Effect of Oral Calcium Supplementation on Insulin Sensitivity in Patients With Metabolic Syndrome

Background: Evidence from epidemiological research suggests that dietary calcium may protect against metabolic abnormality in populations at high risk. Observational studies show the relationship between dietary calcium intake and metabolic syndrome. However evidence for beneficial effect of elemental calcium supplementation on metabolic syndrome is limited. Aims: Present studydetermined whether oral calcium supplementation reduced insulin resistance in patients with metabolic syndrome or not. Methods; Hundred patients who have metabolic syndrome without diabetes mellitus, parathyroid disease, chronic renal failure, pregnancy and lactationwere randomly allocated to the group receiving 1500 mg/ day of elemental calcium as calcium carbonate for 8 weeks and the control group. The primary outcome was change in insulin resistance as measured by homeostasis model assessment of insulin resistance (HOMA-IR). Other outcomes were changes of serum free ionized calcium (FiCa) level with accompanying serum parathyroid hormone (PTH) level. Fasting serum glucose was measured by glucose oxidase method. Serum insulin and PTH level were measured by enzyme linked immunoassay. Total serum ionized calcium was analyzed by Atomic Absorption Spectrophotometry. Serum FiCa(mg/dl) level was calculated by using following formula = [6Ca-(K/3)]/(K+6). Results: Mean age of participants was 47.38±13.2 years in calcium supplement group (n = 50) and 49.46±12.9 years in control group (n=50). Mean body mass index was not significant different between two groups (30.91 ±4.23 vs 30.37 ± 4.62 kg/m(2)). More female were involved in both group, 72% vs 62% respectively. Baseline biochemical parameters of the participants between two groups were not significantly different. After 8 week intervention period, mean serum FiCa increased significantly from 2.64±1.19 mg/dl to 5.82± 5.59 mg/dl, p<0.0001, serum PTH decreased significantly from 57.88 ±17.05 pg/ml to 35.7±23.12 pg/ml, p<0.0001, HOMA-IR decreased significantly from 5.14 ± 3.71 to 2.94±1.51, p<0.0001. None of these parameters were significantly affected in control group. By comparing biochemical changes of calcium supplement group to control group, Mean (SEM) of paired difference changes were observed in serum FiCa level [3.18(0.81) vs 0.81(0.25)mg/dl, p<0.05], serum PTH level [22.18(3.24) vs 3.58(1.99)pg/ml, p<0.0001] and HOMA-IR [2.19(0.45) vs 0.43(0.21), p<0.05]. It indicated that elemental calcium supplementation not only reduced insulin resistance but also decompensated the higher level of PTH to normal range by replenishing FiCa significantly. Conclusion: Eight-week oral elemental calcium supplementation of 1500mg/day showed beneficial effect on insulin sensitivity in patients with metabolic syndrome.