Taking vitamin D supplements for bone health is fine but using it to prevent and treat other diseases doesn't have clear evidence, a panel of medical experts says.
The Endocrine Society, which includes American and Canadian specialists, reviewed the evidence on vitamin D beyond bone health.
Vitamin D is a steroid hormone that regulates calcium and phosphate levels in the blood and promotes the growth of healthy bones.
"The role of vitamin D supplementation in the prevention and treatment of chronic non-skeletal diseases remains to be determined," Dr. Clifford Rosen of Tufts University School of Medicine and chair of the task force said in a statement Friday.
"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."
Vitamin D deficiency can lead to muscle weakness, osteoporosis and bone softening.
Canadian prevention trial
Before releasing their scientific statement on vitamin D, the society's panel evaluated the literature for each organ system using information from randomized trial experiments and observational studies.
Their conclusions included:
- Vitamin D pills, gels or ointments may be useful in treating skin disorders such as psoriasis but large, placebo-controlled clinical trials are needed to test if it works to prevent or treat skin cancer.
- There's no strong evidence that vitamin D supplementation reduces the risk of Type 2 diabetes or metabolic syndrome, a group of risk factors like high blood pressure, high blood sugar, excess abdominal fat, abnormal cholesterol levels and obesity that occur together.
- The supplements are likely to reduce the risk of falls, especially in those who have low levels and are also taking calcium pills.
- Observational evidence is strongest for vitamin D reducing colorectal cancer but the proof is weak or inconsistent for cancer overall and breast and prostate tumours.
- There's not enough evidence from clinical trials to support taking vitamin D to lower cardiovascular disease risk.
Clinical trials are also needed to test whether giving vitamin D supplements in pregnancy will prevent Type 1 diabetes after birth. Dr. Shayne Taback, a pediatric endocrinologist in Winnipeg, is scheduled to find out next month whether a Canadian clinical trial will be funded.
Research investigating vitamin D was aided by the discovery of its receptor in 1987.
"Its subsequent identification in virtually all tissues spurred further basic and clinical studies and led to a much greater appreciation of the physiological role of vitamin D," the group wrote.
"At the same time, interest in vitamin D as a therapeutic modality for the prevention of chronic diseases grew exponentially. Indeed, in a two-month span during the summer of 2011, there were more than 500 publications centered on vitamin D, most of which [involved] its relationship to nonskeletal tissues."
In 2010, the Institute of Medicine, an independent organization that advises the U.S. and Canadian governments, concluded most people are getting enough of the vitamin.
The new statement was published in Endocrine Reviews.