People who do not get enough vitamin D have a higher chance of getting bladder cancer, a new study has suggested.
Experts said the findings stress the importance of getting the right levels of the vitamin.
During the summer months most people get sufficient vitamin D from sunlight but in winter it can be difficult to maintain the levels needed, despite it being present in foods such as oily fish, red meat, egg yolks and some fortified foods.
Five out of seven previous studies showed low vitamin D levels were associated with bladder cancer risk.
The researchers, from the University of Warwick and University Hospital Coventry and Warwickshire, also looked at bladder cells and concluded that certain cells, known as epithelial cells, are able to activate and respond to vitamin D, which in turn can stimulate an immune response.
Dr Rosemary Bland, lead author of the study, said:
It has been estimated that as many as one in five UK adults are vitamin D deficient, and three in five have low levels.
In July, Public Health England said that people should consider taking supplements in the winter to ensure they are getting enough vitamin D.
Across the UK there were more than 10,000 new cases of bladder cancer diagnosed in 2013 more than 5,300 people died from the disease in 2014, according to Cancer Research UK figures.