Content Validity of a Short Calcium Intake List to Estimate Daily Dietary Calcium Intake of Patients with Osteoporosis

Purpose: Calcium supplements are prescribed for prevention of osteoporotic fractures, but there is controversy whether excess of calcium intake is associated with cardiovascular events. While an accurate estimation of dietary calcium intake is a prerequisite to prescribe the adequate amount of supplementation, the most adequate tools for estimating intake are time-consuming. The aim of this study is to validate a short calcium intake list (SCaIL) that is feasible in daily clinical practice. Methods: Based on the food groups contributing most to daily dietary calcium intake and portion sizes determined in an earlier study, a three-item, 1-min SCaIL was designed. As a reference method, an extensive dietary history (DH) with specific focus on calcium-rich foods and extra attention for portion sizes was performed. Beforehand, a difference of ≥250 mg calcium between both methods was considered clinically relevant. Results: Sixty-six patients with either primary (n = 40) or secondary (n = 26) osteoporosis were included. On average, the SCaIL showed a small and clinically non-relevant difference in calcium intake with the DH: 24 ± 350 mg/day (1146 ± 440 vs. 1170 ± 485 mg, respectively; p = 0.568). Sensitivity and specificity of the SCaIL, compared to the DH, were 73 and 80%, respectively. However, in 50% of the individuals, a clinically relevant difference of ≥250 mg calcium was observed between both methods, while in 17% this was even ≥500 mg. Conclusions: The SCaIL is a quick and easy questionnaire to estimate dietary calcium intake at a group level, but is not sufficiently reliable for use in individual patients. Remarkably, the mean dietary calcium intake estimated by the DH of 1170 mg/day indicates that a large proportion of osteoporosis patients might not even need calcium supplementation, although more data are needed to confirm this finding.