Diet and the risk of breast cancer in a case-control study: Does the threat of disease have an influence on recall bias?

It has been suggested that recall bias may explain the discrepant results b etween case-control and cohort studies on diet and the risk of breast cance r. Two control groups were used for this case-control study of 25 to 75-yea r old breast cancer cases (n = 310). The first group consisted of populatio n controls drawn from the Finnish National Population Register (n = 454). T he second group consisted of women who were referred to the same examinatio ns as were the cases because of clinical suspicion of breast disease but wh o were later diagnosed as healthy (referral controls; n = 506). Because the diagnosis was unknown at the time of interview, it was possible to assess by comparing the two control groups whether the self-reporting of diet chan ged under the threat of disease. Dietary habits were examined using a valid ated, self administered food-frequency questionnaire. Premenopausal women m isreported their consumption of liquid milk products, tea, and sugar. Repor ting bias was also associated with the intake of fat and vitamins. Postmeno pausal women misreported consumption of milk products. When recall bias was taken into consideration, milk was associated with increased risk of preme nopausal breast cancer, whereas high consumption of poultry or high intake of monounsaturated fatty acids, n-3 fatty acids, n-6 fatty acids, and vitam in E were related to lower risk. The study suggested that oil, milk, cheese , coffee and beta-carotene may act as protective factors in postmenopausal women, whereas butter and cream may be risk factors for breast cancer. In s ummary, it is possible that some food items may be overreported or underrep orted under the threat of disease in health conscious population. However, most of the results in this study were not modified by recall bias. I CLIN EPIDEMIOL 52;5:429-439, 1999. (C) 1999 Elsevier Science Inc.