Associations between breast-cancer mortality rates, child-bearing and diet in the United Kingdom.

Changes of breast-cancer (BC) mortality for all women in England and Wales between 1911 and 1975, and for the social-class gradient during the 1950s, were not related to changes in child-bearing. The changes in BC mortality for all women were associated with changes in consumption of fat, sugar and animal protein 1-2 decades earlier. A decline in mortality around 1935 was not obviously related to changes in fat or sugar, but dietary data were sparse. The social-class gradient of BC mortality almost disappeared during the 1950s; rates declined for the upper classes but increased for the lower. These opposite changes could have resulted from the opposite changes in diets of the upper and lower classes which occurred in the early 1940s. In contrast, the geographical variation of BC mortality within the United Kingdom, by region or by urban-rural aggregate area, was closely correlated with child-bearing but poorly correlated with diet. The poor correlation with diet might be a consequence of the small range of variation of diet between regions of the United Kingdom. The regional gradient of BC mortality was low in 1961, a decade after the period of food rationing when regional variation in diet would have been reduced. This suggested that diet did contribute to the regional variation of BC mortality within the United Kingdom, perhaps jointly with contributions from child-bearing.