Vitamin D: Researchers continue to explore wide range of benefits

Of all the vitamins, it is perhaps vitamin D that garners the most attention and claims about its ability to prevent or improve a wide range of chronic conditions. Indeed, vitamin D has been touted to benefit everything from autoimmunity and bone mineral disease to several cancers, diabetes, cardiovascular disease, and multiple sclerosis.

Here are some of the latest findings on the effects of vitamin D, which were chosen from literally hundreds of studies published this year alone:

• May lower oxidative stress parameters. In a systematic review and meta-analysis of 13 clinical trials, researchers found that vitamin D supplementation increased serum levels of total antioxidant capacity (P=0.001) and glutathione (an important antioxidant; P=0.003), and decreased malondialdehyde (a marker for oxidative stress) concentrations (P < 0.001).
• May improve left ventricular function in patients with heart failure (HF) aged ≥ 50 years. Researchers conducted a post hoc analysis of the Effect of Vitamin D on Mortality in Heart Failure (EVITA) study to determine the effects of 3 years of daily vitamin D supplementation (4,000 IU/d) on echocardiography parameters in 400 patients with HF. They found no effects at 12 or 36 months in any left ventricular echocardiographic parameters. They did find, however, that vitamin D supplementation was associated with a 2.73% increase in left ventricular ejection fraction at 12 months in patients aged ≥ 50 years, which was still significant at 36 months (2.60%).

• May improve symptoms of autism spectrum disorder (ASD) in children. In a placebo-controlled trial, researchers assessed the effects of vitamin D (2,000 IU/d), docosahexaenoic acid (722 mg/d), or a combination of both in 73 children aged 2.5 to 8 years with ASD. They found significant improvements in scores of social awareness with both docosahexaenoic acid alone and combined with vitamin D (P=0.03). They also observed a trend towards greater improvements with the combination of these two supplements in measures of social communicative functions and taste and smell.
• May protect against acute respiratory infections. In a meta-analysis, researchers evaluated 25 randomized controlled trials of vitamin D3 or vitamin D2 supplementation that assessed the incidence of acute respiratory infection as an outcome of efficacy. They found that vitamin D supplementation significantly reduced the risk of acute respiratory infections in all 10,933 subjects included in the final analysis (adjusted OR: 0.88; 95% CI: 0.81-0.96; heterogeneity P < 0.001). Further, they found that the protective effects of vitamin D were more pronounced in those with a lower baseline concentration of 25-hydroxyvitamin D (25[OH]D; < 25 nmol/L) than in those with a higher concentration (≥ 25 nmol/L; adjusted OR: 0.30 vs 0.75; P=0.006).

• May improve health-related quality of life (HRQOL) in patients with breast cancer in early survivorship. In 553 breast cancer patients/survivors enrolled in a matched cohort study of breast cancer outcomes, researchers found that over 50% used vitamin D supplements, and that those who used a naturopathic oncology provider in early survivorship were more likely to use them (P < 0.05). Baseline use of vitamin D supplements was associated with higher levels of self-reported HRQOL at enrollment (P < 0.05) and predictive of better HRQOL at 6-month follow-up (P < 0.05). Researchers also found that sufficient serum levels of vitamin D at baseline and follow-up were associated with better HRQOL at follow-up (P < 0.05).
• Higher serum vitamin D levels may be associated with lower blood glucose levels. In a cross-sectional study, researchers included 680 women aged 35-74 years, in whom they measured serum 25[OH]D and glucose levels via fasting blood samples. Serum vitamin D levels less than 30 ng/mL (65.4% of subjects) were associated with blood glucose levels of 100 mg/dL or more (OR: 1.29; 95% CI: 1.05-1.57), as were levels of less than 20 ng/mL (OR: 1.25; 95% CI: 1.04-1.50).

In all of these studies, researchers stressed the need for further investigation and clinical trials to validate their results.