Micronutrients and breast cancer.

A large part of the epidemiological debate on diet and breast cancer has been dominated by the issue of whether fat, particularly animal fat, increases risk. Lately, the possible protective effect of various dietary constituents has received more attention. Vitamins C and E, and beta-carotene have antioxidant activity and may thus provide a cellular defence against reactive oxygen species that damage DNA. Dietary fibre may influence oestrogen metabolism. A large case-control study (2,569 breast cancer and 2,588 hospital controls) conducted in six Italian areas between 1991 and 1994 suggested that a diet rich in several micronutrients was associated with significantly lowered risk. After allowance for non-dietary risk correlates, energy intake and the mutual confounding effect of the various micronutrients, beta-carotene, vitamin E and calcium were associated with odds ratios in the highest intake quintile compared to the lowest one of 0.84, 0.75 and 0.81, respectively. Among different types of fibre, only cellulose intake showed a moderate inverse association. Evidence from other studies suggests that a favourable role of some micronutrients is possible, albeit probably less important than for cancers of the stomach and colon-rectum. Indeed, the relationship between fruit and vegetable intake is also less marked/consistent for breast cancer than for other sites. Among agents that have only recently been investigated, isoflavones, which are weak oestrogens, are of particular interest.