For so long, it seemed so easy. Vitamins were good for you, so why not pop a daily pill, an easy-to-swallow insurance policy against colds or more serious diseases such as cancer or heart disease?

But a growing number of experts are warning that generally healthy people may be overdoing it on vitamin supplements -- particularly vitamins A, E and C -- especially in combination with a healthy diet that contains fortified foods such as milk or cereals. There is no proof that taking vitamin pills offers protection against any disease, but there is some evidence that in some cases, supplements may actually increase the risk of getting cancer or osteoporosis.

"I don't think you should arbitrarily take a supplement. If you are eating a healthy well-balanced diet and consuming food from all four food groups, you need to question whether you need to take a multi-vitamin," says Theresa Glanville, an associate professor in the department of applied human nutrition at Mount Saint Vincent University in Nova Scotia. She doesn't take vitamins.

It has been well established for years that a deficiency in a particular vitamin can cause illness. A lack of Vitamin D, for example, can cause rickets, a softening and weakening of the bones. Too little Vitamin C leads to scurvy.

It has also been known for years that large amounts of some vitamins can be toxic.

Vitamin consumption began rising during the 1950s and '60s, which brought exciting findings that indicated some vitamins might actually protect against cancer and other diseases.

Vitamins C and E and beta-carotene are antioxidants that help the body deal with free radicals. Free radicals occur when our bodies use oxygen, and they damage cells the same way rust damages a car. Antioxidants stop free radicals from forming and bind with those already in the body to prevent the cellular "rusting" that can lead to cancer and other illnesses.

Many doctors and nutritionists began recommending that people take vitamin supplements, reasoning that moderate amounts of vitamins don't do any harm and may be good preventive medicine. But proof of that proved elusive. Study after study has failed to find that vitamin supplements reduce the risk of disease.

What the research has found, however, is that vitamin A, E and C supplements could increase the risk of some health problems.

Last week, a U.S. team of researchers found that taking 25 milligrams a day of beta-carotene, a precursor to vitamin A, increases the risk of colon cancer in people who smoke and consume at least one alcoholic drink a day. Many multi-vitamin pills in Canada contain at least this much beta-carotene.

Studies have suggested that too much vitamin A can reduce bone density, which increases the risk of osteoporosis. In high levels, it can also cause birth defects.

There is some evidence that taking vitamin E can increase the risk of stroke in women, and that too much vitamin C can cause digestive problems, including nausea, abdominal pain, flatulence and diarrhea.

How much is too much? It depends on the vitamins you take, and your diet.

Since the early 1990s, Canadian and U.S. dietary experts have worked together, through the National Academy of Sciences in the United States, to evaluate the existing research on vitamins and minerals. They determined a healthy range of vitamin consumption, but they also took a new approach and set a safe upper limit -- defining for the first time how much may be too much.

The upper-limit guidelines are part of a new way of looking at vitamins that Health Canada is planning to adopt.

In the United States, a growing number of doctors and medical researchers are worrying that people are taking more vitamins than is good for them, according to a recent article in The New York Times.

Canadian researchers share the concerns about overuse, but say the situation in Canada may not be exactly the same. Americans may be ingesting more vitamins than Canadians, says Dr. Katherine Gray-Donald, director of the school of dietetics and human health at McGill University in Montreal. That is because more of their food is fortified with vitamins and other nutrients -- and in some cases to a greater degree -- than in Canada.

"I brought home a box of cereal from the U.S. and it had the daily recommended intake of calcium in one bowl," she said. "When my husband took a second bowl, I told him, "You can't have two bowls of that cereal." (Too much calcium may lead to kidney stones.)

Health Canada has a more conservative approach to fortifying foods than the United States, and some critics have called it overly restrictive. Canadian milk is fortified with Vitamin D. Salt is fortified with iodine. In cases where nutrients are removed from food during processing -- for example, some of the vitamins, iron and folic acid that occur naturally in flour -- manufacturers are allowed to put them back. Vitamin A can be added to margarine so it can compete nutritionally with butter.

But food manufacturers are not permitted to add vitamins to any product they see fit.

That approach is now under review. Health Minister Anne McLellan announced last week that Canada will give food manufacturers more discretion in terms of which products can include extra vitamins. Exactly how the new system will work is still unclear. Consultations will take place in Ottawa at the end of the month. No decisions will be made on approving new products until the fall.

There is a heated debate among experts over whether inexpensive but popular foods such as chips or pop should be fortified with vitamins. This would improve the diets of low-income Canadians who can't afford the fruits and vegetables needed for a healthy diet, says Harvey Anderson, a professor of nutritional science at the University of Toronto.

Canadians who eat a healthy diet and take vitamins tend to be well educated and have higher incomes, he says. He is worried the government will not allow companies to add vitamins to more food products for fear that higher-income Canadians will end up with an overloaded diet, according to the new safe upper limits for vitamins.

He also says the science on which those new limits are based is questionable.

"You are ignoring the people who are at risk of having inadequate intake. In a sense, it is protecting the rich and foolish at the expense of the poor. To me, public health means you look at both ends of the spectrum," Dr. Anderson says.

Karen Dodds, director-general of Health Canada's food directorate, says research is under way to see if there is a nutrition gap in Canada, but the current evidence suggests there isn't one, at least as far as vitamins and minerals are concerned. "We don't see population deficiencies in vitamins and minerals."

She also says she hasn't seen any evidence that shows Canadians are overdoing it on vitamins and minerals.

There is some evidence, however. Dr. Gray-Donald recently published a study that found Canadians were taking in too much niacin, a B vitamin many people take to lower the risk of heart disease. The safe daily upper limit is 35 mg, and some multi-vitamins have 50.

Taking too much doesn't cause serious health problems, but it can cause flushing, which can send people to their doctor worried they are suffering from something more serious.

Her survey of Canadians didn't find more serious vitamin overdoses, although it asked only about vitamin pills or supplements that people had taken in the past 24 hours. A survey that asked about weekly habits might have produced different results, she says.

No one is saying Canadians should stop taking vitamins, which offer a variety of health benefits. Folic acid, taken before a woman gets pregnant and in the first few months after conception, has been proved to reduce birth defects such as spina bifida.

There are also tantalizing signs -- circumstantial evidence -- of the good they may do in preventing disease.

"We still need proof, but there are many signs that B vitamins are good for the heart," says David Spence at the Robarts Research Institute in London, Ont. He believes in taking supplements, at least of the B vitamins.

Researchers have found that vitamins B-6 and B-12 can reduce levels of a naturally occurring chemical called homocysteine, which damages the lining of the arteries. People with high levels of homocysteine are at greater risk for heart attack and stroke.

But two large studies found no evidence that B-6 and B-12 reduce the incidence of heart attack and stroke.

Dr. Spence believes that proof the B vitamins help to prevent heart disease will soon materialize, and in the meantime, he takes them regularly.

Other experts, like Dr. Glanville, say that, in general, it's better to get your vitamins through a balanced diet. Plenty of studies show that a diet rich in veggies and fruit reduces the risk of getting cancer or heart disease. This probably means that more than just the vitamins in food help prevent disease.

"A tomato on the vine produces all kind of chemicals that protect it in a harsh environment. When we eat it, some of that protective effect is being transferred to us."

Anne McIlroy is The Globe and Mail's science reporter.

Vitamin ABCs:

VITAMIN A

How much do adults need?

900 micrograms a day for men and 700 for women

How much may be too much?

3,000 micrograms a day for both men and women

Food sources

Orange fruits and vegetables such as squash, pumpkin, carrots, sweet potatoes and mango; vegetables with dark green leaves such as spinach and broccoli; liver

Amounts found in typical servings

Three spears of raw broccoli: 462 micrograms; one green pepper: 189 micrograms

What it does

It's important for a healthy immune system and for good vision

VITAMIN C

How much do adults need?

90 milligrams a day for men, 75 milligrams a day for women

How much may be too much?

2,000 milligrams a day

Foods sources

Citrus fruits such as orange and grapefruit, strawberries, tomatoes, papaya; red and green peppers and spinach

Amounts found in typical servings

One orange: 53 mg; one red pepper: 190 mg

What it does

It is an antioxidant that protects against the damage caused by free radicals

VITAMIN E

How much do adults need?

15 milligrams a day

How much is too much?

1,000 mg a day

Food sources

Almonds, walnuts, wheat germ, avocado, whole grains, corn oil, sunflower seeds

Amounts found in typical servings

One ounce of almonds: 7.5 mg; two tablespoons of peanut butter: 3.2 mg

What it does

It is an antioxidant

Who takes vitamins?

Income, education and gender are key factors.

Sixty-six per cent of Canadians with university degrees take vitamins, compared to 53 per cent with a high school diploma or lower.

In homes with a household income of $70,000 or more, 64 per cent take vitamins. When income is less than $35,000, the figure drops to 56 per cent.

Percentage of men

who take vitamins:

50

Percentage of women:

67

Sources: The Recommended Intakes for Individuals and the Tolerable Upper Intake Levels, The National Academy of Sciences (recommended intakes vary for children, for pregnant and lactating women, and for the elderly).

Gerry Harrington, the Nonprescription Drug Manufacturers Association of Canada.