# Association between being breastfed in infancy and adult colorectal cancer risk among Japanese men and women

## TL;DR

This study found no overall link between being breastfed as an infant and adult colorectal cancer risk in Japan, but some sex and birth year differences were observed.

## Contribution

The study provides new insights into the potential sex- and birth year-specific associations between breastfeeding and adult colorectal cancer risk in Japan.

## Key findings

- No overall association was found between breastfeeding and colorectal cancer risk.
- Women born after 1950 who were breastfed showed a non-significant increased risk of colorectal cancer and benign tumors.
- Men born after 1950 who were breastfed had a significantly decreased risk of benign tumors.

## Abstract

It has been postulated that being breastfed in infancy affects not only health status in childhood but also disease risk in adulthood. To investigate the association of being breastfed with the risks of adult colorectal cancer and benign tumor, we conducted a case–control study including 1190 colorectal cancer and 1585 benign tumor cases and 5301 controls, admitted to a single hospital in Miyagi Prefecture, Japan, between 1997 and 2013. History of having been breastfed was assessed using a self-administered questionnaire, and odds ratios (ORs) were estimated using unconditional logistic regression. There was no association between being breastfed and colorectal cancer risk (breastfed versus formula-only fed, OR = 1.21; 95% CI 0.87–1.67). There was also no association with the risk of benign tumor (OR = 1.04). On the other hand, analyses stratified by sex and birth year found heterogeneous associations. Women born after 1950 who had been breastfed tended to have increased risks of colorectal cancer (OR = 1.58) and benign tumor (OR = 1.51) relative to those who had been formula-only fed, although not statistically significant. In men born after 1950, being breastfed was associated with a significantly decreased risk of benign tumor (OR = 0.57; 95% CI 0.33–0.98).