Vitamin supplements may cause cancer

Vitamin supplements may increase the chances of dying from cancer, a science review finds. And the studies, which compared the health of people who regularly took antioxidant pills with those who took dummy pills, suggest that combinations of beta-carotene with either vitamin A or vitamin E pose the most risk.
The findings, published in the Lancet medical journal, go further than recent evidence that such pills do no good, and, if confirmed, could severely damage the vitamin industry worldwide.
However, the research review warns against drawing conclusions from work that does not yet provide “convincing proof of hazard”.
Covering trials involving more than 170,000 people, the review echoed other studies that found no protective effect from vitamins against disease.
Results from a five-year study of people at high risk of vascular disease, published two years ago, found vitamins provided no significant reduction in the risk of heart attacks, stroke, cancer, or other health problems.
But the new work has found tentative evidence indicating that extra selenium might protect against gastrointestinal cancers.
The human diet is a mix of oxidants and antioxidants, and an increase in too many oxidants can cause cancer by inducing gene mutations.
The Lancet review was conducted by Goran Bjelakovic, of the University of Nis, Serbia and Montenegro, and colleagues of the Cochrane Hepato-Biliary Group. Fourteen studies tracked people who had taken vitamins regularly between one and 12 years. Overall their results suggested no protective effect for oesophageal, gastric, colorectal, pancreatic or liver cancer. There was a small increase of 6% in relative risk, in comparisons of deaths among those taking supplements with those linked to dummy pills. The increase in relative risk was higher (10%) for those on a combination of beta-carotene and vitamin A, and was at 30% for those on a combination of beta-carotene and vitamin E.
Four of the trials suggested a reduced risk for those taking selenium, but there may have been shortcomings in the research, said the review team.
Dr Bjelakovic said: “We could not find evidence that antioxidant supplements can prevent gastrointestinal cancers. On the contrary, they seem to increase overall mortality. The potential preventive effect of selenium should be studied in adequate randomised trials.”
David Forman from Leeds University and Douglas Altman noted that the researchers had estimated that if their findings were correct 9,000 people among every million users of such supplements would die prematurely. “The prospect that vitamin pills may not only do no good but also kill their consumers is a scary speculation, given the vast quantities used in certain communities.”
But they said the analysis of mortality was “work in progress” and did not “offer convincing proof of hazard”.
They added: “In the event that a hazard is established ... these researchers will need to identify which specific interventions are associated with any risk. It is unlikely that all supplements will exert a similar effect and it will be vital to establish the safety profile for those with demonstrated benefits.”
Other studies had suggested a benefit from antioxidants.

Guardian