Abstract
INTRODUCTION: The association between calcium (Ca) intake and incidence of type 2 diabetes mellitus (T2DM) remains still inconclusive. We investigated the association of total and food source-specific Ca intake and the incidence of T2DM in Iranian adults. METHODS: This cohort study was conducted on adult Iranian men and women (n = 2,458 subjects, mean age 39.3 ± 13.4 years, 1130 men (46%) and 1328 women (54%)), free of T2DM, who were assessed for Ca intake at baseline (2006-2008) and were followed up to 2018-2022. To evaluate potential non-linear associations between dietary calcium intake and T2DM risk, we employed univariate unrestricted regression spline analysis. Cox proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the risk of developing T2DM across quartiles and per each 100 mg/d of total and food-specific Ca intake. RESULTS: During the study follow-up, 353 subjects with T2DM were diagnosed. Mean daily Ca intake was 1,313 ± 526 mg/day, mainly from dairy and plant-based foods (51.62 and 40.08%, respectively), and the remaining from the processed and ultra-processed foods (UPFs) and animal sources (2.23 and 6.07%, respectively). Dairy sources contributed a Ca intake of 704 ± 393 mg/day. Higher intake of dietary Ca from plant-based foods (> 640 vs. <322 mg/day) was associated with a decreased risk of T2DM by 40% (HR = 0.60, 95% CI = 0.41-0.87). Conversely, higher Ca intake from processed and UPFs (> 100 vs. <28.6 mg/day) increased T2DM risk (HR = 1.53, 95%CI = 1.10-2.13). Furthermore, each 100 mg/day increase in dietary Ca from processed and UPFs raised the risk of T2DM (HR = 1.26, 95% CI = 1.04-1.52). Intake of Ca from dairy was not associated with the incidence of T2DM (HR = 0.98, 95% CI = 0.95-1.01). CONCLUSION: A higher intake of dietary Ca from plant-based foods shows an inverse association with risk of T2DM. Conversely, increased consumption of Ca from processed and UPFs seems to be a risk factor for developing T2DM. These findings suggest that the source of dietary Ca may play a significant role in T2DM risk, highlighting the importance of food choices in managing health outcomes.