Writing in Cancer Causes and Control, US scientists report that for every 1,000 microgram increase per 1,000 kcal of diet of beta-carotene was associated with a 12 per cent reduction in the risk of endometrial cancer.
Similarly, for every 50 milligram increase per 1,000 kcal of vitamin C the risk of endometrial cancer was reduced by 15 per cent, and for every 5 milligram increase per 1,000 kcal of vitamin E the risk of endometrial cancer was reduced by 9 per cent.
Endometrial cancer is the fifth most common cancer among women worldwide - around 7,000 American women die from the disease annually - but incidence of the cancer varies more than 10-fold worldwide.
The results are based on data from 12 case-control studies, and intakes from supplements were not considered by the researchers, led by Elisa Bandera from the Cancer Institute of New Jersey.
“Although the current case-control data suggest an inverse relationship of endometrial cancer risk with dietary intakes of beta-carotene, vitamin C, and vitamin E from food sources, additional studies are needed, particularly cohort studies, to confirm an association,” cautioned the researchers.
Indeed, data from one prospective cohort study “provided little indication of an association”, said Bandera and her co-workers.
Commenting on the potential mechanism, the US-based researchers noted that antioxidant vitamins may reduce the risk of cancer by limiting oxidative damage to DNA.
A vast body of epidemiological studies has linked increased dietary intake of antioxidants from fruits and vegetables to reduced risks of a range of diseases including cancer, cardiovascular disease and diabetes.
However, when such antioxidants have been extracted and put into supplements the results, according to the randomized clinical trials (RCTs), do not always produce the same benefits, and may even be harmful.
These observations have led to much negative publicity about antioxidant supplements, particularly the more well-known vitamin E and beta-carotene.
The design of randomised clinical trials, following the drug- or evidence-based model has received much criticism.
In an editorial comment in the Journal of the American Medical Association, Peter Gann, MD, ScD, from the University of Illinois at Chicago, said: “...single-agent interventions, even in combinations, may be an ineffective approach to primary prevention in average-risk populations.”
Bandera worked in collaboration with scientists from the University of Medicine and Dentistry of New Jersey, the American Cancer Society, and Kaiser Permanente
Source: Cancer Causes and Control July 2009, Volume 20, Number 5, Pages 699-711doi: 10.1007/s10552-008-9283-x“Antioxidant vitamins and the risk of endometrial cancer: a dose-response meta-analysis” Authors: E.V. Bandera, D.M. Gifkins, D.F. Moore, M.L. McCullough, L.H. Kushi