More than £100m a year is spent on them and 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 capsules and tablets used to try and 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 5 per cent. When they looked at individual vitamins, E increased mortality by 4 per cent, betacarotene by 7 per cent, and A by 16 per cent. No effect was found for vitamin C or selenium.

The Danish researchers are not the first to find negative effects from taking vitamin pills: “Evidence is insufficient to prove the presence or absence of benefits from use of multi-vitamin and mineral supplements to prevent cancer and chronic disease,” say researchers from Johns Hopkins University in Baltimore, Maryland. A study by a team at the same university 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 you feel you can’t do that, which vitamins and minerals are worth taking?

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 they play a part in control and repair of tissues. There are two types: fat-soluble and water-soluble. Fat-soluble - 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 C and folic acid, are 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 that the 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 per cent increase in mortality.

Bottom line “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

A carotenoid, it is a vitamin A precursor, which the body converts into vitamin A. 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 7 per cent increased risk of mortality associated with taking the pill. Other studies have shown a link between betacarotene and increased risk of lung cancer in smokers. In one trial, 18 per cent more lung cancers were diagnosed and 8 per cent more deaths occurred in those taking betacarotene. In a second study, 28 per cent more lung cancers were diagnosed and 17 per cent more deaths occurred in those taking betacarotene and vitamin A supplements than in those taking placebos. Neither of these studies showed a benefit from taking supplements.

Bottom line “Given the mixed evidence, it may be wise to avoid taking betacarotene supplements, and instead obtain this nutrient through food and a multi-vitamin,’’ 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.

Bottom line “Taking a multi-vitamin that contains 400 micrograms of folic acid is good insurance,’’ says the Harvard report.

VITAMIN C

An antioxidant, it boosts the immune system, fights infection, helps wounds heal and maintains health of gums, teeth, bones and blood vessels. It is found naturally in most fruits and vegetables.

Some research suggests that while it does not cure the common cold, vitamin C in the diet may ease the symptoms. There is also evidence that long-term use of supplemental vitamin C may protect against cataracts. A study in Dubai suggests vitamin C supplementation in infertile men may improve sperm count.

Bottom line Experts currently recommend not taking large doses of vitamin C to guard against heart disease: “It’s much better to get what you need from food. 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 after three years, those patients aged over 65 taking supplements had better bone health than other over-65s. Study of US military shows vitamin D may help prevent multiple sclerosis.

Bottom line “Vitamin D inhibits the growth of cancer cells in test tubes, and is starting to show some promise in cancer prevention and treatment. Aim for 800 micrograms per day from a multi-vitamin, in addition to whatever you are able to get from the sun,’’ says the Harvard report.

VITAMIN E

Antioxidant that protects the body from damage caused by free radicals, which harm cells, tissues and organs, and are believed to be one of the causes of the degenerative diseases that come with age. Natural sources include whole grains, green leafy vegetables, nuts, fish and meat.

Supplements have been used to try and boost brain power, and reduce the risk of cancer and heart disease, but trial results are mixed.The Copenhagen study found a 4 per cent increased risk of mortality associated with the vitamin.

Bottom line “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 of vitamin E to protect against heart disease. Try to eat a healthy diet and take a multi-vitamin,’’ says the Harvard report.

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, from hyperactivity to diabetes, according to a review of research by doctors at the University of Alberta.

Other research shows that children of mothers who consumed cod-liver oil daily after the 18th week of the pregnancy and during early breast-feeding had improved intelligence at the age of four. Current advice from the Food Standards Agency is that pregnant and breast-feeding women can eat between one and two 140g portions of oily fish a week.

Other studies have shown that men and women who eat fish at least once a week are half as likely to die from a heart attack. Another study showed that sudden-death rates among men who had suffered one heart attack dropped by 45 per cent with fish oil. A 14-year study showed that women who ate fish at least twice a week were half as likely to suffer strokes

Bottom line “We recommended that untainted fish oil containing abundant omega-3 fatty acids be considered as a routine supplement during pregnancy and lactation,’’ say the Alberta researchers.

MAGNESIUM

Helps build bones and teeth and plays a role in regulating blood pressure.

Bottom line “Make sure you meet the recommended amounts of magnesium by consuming magnesium-rich foods such as whole grains, leafy green vegetables, avocado and fish, and taking a multi-vitamin daily,’’ says the Harvard report.

POTASSIUM

Helps maintain steady heartbeat and may lower blood pressure.

Bottom line “While no compelling evidence favours potassium supplements, it’s worth your while to put potassium-rich foods, such as beets, bananas, oranges and broccoli on the menu.’‘

SELENIUM

Acts as an antioxidant, protecting cells.

Bottom line Although trial data indicates that selenium may reduce prostate, lung and colon cancers, doubts remain. Taking a supplement containing 200 micrograms of selenium a day may be good for men at high risk of prostate cancer, although some experts do not think there is enough evidence to support this approach.

ZINC

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

Bottom line “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.’‘

For more information: Vitamins and Minerals, What You Need to Know, Harvard Health Publications; British Nutrition Foundation (http://www.nutrition.org.uk); Food Standards Agency (http://www.food.gov.uk)

Supplements: the facts

• Take supplements with water at room temperature, as hot or chilled drinks can damage them.
• Don’t drink tea or coffee 15 minutes before or after taking supplements, because they interfere with nutrient absorption.
• Don’t take lots of different supplements because they can interact with each other and be less effective - zinc, for example, interferes with how copper and iron are absorbed.
• The UK health supplements industry is worth ?360m a year, of which vitamin and mineral supplements account for ?130m.
• Londoners spending ?8.22 per person per month on vitamins and minerals, compared to a low in the South West of ?1.88.
• We spend ?6.34bn a year on fresh fruit and vegetables.
• Americans spend ?300m a year on vitamin C supplements alone.