Vitamin E supplementation raised chances of new cancer in at-risk patients
them from a recurrence of the disease were actually at higher risk
of getting a second cancer while taking the supplement than those
in a placebo group, researchers reported yesterday.
While the risk returned to the same level as the placebo group once patients had stopped taking the vitamin, the findings may raise consumer concerns about taking high-dose (400IU daily) vitamin E.
A number of studies published in recent years have already demonstrated potential adverse effects of taking high-dose alpha-tocopherol supplements, causing a knock-on effect in the supplement industry, particularly in the US.
In an interview earlier this week, Dr Martin Jager, head of human nutrition at BASF, said there was still "a little hesitance" over the vitamin in the US, following a meta-analysis on vitamin E at the end of 2004 and last month's results from the Hope-Too trial.
However the Canadian researchers warned that the new study was carried out on patients at high risk of cancer and therefore not representative of the general population.
"There is some concern about the generalization of the study results to individuals in the general population who are at low risk of a first cancer. Nevertheless, our results suggest that caution should be advised regarding the use of high-dose vitamin E supplements for cancer prevention," said author Dr Isabelle Bairati, professor at Canada's Universite Laval Faculty of Medicine and researcher at Hotel-Dieu de Quebec's Oncology Research Centre.
In addition, the fact that the risk of secondary cancers dropped again once supplementation stopped suggests that the vitamin may have merely had a screening effect, leading to earlier detection of cancers.
The trial, published in yesterday's issue of the Journal of the National Cancer Institute (vol 97, no 7, pp481-488), was carried out on 540 people that had been treated for early stage head and neck cancer and were at high risk of developing another cancer.
Half of the participants took 400 international units of alpha-tocopherol daily for three years while the rest were given a placebo. Some participants were also initially given beta-carotene supplements but this arm of the study was stopped early after another trial linked the nutrient to raised risk of lung cancer.
During the three-year period, 20 per cent of the patients taking vitamin E developed cancer as opposed to only 10 per cent in the placebo group.
However once supplementation had been stopped, the situation was reversed: more cancer cases were recorded in the placebo group than in the vitamin E group.
After eight years, the percentage of patients who developed cancer was the same in both groups (30 per cent).
The authors suggest that the use of vitamin E supplements may have sped up the development of latent cancers in this group.
Researchers have theorized that the lower risk of cancer among people with a high fruit and vegetable intake may be the result of these foods' antioxidant vitamins. However studies investigating whether antioxidant supplements, such as vitamin E, can also confer this benefit have provided conflicting results.
A major trial is currently testing the effects of vitamin E and selenium on risk of prostate cancer in 34,000 men. These results could prove highly influential in the debate surrounding vitamin E and cancer prevention.
