A prospective cohort study produces inconclusive results in linking dietary calcium intake to overall and specific causes of mortality

Dietary calcium's role in human health and disease prevention is inconclusive. We examined the associations between dietary calcium intake and the risk of overall and specific causes of mortality. A prospective cohort study was performed for 42,146 individuals from 2008 to 2019. Face-to-face interviews used structured semi-quantitative food frequency and demographic lifestyle questionnaires to obtain calcium intake. The cause of 2,494 deaths was determined from medical records. We calculated hazard ratios (HR) and corresponding 95% confidence intervals (95% CI) using a Cox proportional hazards model across eight quantiles of dietary calcium intake. Compared to the reference range 222.5-261.3 mg/day, the lowest dietary calcium intake was associated with an increased mortality risk from all causes, HR (95% CI): 1.22 (1.04, 1.42). In contrast, the highest dietary calcium intake was associated with an increased risk of cancer death, HR (95% CI): 1.43 (1.01, 2.01). By stratified analysis, the lowest dietary calcium intake was associated with an increased risk of mortality from all causes in women, in never smokers, individuals with a BMI < 23 kg/m², never drinkers, no diabetes, no history of hypertension, and no history of cancer. An increased risk of overall mortality and cancer death at the borderline was observed for the lowest and highest calcium intake, respectively. There is a possible U-shaped association between calcium intake and the risk of all causes and cancer. The reference group ranges from 222.5 mg/day to 261.3 mg/day. The findings warrant further research on the association between dietary calcium intake and overall mortality and cancer.