tissues such as blood vessels and kidneys -Cardiovascular damage -Affects function of nervous system -Promotes bone loss •4,000 IUs is Upper Level set by NAS - 5,000 or 10,000 may be safe -No toxicity from sun exposure "
Symptoms of vitamin D deficiency?
"Rickets, Osteomalacia, Osteoporosis •Less calcium absorbed, bone matrix cannot be properly mineralized •In children this results in rickets, -bone deformities and bowed legs •In adults -osteomalacia, a condition of weakened bones -Long term risk for osteoporosis "
Absorption of Vitamin D
"•Dietary Vitamin D3 is absorbed in the small intestine and transported via chylomicrons •Tanning booths- yes (UVB) •Synthesis in skin is blocked by melatonin, sunscreens, air pollution "
Who should take D supplements?
"•Elderly •Northern latitudes •Liver or kidney disease •Fat malabsorption •Others? -People who don't go outside very much? -People with darker skin? "
Metabolism and Storage of Vitamin D
"•Excess stored in liver and fat tissue •Levels and activation has a lot of inter-individual variation •Excretion of vitamin D mainly via bile "
Food Sources of Vitamin D
"•Fatty fish (salmon, herring) -1 Tbsp cod liver oil = 1360 IU -3 oz salmon =447 IU -3 oz tuna fish = 154 IU •Fortified milk (100 IU/ 8 oz) •Some fortified cereal •Liver, beef, eggs •Average intake < 400 IU/day "
Rickets
"•Folklore medicine--Cod liver oil used as preventative •1822 - 1890 Rickets thought to be caused by lack of sunlight •1919 UV radiation cured rickets in children •1921 Rickets improved in children exposed to sunlight on a hospital rooftop •1932 Vitamin D identified •1930s fortification of milk in US "
Vitamin D in Cell Differentiation
"•Movement of vitamin D into nucleus •Vitamin D plus receptor binds to a specific sequence in the DNA (Vitamin D response element) •Regulates the expression of genes coding for specific proteins •More than 900 genes have these elements "
Vitamin D in Other Roles
"•Regulation of gene expression and differentiation -Immune system -Brain and nervous system -Pancreas, skin, muscles, cartilage, reproductive organs, bone, GI tract "
Vitamin D
"•Synthesis from sun exposure •Insufficient sun exposure makes this a vitamin (need to get it via the diet) •Vitamin D is a nonessential (for some) nutrient that acts like a hormone in the body •Derived from cholesterol •Activated by enzymes in liver and kidneys -New evidence activation in other cells as well "
Vitamin D functions
"•Vitamin D in bone growth -Helps to maintain blood levels of calcium and phosphorus -Final activation is regulated by calcium concentrations -Final activation mostly in kidney -Works in combination with other nutrients and hormones -Alters absorption and excretion of calcium •Regulation of blood calcium concentrations "
Is vitamin D an essential nutrient?
"•Vitamin D3 (inactive form) can be manufactured in the skin by the action of sunlight on a molecule derived from cholesterol •Most people, however, require additional vitamin D in the diet •At risk: -People living in cloudy or cold climates -People with dark skin -Elderly"
Vitamin D
calciferol
