Tuesday, December 23, 2008

Vitamins key to health? Not necessarily so

Dec 23, 2008

Large doses of such supplements may even be harmful: Studies

LOS ANGELES: - Vitamin pills - wonder pills thought to play a crucial role in preventing some of the most intractable illnesses - have lost their lustre.

Results of clinical trials, designed by The National Institutes of Health to quantify the disease-fighting abilities of vitamins and minerals, have not shown benefits from taking them.

This month, two long-term trials involving more than 50,000 participants offered fresh evidence that vitamin C, vitamin E and selenium supplements do not reduce the risk of prostate, colorectal, lung, bladder or pancreatic cancer.

Research has even suggested that, in some circumstances, vitamin and mineral supplements can be unsafe.

Some physicians now advise patients to rely instead on a healthy diet for needed vitamins and minerals.

'These things are ineffective, and in high doses they can cause harm,' said Dr Edgar Miller, a professor of medicine and epidemiology at Johns Hopkins University School of Medicine in Baltimore.

Yet, faith in vitamins runs deep. The Council for Responsible Nutrition, a Washington DC-based trade group, estimated that 64 per cent of Americans take vitamin and mineral supplements.

Despite the steady drumbeat of reports questioning their efficacy, sales have risen consistently from US$5 billion in 1995 to US$10 billion (S$15 billion) this year, according to the Nutrition Business Journal.

Scientists remain convinced that vitamins are essential to health. But they are puzzled over how their obvious benefits could be so elusive in randomised controlled trials, the gold standard of medical research.

Unlike observational studies, which look backward at groups of people to identify factors that are associated with a particular disease, a forward-looking randomised controlled trial has the power to show that a particular factor can prevent the disease.

'You really do need vitamin E. You really do need vitamin C. You really do need selenium,' said Dr Jeffrey Blumberg, director of the US Department of Agriculture's Antioxidants Research Laboratory at Tufts University in Boston. 'Without them, you die.'

Researchers have identified several reasons why vitamins do not lend themselves to random controlled trials. Chief among them is that there is no true placebo group when it comes to vitamins and minerals because everyone gets some in their diet.

'For drugs, someone either has (the impotence drug) Cialis in their system or he doesn't,' said Dr Paul Coates, director of the National Institutes of Health Office of Dietary Supplements in Maryland. With vitamins, 'there's a baseline exposure that needs to be taken into account. It makes the challenge of seeing an improvement more difficult'.

Meanwhile, researchers will return to traditional observational studies to learn more about the role of nutrition in fighting disease. 'I'm comfortable telling you to eat whole grains and fruits and vegetables and cut back on saturated fats,' Dr Blumberg said, 'even though we don't have clinical trials showing that.'


Conclusions of other studies

# The 10-year-long Women's Health Study found that women who took vitamin E were just as likely to develop heart disease, stroke and a variety of cancers as those who took a placebo.

# The Women's Antioxidant Cardiovascular Study tested the effects of vitamins C and E and beta carotene in women with signs of heart disease for an average of 9.4 years. None of the supplements had any effect.

# The Physicians' Health Study tested vitamins C and E in male doctors for an average of eight years and found the supplements did not make their hearts healthier.

# The Women's Health Initiative tracked women for an average of seven years and found that vitamin D plus calcium did not protect against invasive breast cancer.

# The Selenium and Vitamin E Cancer Prevention Trial tested those supplements in men for more than five years and found that they did not reduce the risk of prostate cancer.

[We all get some. Maybe it's enough. It's a billion dollar business.]

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