High levels of vitamin D may be linked to a lower risk of developing cancer, including liver cancer, concludes a large study of Japanese adults, published March 7, 2018 in the journal BMJ.
This study is one of the first to look at the effects of vitamin D and cancer risk in an Asian population. Researchers say their findings support the theory that vitamin D may help protect against certain cancers.
Vitamin D is produced by the skin in response to sunlight through the action of ultraviolet (UV) rays. It helps maintain calcium levels in the body to keep bones, teeth and muscles healthy.
While the benefits of vitamin D are well known on bone diseases (it plays a vital role in bone mineralization), there is growing evidence that vitamin D can benefit other chronic diseases, including including some cancers.
But so far, most studies have been conducted in European and American populations, and data from Asian populations are limited.
THE METABOLISM OF VITAMIN D VARIES BY ETHNICITY
Since vitamin D concentrations and metabolism may vary by ethnicity, it is important to know if similar effects would be observed in non-Caucasian populations.
For example, an international research team based in Japan investigated whether vitamin D was associated with cancer risk. They analyzed data from the Prospective Study (JPHC) of the Japan Public Health Center, which involved 33,736 male and female participants aged 40-69 .
At the beginning of the study, 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 according to the time of year in which the sample was taken, and tended to be higher during the summer and fall months than in winter or spring . After taking into account this seasonal variation, the samples were divided into four groups, ranging from the lowest to the highest levels of vitamin D. The participants were then followed for an average of 16 years, during which 3,301 new cases of cancer were recorded.
RESULTS THAT SUPPORT THE THEORY THAT VITAMIN D CAN PROTECT AGAINST THE RISK OF CANCER
After adjusting for several known cancer risk factors, such as age, weight, physical activity , smoking, alcohol consumption and dietary factors, the researchers found that a higher rate of vitamin D decreased the relative risk of cancer (all cancers combined) for men and women.
Higher levels of vitamin D were also associated with a lower relative risk of liver cancer, up to -30 to -50%, and the association was more evident in men than in women.
No association was found for lung cancer or prostate cancer, and the authors note that none of the cancers examined showed an increased risk associated with higher levels of vitamin D. results were unchanged after taking additional dietary factors into account and after further analysis to test the strength of the results.
Finally, the researchers highlight some of the limitations of the study. For example, the number of organ-specific cancers was relatively low. And although they have adjusted several known risk factors, they can not rule out the possibility that other unmeasured factors may have influenced the results, making it difficult to come to a firm conclusion about cause and effect.
Nevertheless, the main strengths of this study include the large sample size for all types of cancers, a long follow-up period and the large number of blood samples analyzed.
To conclude, the authors say that their results support the theory that vitamin D can protect against the risk of cancer, but that there could be a ceiling effect, which could suggest that there is no risk of cancer. additional benefits beyond a certain level of vitamin D.