Do dairy foods, calcium intakes increase breast cancer risk?

Consumption of dairy foods or calcium does not appear to heighten the risk of breast cancer, while higher yogurt and cheese (cottage or ricotta) consumption shows an inverse correlation with the risk of oestrogen-receptor (OR) breast cancer, a less hormonally dependent subtype with poor prognosis, reveals a study.

Individual-level data of >1 million women who were followed for a maximum of 8–20 years were pooled across 21 cohort studies. The authors then assessed the associations for dairy product and calcium intakes with the risk of incident invasive breast cancer overall (n=37,861 cases) and by subtypes defined by OR status. Then, they estimated and combined study-specific multivariable hazard ratios (HRs) using random-effects models.

In general, the consumption of specific dairy foods, dietary (from foods only) calcium, and total (from foods and supplements) calcium was not associated with the risk of overall breast cancer.

Each dairy product exhibited a null or very weak inverse correlation with overall breast cancer risk (p_trend>0.05 for all), but intakes of yogurt and cottage/ricotta cheese were found to be inversely associated with OR-negative tumours only (≥60 g/d vs <1 g/d of yogurt: pooled HR, 0.90, 95 percent confidence interval [CI], 0.83–0.98; ≥25 g/d vs <1 g/d of cottage/ricotta cheese: pooled HR, 0.85, 95 percent CI, 0.76–0.95).

Additionally, dietary calcium intake showed a weak association with breast cancer risk (pooled HR per 350 mg/d, 0.98, 95 percent CI, 0.97–0.99).

“Future studies on fermented dairy products, earlier life exposures, OR-negative breast cancer, and different racial/ethnic populations may further elucidate the relation,” the authors said.