Vitamin D is made by the skin when exposed to sunlight. It maintains calcium levels in the body to keep bones, teeth and muscles healthy. Researchers analysed data from the Japan Public Health Center-based Prospective (JPHC) Study, involving male and female participants aged between 40 to 69 years. Participants provided detailed information on their medical history, diet and lifestyle, and blood samples were taken to measure vitamin D levels.

Vitamin D levels varied depending on the time of year the sample was taken, tending to be higher during the summer and autumn than in the winter or spring. After accounting for this seasonal variation, samples were split into four groups, ranging from the lowest to highest levels of vitamin D. Participants were then monitored for an average of 16 years, during which time 3,301 new cases of cancer were recorded.

After considering cancer risk factors like age, weight, activity levels, smoking, alcohol intake and dietary factors, the researchers found that a higher level of vitamin D was associated with a lower risk of overall cancer in both men and women. Higher vitamin D levels were also associated with a lower risk of liver cancer, and the association was more evident in men than in women.

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