Global Calcium Bioavailability

Calcium intake shortfalls are common worldwide, yet calcium adequacy is typically estimated from total calcium content without accounting for differences in bioavailability. As a result, the amount of calcium available for absorption across the global food supply remains unclear.

The objective of this study was to apply the Weaver et al. calcium bioavailability algorithm, which incorporates calcium load, phytate, and oxalate, to estimate bioavailable calcium in the global food supply, compare total and bioavailable calcium against recommended intakes, and identify regional differences in calcium adequacy.

Data from the Food and Agriculture Organization Food Balance Sheets were integrated with nutrient composition data from FoodData Central to estimate total and bioavailable calcium availability by country and region. Food Balance Sheets provide standardized national-level estimates of per capita food availability for human consumption; therefore, results reflect food supply availability rather than actual intake and do not account for dietary needs across life stages. Calcium, phytate, and oxalate values were mapped to food composition databases, adjusted for serving size, and used to calculate bioavailable calcium for individual foods. Country-level estimates were generated by summing daily per capita bioavailable calcium across foods.

The Weaver et al. calcium bioavailability algorithm was successfully applied to global food supply data, yielding an estimated mean calcium bioavailability of 30.7%, consistent with the general estimate that ∼30% of dietary calcium is absorbed. Predicted bioavailable calcium was lower than total calcium across all food categories, reflecting reduced absorption associated with calcium load and the presence of phytate and oxalate in the food supply. The greatest shortfalls in bioavailable calcium supply were observed in Africa and Southeast Asia, where predicted bioavailability was below recommended intakes for healthy adults.

These findings demonstrate that accounting for bioavailability can improve assessment of calcium adequacy and help identify regions where public health strategies are needed to improve access to bioavailable calcium.