Do dietary supplements really work?

It's not good news for users of echinacea, black cohosh, and freeze-dried tissue from the New Zealand green-lipped mussel.

Millions may be buying them to combat the ills of conditions as diverse as the common cold, hot flushes, and arthritis, but the latest evidence raises questions about just how effective they are.

Echinacea, one of Britain's top-selling supplements on which, according to some estimates, we spend £1m or so a month trying to prevent the common cold or ease its passage, is the latest to be found wanting.

"The latest study on echinacea, one of the best ever conducted, found it was not effective for prevention of the common cold or for treating the symptoms. In other words, it doesn't work,'' says Professor Edzard Ernst, director of complementary medicine at Exeter University whose study on the green-lipped mussel supplement has found little consistent evidence for its use as a rheumatoid or osteoarthritis treatment

In America, another major study has found that black cohosh, another of the big hitters, is no better than a placebo for menopausal hot flushes. " Regrettably, we found that it has little potential to play an important role,'' says lead researcher Dr Katherine Newton.

Health supplements such as echinacea and black cohosh are big business. It's estimated that we now spend more than £300m a year on supplements of one kind or another in the UK, and that demand is increasing, with one in five people using them at some time, and almost half of British women in their fifties regularly popping one or more. Those suffering from serious and chronic illnesses, including cancer, diabetes, arthritis, and Alzheimer's are also increasingly turning to supplements.

But while there is evidence that some work, the data for most is conflicting or doubtful. There is also concern about safety. While supplements are bought in the belief that they act on the body or mind, there is little or no control over what is in them, or what it does.

Research at Consumer Lab, an American organisation devoted to testing off-the-shelf supplements, demonstrated that quality varies widely. Out of some 14 ginseng supplements, six did not contain the amounts claimed and three exceeded permitted pesticide levels.

"Research in America shows that off-the-shelf preparations contain anything between zero and 200 per cent of what it says on the label," says Professor Ernst. "The same thing is happening here, and I would like to see much greater regulation.

"European regulations are coming in which will give greater protection for consumers, but they don't require demonstration of efficacy, either, says Professor Ernst.

The EU directive on traditional and herbal medicines, which regulates the safety and quality of products, came into force this week. It gives manufacturers seven years to comply with new regulations.

Big differences in quality and actual, rather than stated, quantity of products may be one reason for the often conflicting research results. Small sample size and lack of proper controls is another problem.

Another challenge for those investigating whether supplements work is that evidence can be influenced by other factors, such as the type of people who participate.

Researchers at the Medical Research Council in Cambridge looked at the long-term use of supplements by almost 2,000 people born in 1946. They found that those who used supplements tended to be non-smokers who took exercise, weighed less and had slimmer waists and higher blood levels of vitamin B12.

Non-supplement users tended not to eat healthy foods, such as breakfast cereals, fruit, fruit juice, yoghurt, oily fish, and olive oil. They had low levels of potassium, magnesium, phosphorus, iron, and vitamin C in their diet.

Ironically, it tends to be those who need supplements the least that use them the most: "Dietary supplement users tended to have diets that were healthier. Those taking supplements may be the least likely to need them."

GARLIC

A total of 37 trials consistently showed that compared with placebo, various garlic preparations lead to small but statistically significant reductions in total blood cholesterol after one month. Another 27 small trials reported mixed but never large effects for garlic on high blood pressure.

One trial, with 492 people, found no statistically significant drop in numbers of heart attacks when participants were taking six to 10 grams of garlic compared with placebo. Scant data suggest, but do not prove, that dietary garlic consumption is associated with decreased odds of suffering from laryngeal, gastric, colorectal, and endometrial cancer.

Studies suggest, but do not prove, that dietary garlic is not associated with [reductions in] breast or prostate cancer,'' says the US Agency for Healthcare Research and Quality.

BLACK COHOSH

This is extensively used by women for menopausal symptoms, and increasing numbers have been turning to supplements following concern about the side-effects of HRT. A much-anticipated American study, Herbal Alternatives for Menopause, has found that that black cohosh offers little relief; no significant differences were discovered in the frequency or intensity of hot flushes in women who were using herbal supplements and those using the placebo.

ECHINACEA

Is traditionally used to treat or prevent colds, flu, and other infections. The theory is that it stimulates the immune system to help fight infections. But two big studies in America did not find a benefit from echinacea, either as the fresh-pressed juice of Echinacea purpurea for treating colds in children, or as an unrefined mixture of Echinacea angustifolia root and Echinacea purpurea root and herb in adults.

FISH OIL

Contains high amounts of two omega-3 fatty acids, and there is evidence that the body uses these to counteract inflammation. Widely used by arthritis sufferers. "There is some evidence about the potential usefulness of fish oil or omega-3 supplementation for aspects of rheumatoid arthritis, including tender joints and morning stiffness,'' says the US Agency for Healthcare Research and Quality. Research also shows that a diet rich in omega-3 may lower risk of heart disease, diabetes and depression, age-related cognitive decline, high blood pressure in babies, and neurological disorders. It may also lower bad cholesterol.

GINKO

Leaf extracts are used to improve memory, treat or help to prevent Alzheimer's and other types of dementia, to reduce leg pain caused by narrowing arteries, and to treat sexual problems, multiple sclerosis and tinnitus. "The evidence is that it is very effective for two conditions, dementia symptoms and peripheral artery disease,'' says Professor Ernst.

GLUCOSAMINE

Glucosamine and chondroitin are both naturally occurring substances that are found in and around the cells of cartilage. Researchers say that the evidence for glucosamine's effectiveness is clearly positive: "It helps to restore function and even restore cartilage in osteoarthritis."

MULTIVITAMINS

The American Preventive Services Task Force found that there is insufficient evidence to recommend for or against the use of supplements of vitamins. Most health advice is that a good diet should ensure adequate vitamin levels for most people.

"There is inadequate evidence that vitamins, whentaken to supplement a healthy diet, can prevent heart disease or cancer," says the US Agency for Healthcare Research and Quality.

SELENIUM

One large study showed that taking a daily supplement of the mineral selenium significantly reduced the risk of death from prostate cancer, colon cancer and lung cancer. It's thought that selenium may prevent or slow down the growth of tumours. But a second big study found that women who had higher levels of selenium did not have a reduced risk of cancer. Research also shows that people suffering from rheumatoid arthritis have reduced selenium levels in their blood.

ST JOHN'S WORT

Widely used for mild to moderate depression. There is increasing evidence that it has an effect, although there are concerns about interactions with other treatments. A review of 23 clinical studies found that the herb might be useful in cases of mild to moderate depression. The studies, which included 1,757 outpatients, showed that it was more effective than a placebo. Another study found that it was not effective for treating major depression.

ZINC

Zinc is an essential mineral that is found in almost every cell in the body. The effect of zinc treatments on the severity or duration of symptoms of the common cold is disputed. A study involving more than 100 employees at the Cleveland Clinic in the United States indicated that taking zinc lozenges reduced the length of colds by half, although no differences were seen in how long fevers lasted, or in the level of muscle aches experienced by sufferers. But a second study found no differences between those having zinc and those who were receiving a placebo.