Older women who eat a lot of carbohydrates may be at increased risk of a less common but deadlier form of breast cancer, a new study suggests.
The findings, from a study of nearly 335 000 European women, hint at a potential link between glycaemic load and oestrogen-receptor-negative breast cancers. In this study, postmenopausal women with high glycaemic load diets had a 36% higher risk of ER-negative breast cancer, compared with women whose diets had the lightest load.
In general, diets with high glycaemic loads "have been associated with many negative health outcomes," noted Christina Clarke, a research scientist at the Cancer Prevention Institute of California in Fremont, and a consulting assistant professor at Stanford University. So although the current findings do not prove cause-and-effect, they can give women another reason to make healthier diet choices, according to Clarke, who was not involved in the study.
From a scientific standpoint, Clarke said the results are interesting because so little is known about what causes ER-negative breast cancers.
The current findings hint at a role for insulin pathways in ER-negative breast cancer, according to Clarke. "But there's definitely more work that needs to be done," she said.
The findings, which appeared online in the American Journal of Clinical Nutrition, are based on a long-running European study on nutrition factors and cancer risk. Of nearly 335 000 women in the study, 11 576 developed breast cancer over a dozen years. Overall, there was no link between breast cancer risk and glycaemic load - estimated from diet questionnaires the women completed at the study's start.
But the picture changed when the researchers focused on postmenopausal women with ER-negative cancer. Among women in the top 20% for glycaemic load, there were 158 cases of breast cancer, versus 111 cases in the bottom quintile. When breast tumours also lacked progesterone receptors, the gap was a bit more pronounced.
Still, the numbers "weren't huge," Clarke noted. And there are many other factors that could be different between those groups of women, although the study did account for some of them, including weight, exercise habits, calorie intake and smoking.
But, Clarke added, while no single factor accounts for breast cancer risk, the findings do offer more incentive to limit refined carbs in favour of healthier foods.
(Reuters Health, Amy Norton, July 2012)
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