Experts call for clinical trials to test non-skeletal benefits of vitamin D
The Endocrine Society's new scientific statement published online today represents the first comprehensive evaluation of both the basic and clinical evidence related to the non-skeletal effects of vitamin D. The statement addresses current research regarding the associations of vitamin D with immune function, hypertension, stroke, skin conditions and maternal/fetal health.
Vitamin D is a steroid hormone that regulates calcium and phosphate levels in the bloodstream and promotes healthy bone growth. Vitamin D deficiency is common throughout the world and results in abnormalities of calcium, phosphorus and bone metabolism which can lead to muscle weakness, osteomalacia, osteopenia and osteoporosis. While some observational studies have shown that benefits of vitamin D may extend beyond bone health, research findings remain inconsistent.
"The role of vitamin D supplementation in the prevention and treatment of chronic non-skeletal diseases remains to be determined," says Clifford Rosen, MD, of Tufts University School of Medicine and chair of the task force that authored the statement. "We need large randomized controlled trials and dose-response data to test the effects of vitamin D on chronic disease outcomes including autoimmunity, obesity, diabetes, hypertension and heart disease."
The scientific statement outlines the evidence that defines the effects of vitamin D on epidermal, neuromuscular, maternal/fetal and neoplastic (abnormal growth) tissues. The authors critically evaluated the literature for each organ system utilizing available evidence from observational studies and randomized trials to determine the strength of associations between vitamin D and tissue-specific outcomes.
Conclusions from the statement include:
- Topical and oral vitamin D may be useful in treating skin disorders such as psoriasis, though large-scale randomized placebo-controlled clinical trials are needed to demonstrate the efficacy of treatment with vitamin D on skin disorders or the prevention of skin cancer.
- The ever-expanding obesity epidemic has been associated with a rising prevalence of vitamin D deficiency, but a cause-and-effect relationship has not been established. Strong evidence does not exist to support the tenet that vitamin D supplementation reduces the risk of type 2 diabetes or the metabolic syndrome.
- Vitamin D supplementation is likely to reduce the risk of falls, particularly in individuals who have low baseline levels (<20 ng/ml) and are supplemented with calcium as well.
- Recent systematic reviews have found that evidence that vitamin D reduces cancer incidence are inconclusive as to causality. Observational evidence is strongest for colorectal cancer but is weak or inconsistent for breast, prostate and total cancer.
- There is a possibility that vitamin D supplementation may lower cardiovascular disease risk, but there are limitations in applying observational data to clinical practice. An insufficiency of evidence from clinical trials does not support recommending vitamin D supplementation for lowering cardiovascular disease risk at this time.
- Clinical trials are needed to test whether vitamin D supplementation during pregnancy will prevent type 1 diabetes in offspring.