Prevention of urinary tract infections with vitamin D supplementation 20,000 IU per week for five years. Results from an RCT including 511 subjects.

BACKGROUND: In observational studies vitamin D deficiency is associated with increased risk of infections, whereas the effect of vitamin D supplementation in randomized controlled trials is non-conclusive. METHODS: Five hundred and eleven subjects with prediabetes were randomized to vitamin D3 (20,000 IU per week) versus placebo for five years. Every sixth month, a questionnaire on respiratory tract infections (RTI) (common cold, bronchitis, influenza) and urinary tract infection (UTI) was filled in. RESULTS: Mean baseline serum 25-hydroxyvitamin D (25(OH)D) level was 60 nmol/L. Two hundred and fifty-six subjects received vitamin D and 255 placebo. One hundred and sixteen subjects in the vitamin D and 111 in the placebo group completed the five-year study. Eighteen subjects in the vitamin D group and 34 subjects in the placebo group reported UTI during the study (p < 0.02), whereas no significant differences were seen for RTI. The effect on UTI was most pronounced in males. The effect of vitamin D on UTI was unrelated to baseline serum 25(OH)D level. CONCLUSION: Supplementation with vitamin D might prevent UTI, but confirmatory studies are needed.

Vitamin D 20,000 IU per Week for Five Years Does Not Prevent Progression From Prediabetes to Diabetes.

CONTEXT: Vitamin D deficiency is associated with insulin resistance and risk of future diabetes. OBJECTIVE: The objective of the study was to test whether supplementation with vitamin D to subjects with prediabetes will prevent progression to type 2 diabetes mellitus (T2DM). DESIGN: This was a randomized controlled trial performed in 2008 through 2015. SETTING: The study was conducted at the clinical research unit at a teaching hospital. PATIENTS: Five hundred eleven subjects (mean age 62 y, 314 males) with prediabetes diagnosed with an oral glucose tolerance test as part of the Tromsø Study 2007­2008 were included. A total of 256 were randomized to vitamin D and 255 to placebo. Twenty-nine subjects in the vitamin D and 24 in the placebo group withdrew because of adverse events. INTERVENTIONS: Interventions included vitamin D (cholecalciferol) 20 000 IU/wk vs placebo for 5 years. Annual oral glucose tolerance tests were performed. MAIN OUTCOME MEASURE: Progression to T2DM was the main outcome measure. Secondary outcomes were change in glucose levels, insulin resistance, serum lipids, and blood pressure. RESULTS: The mean baseline serum 25-hydroxyvitamin D level was 60 nmol/L (24 ng/mL). One hundred three in the vitamin D and 112 in the placebo group developed T2DM (hazard risk 0.90; 95% confidence interval 0.69­1.18, Cox regression, P = .45, intention to treat analysis). No consistent significant effects on the other outcomes were seen. Subgroup analyses in subjects with low baseline 25-hydroxyvitamin D yielded similar results. No serious side effects related to the intervention were recorded. CONCLUSIONS: In subjects without vitamin D deficiency, vitamin D supplementation is unlikely to prevent progression from prediabetes to diabetes. Very large studies with inclusion of vitamin D-deficient subjects will probably be needed to show such a putative effect. This study tested if supplementation with vitamin D to subjects with prediabetes will prevent progression to type 2 diabetes (T2DM).

Effects of vitamin D binding protein phenotypes and vitamin D supplementation on serum total 25(OH)D and directly measured free 25(OH)D.

OBJECTIVE: To determine the relationship between serum total 25-hydroxyvitamin D (25(OH)D), directly measured free 25(OH)D and calculated free 25(OH)D with regard to vitamin D-binding protein (DBP) phenotypes, sex, BMI, age and season, and their interrelationship to vitamin D supplementation. DESIGN, PATIENTS AND INTERVENTIONS: A randomized controlled trial with 20 000 IU of vitamin D3 per week or placebo for 12 months was designed. A total of 472 subjects, 236 in each of the intervention groups, were included in the analyses. MAIN OUTCOME MEASURES: Baseline serum concentrations and increases in serum total 25(OH)D, directly measured free 25(OH)D, calculated free 25(OH)D and DBP. RESULTS: Serum total 25(OH)D and DBP concentrations were significantly lower in subjects with the phenotype Gc2/Gc2 compared to phenotypes with the Gc1S allele, and lower in males compared to females. When using directly measured free 25(OH)D, the differences related to DBP phenotypes and sexes were clearly diminished. All calculated free 25(OH)D concentrations were overestimated compared to the directly measured free 25(OH)D. Serum parathyroid hormone showed an inverse correlation with all vitamin D parameters analyzed. The increases after 12 months of vitamin D supplementation were not significantly different for any of the vitamin D parameters regardless of DBP phenotype, sex or age. Supplementation with vitamin D did not affect serum DBP. CONCLUSION: Direct measurements of free 25(OH)D reduce the differences seen in total 25(OH)D between DBP phenotype groups and sexes, probably caused by differences in DBP concentrations. With conditions affecting serum DBP concentrations, direct measurements of free 25(OH)D should be considered.

No effect of high-dose vitamin D supplementation on glycemic status or cardiovascular risk factors in subjects with prediabetes.

OBJECTIVE: In observational studies, low serum 25-hydroxyvitamin D [25(OH)D] concentrations have been associated with insulin resistance and other risk factors for cardiovascular disease. RESEARCH DESIGN AND METHODS: We present 1-year data from an ongoing 5-year trial in 511 individuals with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) randomly assigned to 20,000 IU/week vitamin D3 or placebo. An oral glucose tolerance test was performed at baseline and after 1 year. RESULTS: Mean baseline serum 25(OH)D was 59.9 nmol/L and 61.1 nmol/L in the vitamin D and placebo groups, respectively, and increased by 45.8 nmol/L and 3.4 nmol/L, respectively. With adjustment for baseline concentrations, no differences in measures of glucose metabolism, insulin secretion or sensitivity, blood pressure, or hs-CRP were found after 1 year. There was a slight, but significant decrease in total and LDL cholesterol in the vitamin D group compared with the placebo group, but as there was also a decrease in HDL cholesterol, the change in the total/HDL cholesterol ratio did not differ significantly. Only analyzing subjects with 25(OH)D <50 nmol/L did not change the results. CONCLUSIONS: This study shows that vitamin D supplementation does not improve glycemic indices, blood pressure, or lipid status in subjects with IFG and/or IGT.