A lack of exposure to UVB light from the sun may increase an individual’s risk of developing colorectal cancer, a new global study has found.
Researchers from the University of California San Diego, USA, analysed data from 186 countries to investigate the potential links between levels of UVB light in 2017 and rates of colorectal cancer for different countries and age groups in 2018. They discovered a strong association between low exposure to UVB light and higher rates of colorectal cancer across all age groups and countries surveyed.
The findings have been published in the open access journal BMC Public Health.
The researchers looked at data from people aged 0 to over 75 years old living in 186 different countries. The association between lower UVB and risk of colorectal cancer remained significant for those aged over 45 years old after other factors – such as skin pigmentation, life expectancy, and smoking – were taken into consideration. Data on these factors were available for 148 countries.
Vitamin D levels
The authors suggest that lower UVB exposure may reduce levels of vitamin D. Vitamin D deficiency has previously been associated with an increased risk of colorectal cancer.
The researchers recommend that future studies should look directly at the potential benefits on colorectal cancer of correcting vitamin D deficiencies.
Raphael Cuomo, Co-author of the study, said: “Differences in UVB light accounted for a large amount of the variation we saw in colorectal cancer rates, especially for people over age 45. Although this is still preliminary evidence, it may be that older individuals, in particular, may reduce their risk of colorectal cancer by correcting deficiencies in vitamin D.”
The authors used UVB estimates obtained by the NASA EOS Aura spacecraft in April 2017 and data on colorectal cancer rates in 2018 for 186 countries from the Global Cancer (GLOBOCAN) database. They also collected data for 148 countries on skin pigmentation, life expectancy, smoking, stratospheric ozone and other factors which may influence health and UVB exposure from previous literature and databases. Countries with lower UVB included Norway, Denmark, and Canada, while countries with higher UVB included United Arab Emirates, Sudan, Nigeria, and India.
The authors do acknowledge that other factors may affect UVB exposure and vitamin D levels, such as vitamin D supplements, clothing, and air pollution, which were not included in the study. They also warn that the observational nature of the study does not allow for conclusions about cause and effect and more work is needed to understand the relationship between UVB and vitamin D with colorectal cancer in more detail.