The Scientific Scoop on Vitamins

By Dagmar Gross

Vitamins and minerals are essential to our good health. They build immunity against colds and flus, protect the heart, keep our bones strong, and prevent neural tube birth defects. A group of vitamins called "antioxidants" may help fight heart disease and cancer, by preventing "bad" cholesterol (LDL) from attaching to and damaging arteries, and by fighting free radicals, which may injure cells and harm the body's natural healing ability. But which vitamins do we need, and at what levels?

Vitamin C, or ascorbic acid, is an antioxidant that keeps the immune system strong and responsive, and many people faithfully consume large daily quantities to ward off colds. In fact, recent studies indicate that a daily dose of up to 250 mg of vitamin C is sufficient to strengthen the immune system and lower the risk of developing heart disease, cancer or cataracts.^1,2,3 However, smokers require almost double that amount to receive the same benefits.^2,4 Doses of up to 2,000 mg per day of vitamin C appear to be safe and have been shown to reduce allergy and cold symptoms and result in fewer workdays lost due to illness.^2,5,6 One orange contains 70 mg of vitamin C, a cup of cranberry juice provides 108 mg, and a single half-cup serving of broccoli contains 60 mg. Other good sources of vitamin C include lemons, grapefruits, strawberries, peaches, raspberries, red and yellow peppers, tomatoes, cauliflower, Brussels sprouts and baked potatoes.

Vitamin E is another antioxidant that strengthens the immune system and may cut the risk of heart disease. Growing evidence suggests that the optimal daily intake of vitamin E is around 100 mg, or 100 IU.^7,8 But avoid taking high daily doses of vitamin E, since they can depress the immune system,⁹ and excess quantities are stored in the liver. Good sources of vitamin E include vegetable oils, nuts, green leafy vegetables, apricots, peaches, seafood, wheat germ and whole grains.

Beta-carotene, also an antioxidant, benefits the immune system and may protect against some cancers.^10,11 A daily intake of 25,000 IU (or 16 mg) appears to be optimal to strengthen immunity.⁷ However, higher daily doses of 30,000 to 50,000 IU of beta-carotene are shown to raise the risk of cancer in heavy smokers.^12,13 Clearly, the potential dangers of taking large amounts of beta-carotene require further study. Beta-carotene is found primarily in deep yellow-orange and dark green fruits and vegetables, including carrots, spinach, broccoli, tomatoes, squash, sweet potato, pumpkin, beets, papaya, cantaloupe, mango, apricots and watermelon.

Calcium and vitamin D work together to maintain the body and bone mass. Women under 25 require 1,200 mg of calcium daily to maximize their bone mass and reduce the risk of osteoporosis later in life. Adults require about 1,000 mg of calcium per day, but women over 50 not taking estrogen, pregnant women, and women who are breast-feeding need at least 1,500 mg to maintain their bone mass. Calcium is also necessary for the functioning of the brain, lungs, muscles and heart. When calcium intake is insufficient, it is removed from the bones to ensure the rest of the body functions properly. Dairy products such as milk, yogurt, cheese and ice cream are the best sources of calcium, with 300 mg found in a single 8-ounce glass of milk. Other good sources of calcium include spinach, broccoli, canned salmon with the bones, tofu made with calcium sulphate, almonds, brazil nuts and sunflower seeds.

It is equally important to get enough vitamin D, which maintains the blood calcium levels critical for the normal functioning of the other organs. Several studies indicate that we get insufficient vitamin D, particularly in the winter when there is less sunlight, which is required to activate our body's vitamin D.^14,15,16 This deficiency produces rickets in children and accelerates bone loss in adults, which leads to osteoporosis and a greater risk of bone fractures. The data indicates that people under 70 require 400 IU of vitamin D daily, and those over 70 require 600 IU.^14,15 Vitamin D toxicity occurs only if taking more than 2,000 IU a day, for half a year or more, with resulting symptoms of confusion, fatigue, constipation, and possibly kidney stones. A glass of milk contains approximately 100 IU of vitamin D. Some Vitamin D is also found in butter, cottage cheese, carrots, clams, cod livers and cod liver oil, egg yolk, salmon and some cereals.

Finally, folic acid is particularly important for women of child-bearing age. Folic acid deficiencies have been linked to the development of neural tube defects in the fetus, which occur during the first few weeks of pregnancy, before the woman is even aware that she is pregnant. Therefore, it is vital that women ensure they get sufficient folic acid, about 400 micrograms (mcg) a day. Folic acid has also been implicated in the prevention of cancer and heart disease in both men and women.^17,18 Fruits and vegetables, particularly romaine lettuce, spinach, and broccoli are good sources of folic acid.

Copyright © 1997 WOMAN Newsmagazine. Reprinted by permission.

References:

1. Amer J Optimal Nutr 66: 911, 1997

2. Int J Vitam Nutri Res 66:19, 1996

3. Age and Ageing 20:169, 1991

4. Circulation 94:6, 1996

5. Can Med Assoc J 107:503, 1972

6. Scottish Med J 18:3, 1973

7. Lancet 340:1124, 1992

8. J Amer Med Assoc 277:1380, 1997

9. Bogden and Louria, "Micronutrients and Immunity in Older People", in Preventive Nutrition, eds Bendich & Deckelbaum,Totawa, New Jersey: Human Press, 1997

10. J Clin Oncol 8:1715, 1990

11. Nutr Cancer 12:321, 1989

12. New Engl J Med 330:1029, 1994

13. Cancer Res 1;54:2038s, 1994

14. Amer J Clin Nutr 61:1140, 1995

15. Bone and Mineral 25:83, 1994

16. J Clin Endocrin Metab 67:373, 1988

17. Cancer Causes & Controls 7:3, 1996

18. J Amer Med Assoc 274:1049, 1995