Summary.-Mean, age-standardized breast-cancer mortality rates for women of 41 countries, during 1970-71, were closely correlated with diet for 1964-66. Partial correlation analysis indicated that breast-cancer rates were positively correlated with total fat, animal protein and animal calories, independently of other components of diet. These 3 components were correlated with one another so closely that it was not possible, with available data, to say whether any one was associated with breast cancer independently of the other 2. In addition to, and independently of, these correlations, breast cancer was associated with consumption of refined sugar.Breast-cancer mortality rates at 50-54 years during 1964-67 for 26 countries were closely correlated with childbearing, expressed as mean family size for women aged 45-49 years in 1960-61. However, this correlation was not independent of the correlations with diet, and it was concluded that variation of breast-cancer rates between countries arose predominantly from differences in diet. The variation of breastcancer risk with childbearing, observed in clinial studies, seemed best regarded as a second gradient of risk, seen more readily as variation of breast-cancer rates within a population, where differences in diet would be relatively small. The physiological basis for the association between breast cancer and diet was not clear. The dietary associations did not correlate in an obvious way with height, obesity and oestrogen levels, factors observed in clinical studies to influence risk of breast cancer. That the observed statistical associations were real was supported by published findings on effects of diet on mammary cancer in experimental animals, as well as the lower rates of breast cancer amongst vegetarians.
SUMMARY.-International rates of breast cancer for females aged 40-44 years (the " early " rate) and for females aged 65-69 years (the " late " rate) were positively correlated with sugar and fat intakes. The correlation explained three-quarters of the variation in the late rate, for 22 countries, but only half of the variation in the early rate. The late rate was, further, positively correlated with estimates of the percentage of nulliparous women (9 populations) and, together with terms for sugar and fat intakes, the multiple regression explained 90ev of the variation. Early registration rates (13 populations) were positively correlated with blood group A which appeared, from the multiple regression equation, to contribute more than twice the amount to the early rate than did sugar and fat intakes. The contribution of blood group A to the late rate appeared to be only one-third of that for sugar and fat intakes.DE WAARD (1969) has recently reviewed evidence for two age distributions of breast cancer. From their clinical characteristics (de Waard, de Laive and Baanders-van Halewijn, 1960) it was reasonable to regard breast cancer rates at age 40-44 years as a measure of the early group, while the late group could be represented by rates at 65-69 years. The. present study is an analysis of the epidemiological characteristics of these two rates. AIETHOD AND RESULTS DataData for different countries were examined for associations between breast cancer rates at 40-44 years, and at 65-69 years, with diet, parity, birth rate and blood group A. The data were as follows:Breast cancer mortality.-Mean rates for females aged 40-44 years and 65-69 years were calculated for the period 1962-66 (Segi and Kurihara, 1966; Segi, Kurihara and Matsuyama, 1969) Fig. 1).Diet. Mean annual per capita intakes (United Nations, 1950-65) of total calories, total carbohydrate, sugar, fat and meat were calculated for the period
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