The findings add to a body of evidence suggesting that low vitamin D is detrimental to health.

Some vitamin D comes from the diet. Good sources include fatty fish and fish oil, dairy products, mushrooms, liver, and egg yolks. However, it is mostly synthesized when the body is exposed to sunlight. Dietary sources alone cannot normally provide sufficient vitamin D.

Vitamin D helps the body to maintain healthy levels of calcium and phosphates. Low levels have been linked to a range of health problems.

In children, it can lead to bone deformities, such as rickets. Concentrations tend to decrease with age, and, in time, a lack of vitamin D can lead to osteoporosis, especially in postmenopausal women.

Low levels have also been linked to cognitive impairment, cardiovascular disease, cancer, and autoimmune conditions.
Who is at risk of vitamin D deficiency?

Vitamin D deficiency is common among people with limited exposure to sunlight. This includes populations from northern regions, where winter days are short, and those in climates where it is too hot to spend time outdoors.

Fast facts about bladder cancer

    76,960 new cases of bladder cancer are expected in the U.S. in 2016
    There are expected to be 16,390 deaths from bladder cancer in 2016
    77.5 percent of patients survive for 5 years or more.

Others at risk include those who cover up or use sunscreen with a strong SPF factor to avoid sunburn or skin cancer, those who cover their bodies for cultural or religious reasons, and those who stay out of the sun to keep their skin pale. People with darker skin are also more prone to low vitamin D levels.

Overconsumption of sugary drinks may have an impact on levels of vitamin D.

In the United States, the Centers for Disease Control and Prevention (CDC) note that between 2002-2006, 8 percent of the population aged 1 year or over were at risk of vitamin D deficiency, 24 percent were at risk of inadequacy, and in only 17 percent met desirable levels.

Fewer than 1 percent raised concerns about an excess of vitamin D.

Around 2.4 percent of men and women in the U.S. are expected to develop bladder cancer.

It accounts for 4.6 percent of all new cancer cases and is responsible for 2.8 percent of cancer deaths.

Researchers from the University of Warwick and Coventry in the U.K., led by Dr. Rosemary Bland, wanted to know more about how synthesis of vitamin D might affect immune responses in specific tissues.
Vitamin D may benefit immune response

They carried out a systematic review of seven studies to investigate the link between vitamin D and bladder cancer. The number of participants per study ranged from 112 to 1,125. Some of the studies measured vitamin D levels before diagnosis, some during, and some at the follow-up stage.

Five out of the seven studies found that the risk of bladder cancer goes up when vitamin D levels are low. Higher vitamin D levels also correlated with better survival and outcomes in people with bladder cancer.

The team also examined the cells that line the bladder, known as transitional epithelial cells. They found that these cells can activate and respond to vitamin D, and that they can synthesize enough vitamin D to trigger a local immune response. By recognizing abnormal cells before they develop further, the immune system may be able to use this information to prevent cancer.

The researchers conclude that "bladder cancer risk correlates with low serum [vitamin D] levels." Dr. Bland suggests that if this is confirmed, administering supplementary vitamin D could be a safe and economical means of prevention.

    "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. 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."

    Dr. Rosemary Bland

Dr. Bland told Medical News Today that vitamin D has been associated with an increased risk of other cancers, too. She added that she would suggest a supplement for people with low vitamin D.

The authors call for clinical studies to confirm the findings.