When you take a look at the drugstore shelves crowded with vitamin supplies, you’d think that the food supply today is devoid of nutrients. Well, not so: For most people, eating a balanced diet rich in grains, vegetables and fruits, with smaller portions of dairy products and meat, poultry, fish, or beans provides almost all of the vitamins we need.
So why, then, do we buy supplements? Some people – the elderly, for example – may have trouble eating a diet that supplies enough vitamins. Others take high doses of vitamins in hopes of preventing chronic disease. Many are simply seeking dietary insurance. But are supplements really necessary?
All 13 vitamins are, in fact, essential to life. However, only small amounts are needed to regulate your metabolic processes and prevent deficiency diseases, such as rickets (vitamin D), scurvy (vitamin C), and beriberi (vitamin B1). For instance, one glass of orange juice supplies the recommended nutrient intake (RNI) of vitamin C, and even less prevents the scurvy that plagued British sailors centuries ago.
Some research indicates that large doses of some vitamins – larger than those typically found in a healthy diet – can help ward off certain diseases. In other cases, large doses can be toxic. Here are specific examples, according to medical research, of the benefits and risks of taking large doses of vitamins:
This vitamin is known to build bones and teeth. It is needed for calcium absorption, and may reverse or halt osteoporosis and reduce the risk of colon cancer. Taking large doses of vitamin D has no known benefit. On the other hand, taking 2,000 IU or more daily may cause fragile bones, diarrhea, and calcium deposits in the heart, kidneys, and blood vessels.
This vitamin acts as an antioxidant. Taking large doses may help prevent cancer, heart disease, and cataracts and boost immunity. On the other hand, taking more than 1,000 IU daily may increase the risk of bleeding in people taking blood thinners. Taking large doses can likewise cause diarrhea and nausea.
The body converts beta-carotene to vitamin A, and then acts as an antioxidant. Taking large doses may help prevent heart disease, cataracts, and macular degeneration and boost immunity. On the other hand, taking large doses may stain the palm of the hands and soles of the feet orange. For heavy smokers and drinkers, taking large doses may increase their risk of cancer.
This is needed to manufacture DNA and red blood cells. It prevents certain birth defects and may prevent heart disease and cancer. Taking large doses of folic acid has no known benefit. On the other hand, since the safe limit is set at 1,000 micrograms per day, taking larger doses can prevent seizure medication from controlling symptoms and can mask vitamin B12 deficiency.
This vitamin is important for carbohydrate, fat, and protein metabolism. It is needed for red blood cell formation and for proper functioning of the nervous and immune systems. It may reduce risk of heart disease. Taking large doses of vitamin B6 has no known benefit. On the other hand, one study has shown that taking more than 100 mg a day can cause nerve damage in hands and feet, resulting in numbness and problems with walking. Taking large doses can also prevent seizure medication from controlling symptoms.
This vitamin is needed for DNA synthesis, red blood cell formation, proper functioning of the nervous system, and carbohydrate and fat metabolism. It may reduce the risk of heart disease. Some experts recommend 25 mg for older adults who often do not absorb the vitamin from food very well. Taking large doses of vitamin B12 has no known risks in adults.
This vitamin forms collagen, a substance that holds cells together. It speeds wound healing and is needed for proper immune functioning. It helps form neurotransmitters and is important for the metabolism of iron and folic acid. It also acts as an antioxidant. Taking large doses of vitamin C may help prevent heart disease, cancer, and cataracts. On the other hand, taking more than 2,000 mg daily (and for some people, 1,000 mg) may cause diarrhea and nausea. Taking large doses may also produce false negatives in colon cancer tests and false positives in blood-sugar tests. Furthermore, taking large doses of vitamin C may reduce the effect of oral blood thinners.
Many nutritionists believe that supplements are necessary only in specific instances. In fact, if you take them when you don’t need them, or you take too much of a vitamin, you may do yourself more harm than good. Remember, too, that vitamins can interfere with some medications. Check with your doctor before taking them.