MILLIONS of people take them daily in the belief they boost health - but could vitamin pills really be unhealthy? According to a new report, some of those little pills used to try to ward off diseases as diverse as cancer, Alzheimer's, acne, arthritis and the common cold may be bad for you. "Treatment with betacarotene, vitamin A, and vitamin E may increase mortality, " say researchers from Copenhagen University Hospital.

While some research has shown beneficial effects for vitamins, minerals and other supplements, others have either found none, or produced conflicting results, or, in some cases, shown potentially harmful effects. The Danish researchers combined the results of a number of previous clinical trials to judge the overall effects of vitamin pills. The results show that, in 47 trials involving 180,938 people, antioxidant supplements increased mortality by five percent.

When they looked at individual vitamins, vitamin E increased mortality by four percent, betacarotene by seven percent, and vitamin A by 16%. No effect was found for vitamin C or selenium.

The researchers in Copenhagen are not the first to find negative effects from taking vitamin pills. Researchers from Johns Hopkins University in Baltimore, Maryland found that taking high doses of vitamin E may increase the mortality rate. "We think that high-dosage vitamin E supplementation may increase all-cause mortality. Current evidence does not justify using it to reduce the risk for cancer, cardiovascular or Alzheimer's disease, " the researchers say.

Vitamin A can also harm bones and high levels have been linked to birth defects, blood clotting and over-stimulation of the immune system, according to a new report from Harvard University. "A vast amount of research has shown that you can cut your risk for chronic disease and disability by following a healthy diet, as well as exercising regularly and avoiding smoking. The evidence for taking vitamin and mineral supplements is much less extensive, " says the report.

While the evidence for some supplements, including folic acid, is good, the advice for most people is to get as many vitamins as possible from a healthy diet.

But if that's not possible, which pills should we pop and which should we stop?

WHAT ARE VITAMINS AND MINERALS?

Vitamins are vital nutrients the body needs to work properly. They provide energy, boost the immune system, keep skin healthy, help keep the brain and nervous system in good working order and play a part in control and repair of tissues. There are two types: fat-soluble and water-soluble. Fat-soluble - vitamins A, D, E and K - are mainly found in fatty foods such as dairy products, liver and oily fish and are stored by the body when they are not needed. The others, including vitamin C and folic acid, are found in fruit and vegetables and are not stored in the body, which means they need to be eaten more often.

Minerals are essential nutrients found in varying amounts in a variety of foods, including meat, cereals, fish, dairy foods, vegetables, fruit and nuts.

VITAMIN A Boosts the immune system and is important for healthy bones, teeth, skin and eyesight. Found naturally in green leafy vegetables and in orange-coloured fruit and vegetables, as well as liver, eggs and fish oils. A study in the New England Journal of Medicine found men with the highest amounts of vitamin A in their blood had the greatest risk of breaking a bone. The Copenhagen report associates vitamin A with a 16% increase in mortality.

Stop or pop? "Plenty of evidence from earlier research shows too much vitamin A can harm bones. A pregnant woman who takes too much vitamin A risks birth defects to the foetus. Excess vitamin A also compromises bone health and blood clotting and it can over-stimulate your immune system, " says the Harvard report. Try to get this vitamin from food sources.

BETACAROTENE This carotenoid is a vitamin A precursor, which the body converts into vitamin A.

It is found naturally in a wide range of fruits and vegetables that are deep yellow, orange or dark green, such as carrots and spinach. The Copenhagen study found a seven-percent increased risk of mortality associated with taking the pill.

Other studies have shown a link between betacarotene supplements and increased risk of lung cancer in smokers.

Stop or pop? "Given the mixed evidence, it may be wise to avoid taking betacarotene supplements and instead obtain this nutrient through food and a multivitamin, " the Harvard study says.

VITAMIN B A group of water-soluble vitamins, including folic acid, involved in many of the chemical reactions in the body. Folic acid is found naturally in spinach, broccoli, mushrooms, dried beans, peas and whole grains, as well as liver and oranges.

Many studies have shown that folic acid helps protect against brain and spinal birth defects when taken early in pregnancy. A study at Wageningen University in Holland shows that taking folic acid supplements slowed the decline in hearing in older people.

Stop or pop? "Taking a multi-vitamin that contains 400 micrograms of folic acid is good insurance, " says the Harvard report.

VITAMIN C Vitamin C is an antioxidant that boosts the immune system, fights infection, helps to heal wounds and maintains the health of gums, teeth, bones and blood vessels. It is found in most fruits and vegetables. Some research suggests that vitamin C may ease the symptoms of the common cold. There is also evidence that longterm use of supplemental vitamin C may protect against cataracts. A study in Dubai suggests vitamin C supplementation may improve sperm count.

Stop or pop? Experts recommend not taking large doses of vitamin C to guard against heart disease: "There is no need to take more vitamin C than is available in a standard multi-vitamin, " says the Harvard report.

VITAMIN D Promotes the body's absorption of calcium, essential for maintenance of healthy bones and teeth, as well as nerve cells. Sunlight is the main source, but vitamin D is also found in oily fish, milk, liver and eggs. Studies at the Cancer Research Center of Hawaii show that vitamin D may lower the risk of colon cancer. One study in the New England Journal of Medicine shows that those patients over 65 taking supplements had better bone health than other over-65s. Study of US military shows vitamin D may help prevent multiple sclerosis.

Stop or pop? "Vitamin D inhibits the growth of cancer cells in test tubes and is showing promise in cancer prevention and treatment." The Harvard report reecommends daily intake of 20 micrograms from a multi-vitamin, in addition to whatever you get from the sun.

VITAMIN E Antioxidant that protects the body from damage caused by free radicals. Free radicals harm cells, tissues and organs.

Natural sources include whole grains, green leafy vegetables, nuts, fish and meat. Supplements have been used to try to boost brain power and reduce the risk of cancer and heart disease but trial results are mixed. The Copenhagen study found a four-percent increased risk of mortality associated with the vitamin.

Stop or pop? "The evidence is not strong enough to recommend taking extra vitamin E to lower the risk of most cancers.

The experts do not recommend taking large doses to protect against heart disease, " says the Harvard report.

FISH OIL Fish oil has been linked to lower levels of heart disease and cancer, as well as chronic diseases. Fish oil during pregnancy may lower high blood pressure, prevent an early birth and reduce the risk of a wide range of health problems. Current advice from the Food Standards Agency is that pregnant and breastfeeding women can eat between one and two 140g portions of oily fish a week.

Some studies have shown that eating fish at least once a week may reduce deaths from heart attack. A 14-year study showed that women who ate fish at least twice a week were half as likely to suffer strokes Stop or pop? Untainted fish oil containing abundant omega-3 fatty acids should be considered as a routine supplement during pregnancy and lactation.

MAGNESIUM Helps build bones and teeth and plays a role in regulating blood pressure. Found in whole grains, leafy green vegetables, avocado and fish.

Stop or pop? The Harvard report recommends meeting the recommended amounts of magnesium from diet and by taking a multi-vitamin daily.

POTASSIUM Helps maintain steady heartbeat and may lower blood pressure.

Stop or pop? It's worth eating potassium-rich foods, such as beets, bananas, oranges and broccoli.

SELENIUM Acts as an antioxidant, protecting cells.

Stop or pop? Although trial data indicates selenium may reduce prostate, lung and colon cancers, doubts remain. Taking 200 micrograms of selenium a day may be good for men at high risk of prostate cancer.

ZINC Involved in the growth of new cells. Some research suggests a beneficial effect in the treatment of age-related macular degeneration (AMD).

Stop or pop? "If you have already been diagnosed with AMD, talk to your doctor about whether you should consider taking a combination of zinc and antioxidant vitamins."