The link between a family history of breast cancer and a woman's likelihood of developing the disease is smaller than suggested earlier, according to American research.

Earlier studies have suggested that there is a strong correlation which has been enough to prompt some doctors to suggest that women in supposedly high risk groups should have "prophylactic mastectomies" to avoid developing the disease.

However, a study of 117,988 women aged 30 to 55 found that the "risk associated with a mother or sister history of breast cancer is smaller than suggested by earlier retrospective studies. Overall, within this population of middle aged women, only 2.5 per cent of breast cancer cases are attributable to a positive family history."

They suggest that the size of the increased risk identified in earlier studies may in part be explained by "heightened awareness or over reporting of family history by patients with breast cancer, whereas control patients may be less aware of all breast cancer diagnoses in their family." JAMA, 21 July 1993.

Meanwhile, researchers in the US suggest that vitamin A may act as a preventative against breast cancer. They looked at nearly 90,000 nurses and, after adjustment for risk factors, found that "women in the top 20 per cent for dietary vitamin A intake were significantly less likely to develop breast cancer than the women in the bottom 20 per cent." Even those with little vitamin A in their diets but who took it in supplement form were also at reduced risk.

No clear benefit was identified from vitamins C or E; but women who consumed more vegetables had a lower breast cancer risk.