When it comes to vitamins, think about the alphabet. Vitamins A, B, C, D and E are incredibly popular, and consumers spend hundreds of millions of dollars a year on products that contain them. True vitamin deficiencies, except for Vitamin D, are rare. We usually take them in an effort to prevent problems and to stay healthy, yet there is a surprising lack of evidence that they help.

Vitamin D is now the hot vitamin, and it seems as if everyone is taking it. A large number of people may be deficient; in one study, 60 percent of nursing home residents were deficient in vitamin D. Treating this can reduce the risk of hip fracture in the elderly, and can improve bone mineral density. But other evidence suggests that supplementing does not really help. A new study just published in JAMA Cardiology, by researchers in New Zealand, has shown that monthly intake of high-dose Vitamin D did not prevent cardiovascular disease. When compared with a placebo, vitamin D serum levels went up much more in the group taking D, but the chance of developing coronary disease was the same over three years, just under 12 percent for both groups. The doses were large: 100,000 international units a month. Since recommended doses are currently 600-800 IU a day, is was disappointing to find out that the effect was zero.

Vitamin D has also been studied for cancer prevention. A recent trial, published in JAMA, looked at Vitamin D3 2,000 IU a day compared with a placebo, and showed no effects on cancer rates.

Vitamin B was the hot vitamin a few years ago, but supplementing with it has fallen out of favor. Taking it lowers the level of  a blood amino acid called homocysteine, which irritates blood vessels. High levels of homocysteine are bad for cardiac health, but despite this, evidence has shown that lowering homocysteine levels does not change the course of disease. Unless you have a deficiency, or are pregnant, taking any of the B vitamins probably will not help as much as we used to think.

Vitamin C supplementation is even more controversial. It has been used for years to prevent the common cold, but does it? Although some studies have suggested that taking it may reduce the duration of a cold, the effect is probably minimal.

So, where does this leave us when it comes to supplementing with vitamins?  If you are confused, it is with good reason. The truth is that we do not know right now. The scientific data are not clear, as studies seem to come out weekly on both sides of the issue. Here are some take-home messages on the alphabet vitamins:

  1. If you follow a good diet, rich in fruits and vegetables, it is unlikely that you need any vitamin supplements at all.
  2. Smoking interferes with the absorption of Vitamins C and D. Stopping smoking is a vastly smarter approach than taking more pills, but if you smoke, it is best to supplement with these vitamins.
  3. People who have nutritional problems often need extra vitamins and minerals. If you eat less than 1,200 calories a day, have a condition that leads to malabsorption of foods and vitamins from your intestine, have had bariatric surgery, are a strict vegetarian, or you are pregnant, you likely should be taking vitamins.
  4. Vitamin D and calcium can help prevent osteoporosis, and you should speak to your doctor about the pros and cons of taking these supplements. Vitamin D, usually in doses of 1,000-2,000 IU a day, has been shown to possibly help with fatigue, and muscle aching, including the kind that has been associated with statins. Vitamin D supplements containing cholecalciferol (D3) seem to be more potent than another form of vitamin D (D2) called ergocalciferol.
  5. Labels can be misleading. Remember that supplements are not regulated by the FDA, and outrageous claims can be made without evidence.
  6. All the alphabet vitamins can be toxic at high doses.
  7. Not all vitamins are the same. Fat-soluble vitamins such as A, D, E and K are stored longer in your body, and stay around longer than water-soluble vitamins, which are excreted by sweat and urine.
  8. Multivitamins are advertised all the time, but do you really need one? No one knows for sure. A recent analysis looked at the use of multivitamins in older men, and found no benefit.
  9. If you are going to buy a vitamin, more expensive is not always better. Supplement makers want your money, and sometimes we think more expensive means better quality. This may not be true in all cases. One way to find good-quality vitamins is to look for independent certification.  Three organizations that evaluate over-the-counter supplements for purity include  USP (United States Pharmacopeia), NSF International, and ConsumerLab.  Look for a label on the bottle from one of these organizations or check their websites.
  10. A large portion of the vitamins that you take will be excreted. Although most are safe and will do no harm, there are no health benefits to be gained by having expensive urine.

David Becker, M.D., is a runner and a board-certified cardiologist with Chestnut Hill Temple Cardiology in Flourtown, Pa. He has been in practice for 25 years.