Inadequate exposure to UVB light from the sun may be associated with an increased risk of colorectal cancer, particularly in older age groups, according to a study using data on 186 countries, published in BMC Public Health.
Researchers at the University of California San Diego, USA investigated possible associations between global levels of UVB light in 2017 and rates of colorectal cancer for different countries and age groups in 2018.
The authors found that lower UVB exposure was significantly correlated with higher rates of colorectal cancer across all age groups from 0 to over 75 years in people living in the 186 countries included in the study. The association between lower UVB and risk of colorectal cancer remained significant for those aged above 45 after other factors, such as skin pigmentation, life expectancy and smoking were taken into consideration. Data on these factors were available for 148 countries.
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. Future research could look directly at the potential benefits on colorectal cancer of correcting vitamin D deficiencies, especially in older age groups, according to the authors.
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 (a naturally-occurring gas that filters the sun's radiation) 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 caution 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 caution 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.
Study details
Could age increase the strength of inverse association between ultraviolet B exposure and colorectal cancer?
Vidya Lakshmi Purushothaman, Raphael E. Cuomo, Cedric F. Garland &Timothy K. Mackey
Published in BMC 25 July 2021
Abstract
Background
Vitamin D has been identified as a potential protective factor in the development of colorectal cancer (CRC). We expect to see a stronger association of ultraviolet B (UVB) exposure and CRC crude rates with increasing age since chronic vitamin D deficiency leads to sustained molecular changes that increase cancer risk. The DINOMIT (disjunction, initiation, natural selection, overgrowth, metastasis, involution, and transition) model postulates various stages of cancer development due to vitamin D deficiency and the associated latency period. The purpose of this study is to examine this age-dependent inverse relationship globally.
Methods
In this ecological study, a series of linear and polynomial regression tests were performed between country-specific UVB estimates adjusted for cloud cover and crude incidence rates of CRC for different age groups. Multiple linear regression was used to investigate the association between crude incidence rates of colorectal cancer and UVB estimate adjusting for urbanisation, skin pigmentation, smoking, animal consumption, per capita GDP, and life expectancy. Statistical analysis was followed by geospatial visualisation by producing choropleth maps.
Results
The inverse relationship between UVB exposure and CRC crude rates was stronger in older age groups at the country level. Quadratic curve fitting was preferred, and these models were statistically significant for all age groups. The inverse association between crude incidence rates of CRC and UVB exposure was statistically significant for age groups above 45 years, after controlling for covariates.
Conclusion
The age-dependent inverse association between UVB exposure and incidence of colorectal cancer exhibits a greater effect size among older age groups in global analyses. Studying the effect of chronic vitamin D deficiency on colorectal cancer etiology will help in understanding the necessity for population-wide screening programs for vitamin D deficiency, especially in regions with inadequate UVB exposure. Further studies are required to assess the need for adequate public health programs such as selective supplementation and food fortification.
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