Risk factors for breast cancer by age and menopausal status: a case-control study in Singapore

Abstract

A case-control study was conducted among Singapore Chinese women, comprised of 200 histologically confirmed cases of breast cancer and 420 hospital controls. Subjects were interviewed on family history of breast cancer, social and demographic characteristics, reproductive history, and diet one year prior to interview. Differences in risk factors were observed according to menopausal status. In the premenopausal group, the most consistently significant nondietary effect was an increased risk with late age at first birth. In postmenopausal women, the most consistent nondietary effects were increased risks with nulliparity, tall stature, high educational status, and a family history of breast cancer. In premenopausal women, the strongest dietary effects were low risks with high intakes of polyunsaturated fatty acids (PUFA), beta-carotene, soya protein as a proportion of all protein, and a high risk with high red-meat intake. No dietary effects were observed in postmenopausal women. Examination of effects by 10-year age groups suggested that the differences in the effects of age at first birth, nulliparity, height, education, beta-carotene intake, and PUFA intake between premenopausal and postmenopausal women were at least partly attributable to age-related differences in the baseline distributions of these variables. The variation in the effects of red meat and soya protein appeared to be attributable mainly to menopausal status itself, which is consistent with the hypothesis that these factors operate on risk by way of hormonal mechanisms.

Dietary and other risk factors in women having fibrocystic breast conditions with and without concurrent breast cancer: A nested case‐control study in Shanghai, China

“…Alternatively this possible emergence of an association in a recent study in China could be due to greater variability in soy consumption in recent years as more people adopt a less traditional diet, with some reducing their soy intake below a threshold level needed to provide protection against breast cancer. This hypothesis is consistent with results from studies of Asians living in the United States, 48,49 and of Chinese in Singapore, 50,51 where a mixture of traditional and western diets predominates, that showed evidence for a protective effect of soy against breast cancer. The results of our study are also supportive of this hypothesis.…”

A prospective study of vegetarianism and isoflavone intake in relation to breast cancer risk in British women

“…45,46 Two early studies found evidence for a protective effect of soy food intake in premenopausal but not among postmenopausal women. 29,47 However, findings from other studies of isoflavone intake in pre-and postmenopausal women separately have been inconsistent, 9,10,12,43,44,48 with most reporting no significant association, as was found in the current study. Since HRT use may mask or alter any association of isoflavone intake with breast cancer risk, we repeated the analysis for women who were not using HRT, but still observed no significant relationship between isoflavone intake and risk for breast cancer.…”

“…Two early case-control studies in predominantly Asian populations suggested that a high intake of soy food may be protective against breast cancer in women. 29,30 Since plasma concentrations of isoflavones in postmenopausal women who consume soy foods are up to 1,000 times higher than those of oestradiol, and phytoestrogens are structurally similar to endogenous oestrogens, it has been suggested that such an association This factor is unknown for some women-these ''unknowns'' are excluded from the calculations of percentages. may exist because isoflavones may have an anti-oestrogenic effect.…”

Vitamins A, C and E and the risk of breast cancer: results from a case-control study in Greece

“…The reasons for this are not clear, but the proximity of younger women to the aetiologically relevant time period is a possible explanation. Several previous studies have considered differences by menopausal status in the effect of micronutrients (La Vecchia et al, 1987;Katsouyanni et al, 1988;Marubini et al, 1988;Rohan et al, 1988;Howe et al, 1990;Richardson et al, 1991;Zaridze et al, 1991;Lee et al, 1992;Hunter et al, 1993;Rohan et al, 1993;Yuan et al, 1995), but with inconsistent results. Approximately half of all studies reporting results by menopausal status indicate no differences in pre-and postmenopausal women (La Vecchia et al, 1987;Katsouyanni et al, 1988;Marubini et al, 1988;Rohan et al, 1993;Yuan et al, 1995).…”