Antioxidants, dietary supplements, vitamin pills – many people take them every day in the hope that they are good for their health.
But a new Danish study of all relevant trials carried out around the world shows that taking antioxidants in the form of vitamin A, E and beta-carotene is a risky business for us.
These antioxidants increase mortality – the risk of sudden death is higher for people who take these dietary supplements than for those who do not.
The results of this study have just been published in the scientific journal Cochrane Library.
“Our new study shows that these three antioxidants increase mortality by about four percent,” says Christian Gluud MD, a medical consultant and the head of the clinical research-based Copenhagen Trial Unit at the Copenhagen University Hospital, who led the study.
“So taking these pills is risky, and we would like to dissuade people who are healthy and who have a balanced diet from taking them.”
The newly published study confirms the results of a study in 2008 carried out by the same researchers.
The conclusions then were based on a statistical study of 68 randomised trials covering 232,606 people. Some were given dietary supplements in the form of antioxidants, while others were given either placebos as supplements or no supplements at all.
At the time, the researchers’ conclusion was the subject of a media storm – and hefty discussions in the research world, because many researchers working in the field of health, diet and supplements disagreed with the findings. The authorities chose not to intervene, and chemists and other shops are still selling dietary supplements.
The sceptics referred to studies that showed that people who take vitamin pills often have an unhealthy lifestyle because they believe that taking dietary supplements will improve their health in any case. In the sceptics’ opinion, this could explain the increased mortality among those who took the pills.
Gluud rejects this criticism:
“The higher mortality is seen in precisely these randomised trials, where dietary supplements were given to one group, while the other group got a placebo,” he says. “Neither of the groups knew whether they got a dietary supplement or a placebo. Therefore you can expect with confidence that any changes in lifestyle would be the same in the two groups.”
The researchers tested both single vitamins and multivitamins – and they found excess mortality in both cases.
Dietary supplements are taken by about 15 percent of the population in Europe and North America.
The new study was carried out in 2011 and is based on eleven new trials involving 64,157 other people.
The analyses show that the antioxidants increase mortality significantly with a comparative risk increase of four percent – the same result as in the earlier study.
“We found precisely the same effects as we did in the previous study, so now we feel even more confident about our conclusion,” says Gluud.
As yet, the researchers do not know the cause of the increased mortality, but they have some theories.
An antioxidant is a naturally occurring or synthetically produced substance that prevents or weakens oxidation that damages or destroys cells.
An antioxidant can be an enzyme or another organic molecule that counteracts the damaging effects of oxygen in living tissue.
The word is mainly applied to the molecules that inhibit the production of ‘free radicals’ – molecules with unpaired electrons.
“No new causes of death have been observed among those who died,” he says. “Our best explanation is therefore that these antioxidants have a toxic effect that accelerates normal ageing processes such as arteriosclerosis and cancer.”
Gluud is concerned that chemists and other shops are still selling the vitamin pills.
“The authorities and the chemists should take note of the new results and stop selling these pills as soon as possible,” he says.
Gluud emphasises that the findings do not apply only to dietary supplements containing vitamin A, E or beta-carotene in high doses that exceed the recommended daily intake.
“For the great majority of the people in the trials, the doses covered were within the recommended daily intake level,” he says. “In other words, it is quite ordinary doses that give the increased mortality.”
Read this article in Danish at videnskab.dk