Do dairy products increase breast cancer risk?

Women who regularly consume dairy products do not have an increased risk of developing breast cancer, reveals a study. However, there is heterogeneity seen for the type of dairy food, period of life, and tumour subtypes.

A team of investigators analysed data from 63,847 women in the Nurses’ Health Study collected from 1980 to 2018. Using validated semiquantitative food frequency questionnaires, they assessed the average intake of dairy products during adulthood throughout follow-up. The participants recalled their adolescent dietary intake in 1986.

Hazard ratios (HR) for the association of dairy product intake with overall breast cancer risk were estimated using multivariable Cox proportional hazards models. HRs were also measured by menopausal status and by subtypes.

A total of 5,733 incident cases of invasive breast cancer were recorded during 32 years of follow-up (n=5,298 postmenopausal). Breast cancer risk showed no significant association with lifetime, adolescent, adulthood, and postmenopausal total dairy and milk consumption (HR comparing highest with lowest quintile range, 0.97‒1.08).

A potential positive association, however, was observed between adolescent milk intake and breast cancer risk (HR, 1.09, 95 percent confidence interval [CI], 1.00‒1.18).

Notably, higher lifetime and premenopausal consumption of cheese might even help to reduce the risk of developing breast cancer (highest vs lowest quintile: HR for lifetime cheese intake, 0.90, 95 percent CI, 0.82‒0.98; HR for premenopausal cheese intake, 0.89, 95 percent CI, 0.79‒1.00).

In addition, “[r]esults varied by tumour subtype, and some evidence for heterogeneity was observed for an association between premenopausal milk intake and breast cancer (HR for oestrogen receptor [ER]-positive, 0.84, 95 percent CI, 0.72‒0.99; HR for ER-negative, 1.36, 95 percent CI, 1.00‒1.84; p=0.04 for heterogeneity).