Effect of different doses vitamin D and calcium supplementation on blood glucose and insulin sensitivity in middle-aged and elderly patients with impaired glucose tolerance

Abstract

Objective To explore the effect of different doses of vitamin D (VitD) and calcium supplementation on blood glucose and insulin sensitivity in middle-aged and elderly patients with impaired glucose tolerance (IGT). Methods A total of 150 individuals with IGT [aged (57±4) years] were chosen during physical examination from January 2013 to May 2015, of which 80 cases were male and 70 were female. They were randomly divided into three groups: regular dose group (group A, n=49, VitD 125 U/d + calcium 600 mg/d), double dose group (group B, n=51, VitD 250 U/d + calcium 1 200 mg/d), and control group (group C, n=50, no medication). Oral glucose tolerance test (OGTT) was performed before and after VitD and calcium supplementation. Blood biochemical parameters were measured. Homeostasis model assessment (HOMA) insulin resistance index (HOMA-IR) and HOMA islet β-cell function index (HOMA-β) were calculated. Comparison of means was done by one-way analysis of variance (ANOVA). LSD-t test was used when P<0.05 as the limit for statistical significance.appropriate. Correlation analysis was performed using Pearson correlation analysis and multiple stepwise regression analysis. Results (1) Compared with group C, fasting plasma glucose (FPG), 2-hour plasma glucose (2hPG) and insulin (2hINS), glycated hemoglobin A1c (HbA1c), HOMA-IR in group A and B declined significantly (P<0.05) after 6 and 12 months of VitD and calcium treatment, while the level of serum 25(OH)D and HOMA-β were dramatically increased (all P<0.05). (2) After 6 and 12 months treatment, HbA1c, HOMA-IR significantly declined from baseline [HbA1c: (5.9±0.5)%,(5.9±0.6)%; HOMA-IR:(3.8±0.9, 3.7±0.7)] in group A [HbA1c:(5.7±0.2)%, (5.6± 0.6)%; HOMA-IR: 3.6±1.1, 3.4±1.5] and group B [HbA1c:(5.7±0.6)%,(5.5±0.4)%; HOMA-IR: 2.8±1.5 vs 2.0±1.2] (all P<0.05). And the levels of FPG and 2hPG were also reduced. The differences were significantly (all P<0.05). (3) In addition, FINS, 2hINS, HbA1c and HOMA-IR in 12 months after treatment were declined in group B compared with group A, while the level of serum 25(OH)D in group B was increased [(40±5) vs (32±6) μg/L] (all P<0.05).(4) Pearson correlation coefficient analysis showed that serum 25(OH)D in 12 months post-treatment was positively correlated with HOMA-β (r=0.210), serum calcium (r=0.444) (both P< 0.05); while was negatively correlated with HbA1c(r=- 0.241), FPG (r=- 0.215) and HOMA-IR (r=- 0.225) (P<0.05). Multiple regression analysis indicated that serum 25(OH)D in patients with IGT was markedly positively correlated with HbA1c(r=2.138) VitD doses (r=7.160 for regular-dose, 7.330 for double dose) and total cholesterol (r=2.319) (P<0.05). Conclusion Vitamin D and calcium supplementation can improve blood glucose and insulin sensitivity in middle-aged and elderly patients with IGT, in a dose and time dependent manner. Key words: Vitamin D; Calcium; Impaired glucose tolerance; Insulin sensitivity