Vitamin supplements can be good for you — but only if taken in the right doses under the right conditions. In fact, taking vitamin supplements without professional guidance can be harmful.

In a recent report, Susan Whiting, a professor of nutrition at the University of Saskatchewan in Saskatoon, considered the benefits and drawbacks of taking vitamin supplements.

“We were happy to find that there are benefits to taking some vitamins, or even a multivitamin,” Whiting says. “However, people should be talking to a health professional if they do take vitamin supplements.”

Helene Charlebois, a registered dietician and nutritionist withHC Nutrition Consulting and Wellness in Ottawa, recommends an everyday multivitamin tablet for her patients. It is generally a safe bet, she says, because it contains small amounts of each of many nutrients in one pill and can supplement a balanced diet.

“My concern is with what I call ‘vitamin cocktailing’,” Charlebois adds, “in which people take large amounts of single vitamin supplements. That’s when the danger comes in.”

For example, if you take a calcium supplement and an iron supplement at the same time, the calcium may block your absorption of the iron.

Besides, says Rosie Schwartz, a registered dietician in Toronto and author of The Enlightened Eater’s Whole Foods Guide, a single supplement will provide one nutrient, whereas foods give you many other nutrients. Spinach, for example, is high in iron but it also has foliate, vitamin E and other nutrients.

“If you are going to replace spinach with a single vitamin supplement,” Schwartz says, “you may be missing out on the other nutrients.

“Supplements are to supplement a healthy diet,” she adds, “not to replace healthy foods.”

Here is a brief guide to some of the vitamins we need:

> Vitamin D. Canada’s food guide recommends 400 international units of vitamin D daily, which the body produces naturally through exposure to the sun. Because the Canadian climate gives us limited exposure to the sun, our bodies may produce less vitamin D than we need at certain times of the year.

It is also difficult to get vitamin D from your diet. But, Schwartz says, vitamin D is necessary at every stage in life, and deficiencies are being linked to an increase in autoimmune diseases such as Type 1 diabetes and multiple sclerosis and, as people age, colon cancer and prostate cancer.

“Many experts say 1,000 IU of vitamin D a day is better,” she says.

> Vitamin C. New research suggests vitamin C helps with the prevention of arthritis, says Charlebois. It also promotes iron absorption. Health Canada recommends 55 IU a day, about the amount in many multivitamins. But vitamin C is water-soluble; if you take more vitamin C than you need, up to 1,000 IU, excess amounts will come out in your urine. Much larger amounts, such as 10,000 IU, may cause diarrhea.

> Vitamin B. Breads and cereals are fortified with the B vitamins niacin, folic acid and riboflavin. Pregnant women need folic acid, found in supplements, because it has been shown to reduce the risk of birth defects such as cleft palate and spina bifida.

“White-flour products have been fortified with folic acid,” Schwartz says. “[As a result,] incidences of these types of birth defects have decreased.”

The downside of this is that the very property that enables B vitamins to help prevent birth defects — promoting cell regeneration — may also make them a cause of cancer in adults. “When you are an adult, you don’t want cell regeneration because you are grown,” Charlebois says. “Cancer is caused when a cell starts reproducing and has nowhere to go, so it starts dying. That’s the cancer tumor.”

> Vitamin E. In the 1960s and ’70s, scientists believed vitamin E was effective in warding off heart disease. But that might not be the case. While vitamin E is known to lower cholesterol, it lowers both LDL (“bad”) and HDL (“good”) cholesterol.

For people taking cholesterol-lowering medication, vitamin E in higher doses, such as 400 IU, could reduce HDL to dangerously low levels. Doses of vitamin E found in multivitamins, up to 200 IU, are considered safe, Schwartz says.

Cancer patients, especially those on chemotherapy, should be aware that some vitamins, in addition to B vitamins, can hasten the growth of cancer cells, according to Schwartz. They should speak to their oncologist or a dietician before taking vitamins.

@page_break@Is it better to get vitamins from foods than supplements? Ideally, it is, says Schwartz. But if you think supplements are necessary, consult a health professional. IE