The cancer risk for people who have a sufficient vitamin D intake is about 20 percent lower than that for people who lack the vitamin, a study by researchers at Japan's National Cancer Center indicates.
The finding, published in the online version of the British medical journal BMJ on March 8, came from what was said to be the largest study examining the relationship between vitamin D and cancer.
The team followed a group of men and women across Japan for an average of 16 years until 2009 using blood samples they had provided. The subjects were aged between 40 and 69. For approximately 8,000 subjects, researchers examined the relationship between the concentration of vitamin D in their blood and the occurrence of cancer.
Researchers separated the subjects into four groups according to their vitamin D levels. Taking the group with the lowest concentration of the vitamin as a base, researchers found that the cancer risk for those in the second-lowest quartile was 19 percent lower than those in the bottom group. For the group with the second-highest concentration, the risk fell 25 percent, while for those with the highest concentration the risk of developing cancer was 22 percent lower.
By type, liver cancer saw the biggest drop. Because liver cancer progresses from hepatitis, there is said to be a possibility that the property of vitamin D of restraining inflammation lowers the risk.
Vitamin D is found in abundance in seafood and mushrooms, and can also be produced in the body when one is exposed to sunlight.
Taiki Yamaji, section head at the National Cancer Center Division of Epidemiology, who was involved in the study, commented, "To ingest vitamin D, it is important to have a balanced diet and get an appropriate amount of sunlight. However, it's not a case of 'the higher the better' when it comes to the concentration of vitamin D in the blood, so there's no need for people to ingest it excessively through supplements and the like."