We know that excessive exposure to radiation UVB from the sun promotes skin cancer. But, conversely, not exposing yourself to it enough can be associated with an increased risk of colorectal cancer, especially in people over 45 years of age. In any case, this is revealed by a study using data from 186 countries and published in the journal BMC Public Health.
A link between UVB rays and the risk of colorectal cancer
Researchers at the University of California, San Diego, USA, investigated possible associations between levels of UVB radiation and the colorectal cancer rates the following year, in different countries and for different age groups. For this, they used UVB estimates obtained by NASA’s EOS Aura spacecraft, in April 2017, and data on the proportion of colorectal cancers in 2018 for 186 countries from the Global Cancer database.
They discovered that lower exposure to this light was significantly correlated with colorectal cancer rates. higher, in all age groups. They then took into account other factors, such as skin pigmentation, life expectancy and smoking. After the introduction of these variables, the association between UVB decline and colorectal cancer risk remained significant for people of over 45 years old.
Lack of vitamin D could be to blame
According to the study authors, these results could be explained by the fact that lower exposure to ultraviolet rays can reduce the levels of vitamin D. However, previous work has already shown that a vitamin deficiency is associated with an increased risk of colorectal cancer.
“Although this is still preliminary evidence, it is possible that older people, in particular, may reduce their risk of colorectal cancer by correcting their deficiency in vitamin D”, suggests Professor Raphael Cuomo, co-author of the study.
Sun exposure: 15 to 30 minutes, twice a week
“Sun exposure is beneficial provided that it remains reasonable”, also recalls Dr. Annie Sasco, epidemiologist, on the site of the Cancer League. “Twice a week, 15 to 30 minutes enough to properly metabolize vitamin D”, specifies the expert.
Scientists warn, however, that other factors can influence UVB exposure and vitamin D levels, such as the intake of food supplements, the clothes worn or even air pollution, which were not included in the study. They also state that the nature observational of the latter does not allow, for the moment, to establish a link of cause and effect between insufficient exposure to UVB and colorectal cancer. Further work is needed to confirm this relationship.
