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Patients come in to my office every day asking me about what vitamins to take. It is often confusing to sort out which vitamins do what, if they are helpful, or as recent evidence has suggested, if they can actually be harmful. Vitamins are organic compounds that the body needs in small quantities to function. These are micronutrients that, for the most part, our body does not produce. For example, vitamin D is a fat soluble vitamin that is found in food but it can also be made in our bodies after exposure to UV rays from the sun. Minerals, such as calcium, zinc and selenium, are solid and are also required by the body.

We know that vitamin deficiencies can lead to certain diseases, such as rickets in children who don't get enough vitamin D. But the question patients often ask is, can vitamins be used as primary prevention - a way to stop disease before it starts?

The answer is complicated. A recent study published in the Journal of the American Medical Association pooled together existing studies on antioxidants to answer this question about vitamins A, C and E, among others. Their results were distressing. The authors found that antioxidants such as beta carotene and vitamins A and E given alone or in combination actually increased the chance of dying. Vitamin C did not increase the chance of dying, but it did not show that it increased your chances of living longer, either.

However, it should be understood that this information does not come from one large study, but by looking at the conclusions of many smaller studies put together. In many of these studies, people taking the vitamins already had an existing disease. It is hard to know if healthy people taking antioxidants would also show that same increase in death that these authors associate with the use of antioxidants.

Another trial, know as the Heart Protection Study, looked at use of vitamin E in a group of people at high risk of developing heart disease and did not find any such increase in death. Among the high-risk individuals who were studied, the cocktail of antioxidant vitamins (650 milligrams of vitamin E, 250 mg vitamin C and 20 mg beta-carotene) appeared to be safe, but it did not produce any significant reductions in the five-year mortality from, or incidence of, any type of vascular disease, cancer or other major illness.

The news for vitamin B and folic acid was also not good in high-risk populations. Two studies, HOPE (Heart Outcomes Prevention Evaluation) and NORVIT (Norwegian Vitamin trial), looked at the use of vitamin B and folic acid in people who had diseases of the vascular system such as having had a heart attack. Both these studies did not find any benefit to the group using these vitamins.

Confusing to be sure. But there is a large body of evidence for the use of vitamins and minerals in many other instances. The Age-Related Eye Disease Study found that taking high levels of antioxidants and zinc can reduce the risk of developing advanced age-related macular degeneration by about 25 per cent, one of the most common causes of blindness.

The data for calcium are very clear. Calcium and vitamin D are both critical to develop and maintain bone health. Experts believe that our daily recommended intake of vitamin D is too low and that we should encourage intake of 1,000 IU in our adult population to prevent and treat osteoporosis, a bone-thinning disease. Calcium intake in adults should be between 1,200 and 1,600 mg. In addition, there is new evidence for vitamin K and its role in protecting against bone loss.

There has been some attention put toward the claim that calcium can promote weight loss. While a calcium-rich diet might result in a greater loss of body fat, there really is no convincing evidence that a calcium supplement will do the same.

The role of calcium in colorectal cancer has also been studied. In the Calcium Polyp Prevention Study, subjects were given 1,200 mg of elemental calcium for four years. A greater effect of calcium on risk reduction for colorectal cancer polyp recurrence was seen in those with high-blood levels of vitamin D. Among women taking multivitamins with folic acid for 15 or more years, the risk of colon cancer was 75 per cent lower as reported in the Annals of Internal Medicine.

There is also strong evidence showing that pregnant women need 400 micrograms of folic acid a day to reduced the risks of giving birth to a child with a neural tube defect such as spina bifida. Furthermore, pregnant women require extra iron.

Chromium is a mineral that has been studied in its relationship to diabetes. It might be a key nutrient in decreasing insulin resistance in patients with Type 2 diabetes.

Another mineral that has shown promise is selenium. In the study reported in the Journal of the American Medical Association, its use did, in fact, show a reduction in mortality. In The Nutritional Prevention of Cancer Trial reported by the U.S. National Cancer Institute, those with the highest selenium intakes were associated with the lowest risk of prostate cancer.

Lycopene, a powerful antioxidant derived from plants, can also be found in nutritional supplements. Its dietary source includes tomatoes, watermelon and apricot among other fruits.

Recent studies have begun to examine its possible role in preventing cancer, and in particular prostate cancer.

Ongoing studies are looking at its potential role in the prevention of coronary heart disease, osteoporosis, hypertension and pre-eclampsia in pregnancy.

So where does all this leave us? As we watch the information evolving, it means that right now we do not have all the answers.

As always, your first defence for health is a diet rich in your required micronutrients. Exercise, don't smoke, and watch your weight. Sit down with your physician and review what supplements are best for you.

Dr. Marla Shapiro can be seen Tuesdays on CTV's Canada AM.