Burden of cancer attributable to never breastfeeding in Japan in 2015

We estimated the population attributable fraction (PAF) of cancers in Japan attributed to never breastfeeding in 2015. The data on breastfeeding in Japan were derived from two sources. Data on women aged younger than 40 were obtained from the Longitudinal Survey of Babies in the 21st Century (LSB21); those for women aged 40 to 69 was derived from the Japan Public Health Center-based Prospective Study for the Next Generation (JPHC-NEXT). For the present study, the optimal frequency of breastfeeding was a history of ever breastfeeding. The PAF was calculated for each age group using a standard formula. Overall, 0.3% of total cancer incidence and 0.1% of total cancer mortality in Japanese women were attributable to never breastfeeding. The high prevalence of women who breastfed children may explain the lower fraction of cancer attributable among Japanese women compared to studies from other parts of the world.