Vitamins A-E, K

Vitamin A through K, where to find them and why they're important
Posted by Brie Zeltner July 14, 2008 08:30AM

Vitamin A: Key to good eyesight. Also important for bone growth and a healthy immune system. Two types, depending on the source--animal or plant. Plant sources, such as orange fruits and veggies and dark-green leafy vegetables, contain carotenoids, a precursor to active vitamin A that the body has a harder time using, but is also less toxic. Vitamin A from animal sources such as liver and that found in fortified foods and the majority of supplements is pre-formed -- already in a usable form -- and can build up to toxic levels much more easily than carotenoids. Most labels tell what percentage of the vitamin is made of beta carotene, or plant sources. The rest is preformed. Most experts recommend no more than 2,300 IU a day for women and 3,000 IU for men.

B Vitamins: B1, B2, B6, B12, niacin, folic acid (the synthetic form of folate), biotin, and pantothenic acid are all important in metabolic activity and in making red blood cells, which carry oxygen throughout the body. B vitamins are water-soluble, so whatever the body doesn't use it gets rid of. Found in whole grains, fish and seafood, leafy green vegetables, dairy products and beans and peas. Current recommendations vary, but it's difficult to end up deficient. Dr. Michael Roizen, chief wellness officer at the Cleveland Clinic, cautions that some studies suggest that high dosages of synthetic folic acid can speed up cancer growth for some people. For others, though, it may help prevent cancer at lower doses.

Vitamin C: Water soluble. Helps form muscle, bone, collagen, and helps the body absorb iron. No conclusive evidence that vitamin C helps fight the common cold, despite many studies. Excess vitamin C is eliminated in urine.

Vitamin D: Known as the sunshine vitamin because your skin makes it when the sun's UV rays shine on you. Critical to the growth and maintenance of strong bones. RDA is 400 IU for most adults, but many researchers think that level is way too low. Many now recommend between 800 and 1,000 IU per day.

Vitamin E: A fat-soluble anti-oxidant. Protects cells against the damage of free radicals. Plays a role in immune function and DNA repair. Found in wheat germ oil, almonds and sunflower seeds, as well as other nuts and vegetables. Current recommendation is 22.5 IU for adults.

Vitamin K: Found in cabbage, cauliflower, spinach and other green leafies. Critical to blood clotting. May help prevent osteoporosis. Deficiency is very rare and is usually caused by an inability to absorb the vitamin. No RDA, but instead an "adequate intake" level because there is no scientific consensus on how much you should get. This level is now set at 90 to 120 micrograms per day. Some multivitamins don't have any vitamin K.