Vitamin D levels have been linked to an increased risk of bladder cancer - but the source is a systematic review of just seven studies, so no one outside mainstream media and supplement salespeople promote panic about it.

Vitamin D, which is produced by the body through exposure to sunshine, helps the body control calcium and phosphate levels. Vitamin D can also be obtained from food sources such as fatty fish and egg yolks but it can be difficult to obtain enough vitamin D from food alone in countries with little sunlight so food is often fortified. Vitamin D has become a gigantic supplement fad and to capitalize on that some studies have linked vitamin D deficiency with a host of health problems including cardiovascular disease, cognitive impairment, autoimmune conditions, and cancer.

In this work, researchers from the University of Warwick and University Hospital Coventry and Warwickshire, Coventry and the investigated the link between vitamin D and bladder cancer risk. They reviewed seven studies on the topic which ranged from having 112 to 1125 participants each. Five out of the seven studies linked low vitamin D levels to an increased risk of bladder cancer.

In a separate experiment, the researchers then looked at the cells that line the bladder, known as transitional epithelial cells, and found that these cells are able to activate and respond to vitamin D, which in turn can stimulate an immune response. According to lead author of the study Dr Rosemary Bland, this is important because the immune system may have a role in cancer prevention by identifying abnormal cells before they develop into cancer.

"More clinical studies are required to test this association, but our work suggests that low levels of vitamin D in the blood may prevent the cells within the bladder from stimulating an adequate response to abnormal cells," said Dr Bland. "As vitamin D is cheap and safe, its potential use in cancer prevention is exciting and could potentially impact on the lives of many people."

Presented at the Society for Endocrinology annual conference in Brighton.