(RxWiki News) Low levels of vitamin D have been linked to cancer, heart disease and other serious illnesses. But is a lack of vitamin D a cause or result of disease?
A recent review of previous studies and trials examined the relationship between vitamin D and illness.
The researchers found that low vitamin D levels tended to accompany poor health and disease progression. However, clinical trials testing vitamin D supplementation did not result in significantly improved health.
The authors of this review concluded that low levels of vitamin D seem to be an effect of illness, not a cause.
"Talk to your doctor about any supplements you are taking."
Philippe Autier, MD, MPH, a professor at the International Prevention Research Institute, led this review on vitamin D and its effects on health.
Vitamin D helps the body absorb calcium and phosphate. According to Dr. Autier and colleagues, low vitamin D levels have been associated with cancer, heart disease and death. However, research has not established whether low vitamin D levels are the cause or result of these health conditions.
This review included 290 prospective studies and 172 randomized trials on vitamin D levels and major health outcomes.
A total of 11 studies addressed the link between vitamin D levels in patients who were diagnosed with cancer, as well as tumor characteristics or patient survival rates.
Some of the studies showed that patients with melanoma and breast, colorectal and prostate cancer were more likely to survive if they had higher vitamin D levels at diagnosis. The researchers found no significant link between vitamin D and lung, head or neck cancer.
Other studies showed moderate to strong decreases in heart disease, inflammation, glucose metabolism disorders (e.g., diabetes) and weight gain in participants who had higher levels of vitamin D.
However, studies that used vitamin D interventions generally did not lead to positive health results.
Seven trials measured the effects of vitamin D supplements on blood vessel function. Supplementation only resulted in favorable results for three of 15 outcomes.
For 31 trials assessing the effects of vitamin D on blood sugar and metabolic health problems like diabetes, only four of 91 outcomes improved after supplementation.
The results of multiple sclerosis trials also did not point to any relationship between vitamin D levels and disease course.
The researchers found that vitamin D levels were sometimes linked to favorable health conditions, but vitamin D supplementation did not usually provide a significant benefit. Given this relationship, they suggested that low vitamin D levels are a result, not a cause, of poor health.
The authors of this review did note that some trials found that vitamin D supplementation led to a reduction in death. However, they noted that the supplementation primarily affected elderly women.
These researchers also suggested that low vitamin D levels may be the result of the inflammation that commonly accompanies illness.
This study was published in The Lancet Diabetes and Endocrinology on December 5.
The authors did not declare conflicts of interest or funding sources.