By Eduardo Gonzales, MD
I read a news article that says a scientific study has shown that high doses of vitamin B supplements increases one’s risk for cancer. Can you comment on this? —firstname.lastname@example.org
The study you’re talking about was by Theodore Brasky, an epidemiologist in the division of cancer prevention and control at the Ohio State University College of Medicine. His work showed that men who took high doses of vitamin B6 and B12 supplements had a 30 percent to 40 percent increased risk of lung cancer, and the association was highest among current smokers.
Brasky’s is simply an initial study and can’t be considered enough proof that these high-dose supplements cause cancer, but it is certainly another argument against multivitamin supplements.
Normal adults don’t need vitamin supplements
Vitamins are compounds that are needed by our body for normal health, growth, development, and reproduction. Their absence is not compatible with life and their deficiency results in illness. But we need vitamins in minute amounts only. A balanced diet is enough to provide all the vitamins we need.
Yet, in the last couple of decades, more and more people worldwide have embraced the habit of taking multivitamins in high doses on a regular basis because they supposedly boost energy, delay aging, and provide protection against a host of disorders, including cancer, heart disease, and other degenerative diseases. This trend is the result of good marketing, not science.
Megadoses of vitamins have no beneficial effects
To date, scientific data have not established any beneficial effect of mega doses of vitamins on cancer, heart disease, and other degenerative disorders. Large clinical trials have found that taking multivitamins doesn’t lower the risk of disease compared with not taking a multivitamin. On the contrary, evidence indicates that far from reducing the risk of diseases, high doses of some antioxidant and vitamin supplements may increase it.
Possible adverse effects of high dose vitamin supplements
Vitamins have a wide margin of safety. Also, the body can excrete most of the extra multivitamins that we ingest. In healthy people therefore, doses that are just two to three times the recommended daily allowance (RDA), even if taken for a long period of time, will not lead to adverse effects. But regular intake of mega doses is another story.
Aside from the one you read, many reputable scientific studies indicate that regular intake of large-doses of vitamins has adverse effects. A few years ago, a highly publicized Swedish study that tracked some 35,000 women over 10 years found that those who took multivitamins were slightly more likely to be diagnosed with breast cancer than those who didn’t take the supplements. Studies on vitamin E show that those who take mega doses regularly are 13 percent more likely to develop—and 21 percent more likely to be hospitalized for—heart failure. While in men, mega doses of vitamin E increases the risk of prostate cancer. Vitamin E may likewise contribute to brittle bone disease or osteoporosis. Excessive intake of vitamin C, on the other hand, causes upset stomach and possibly kidney stone formation. The established toxic effects of vitamin A include loss of appetite, weight loss, enlargement of the liver and the spleen, anemia, peeling of the skin, fissures, and sores at the corners of the mouth, loss of hair, bone pain, and neuritis. Excess vitamin D increases blood calcium level, which can manifest as nausea and vomiting, loss of appetite, constipation, muscular weakness, confusion, tremor, lethargy and psychosis, irregularities of heart rhythm, and sudden death. Too much vitamin K results in destruction of red blood cells, which in infants leads to yellowing, enlarging of the liver, and even death.
Should you take vitamin supplements?
No need. You can get all the vitamins you need whatever your level of activity is from a balanced diet. Simply make sure that your diet contains a variety of fruit, vegetables, cereals, dairy, and protein.
Vitamin supplements are indicated only for pregnant and lactating women, the very young and the very old, and sick or convalescing people.
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