Background: Few interventions directly compare equivalent calcium and vitamin D from dairy vs. supplements on the same bone outcomes. The radioisotope calcium-41 ((41)Ca) holds promise as a tracer method to directly measure changes in bone resorption with differing dietary interventions.
Objective: Using (41)Ca tracer methodology, determine if 4 servings/day of dairy foods results in greater (41)Ca retention than an equivalent amount of calcium and vitamin D from supplements. Secondary objective was to evaluate the time course for the change in (41)Ca retention.
Methods: In this crossover trial, postmenopausal women (n = 12) were dosed orally with 100 nCi of (41)Ca and after a 180 day equilibration period received dairy (4 servings/day of milk or yogurt; ~ 1300 mg calcium, 400 IU cholecalciferol (vitamin D3/day)) or supplement treatments (1200 mg calcium carbonate/day and 400 IU vitamin D3/day) in random order. Treatments lasted 6 weeks separated by a 6 week washout (WO). Calcium was extracted from weekly 24 h urine collections; accelerator mass spectrometry (AMS) was used to determine the (41/40)Ca ratio. Primary outcome was change in (41/40)Ca excretion. Secondary outcome was the time course for change in (41)Ca excretion during intervention and WO periods.
Results: The (41/40)Ca ratio decreased significantly over time during both treatments; there was no difference between treatments. Both treatments demonstrated a significant retention of (41)Ca within 1-2 weeks (p = 0.0007 and p < 0.001 for dairy and supplements, respectively). WO demonstrated a significant decrease (p = 0.0024) in (41)Ca retention within 1-2 weeks, back to pre-intervention levels.
Conclusion: These data demonstrate that urinary (41)Ca retention is increased with an increase in calcium and vitamin D intake regardless of the source of calcium, and the increased retention occurs within 1-2 weeks.
Keywords: 41Ca; 41Ca, calcium-41; AI, adequate intake; AMS, accelerator mass spectrometry; ANOVA, analysis of variance; BAP, bone specific alkaline phosphatase; BMC, bone mineral content; BMD, bone mineral density; BMI, body mass index; CTx, serum C terminal telopeptide of type 1 collagen; CV, coefficient of variation; Calcium supplement; DXA, dual energy X-ray absorptiometry; Dairy; ELISA, enzyme linked immune-sorbent assay; HCl, hydrochloric acid; Kinetic model; NDSR, Nutrition Data System for Research; NH4OH, ammonium hydroxide; PTH, parathyroid hormone; Postmenopausal; RCT, randomized controlled trial; RDA, recommended dietary allowances; WHNRC, Western Human Nutrition Research Center; nCi, nanocurrie; qCT, quantitative computed tomography.