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A new study looks at the relationship between sun exposure, age, and colon cancer. Karen Cornelius/EyeEm/Getty Images
  • Researchers recently investigated links between colon cancer risk and exposure to lower levels of ultraviolet B (UVB) radiation from sunlight.
  • The scientists focused on this relationship in different age groups.
  • The results suggest that the risk of colon cancer is significantly higher for individuals over 45 years who have less exposure to UVB radiation.
  • The researchers say their findings support the need for public health programs to prevent vitamin D deficiency at national and global levels.

Colorectal cancer, which is also called colon cancer, occurs in the large intestine or rectum. The condition usually begins with abnormal growths called polyps.

According to the World Health Organization (WHO), colorectal cancer is the third most common cancer with over 1.93 million new cases worldwide in 2020. It is also the second most common cause of cancer deaths worldwide and was responsible for 935,000 deaths in 2020.

Risk factors for colorectal cancer include obesity, a sedentary lifestyle, and diets that are high in fat and red meat. Studies have also shown that low vitamin D levels are a potential risk factor for colorectal cancer and that chronic vitamin D deficiency produces molecular changes that increase cancer risk.

According to an older study, exposure to UVB radiation from sunlight supplies men with no underlying health conditions around 80% of their vitamin D needs. In 2013, researchers found a link between UVB exposure and incidence of colorectal cancer. However, the study did not investigate how UVB exposure affects colorectal cancer risk among different age groups.

Understanding how exposure to UVB radiation affects the risk of colorectal cancer in different age groups could help researchers understand the long-term effects of vitamin D deficiency, screen for at-risk individuals, and develop preventive healthcare strategies.

Scientists from the University of California, San Diego, recently conducted a study investigating the link between age, exposure to UVB radiation from sunlight, and incidence of colorectal cancer.

Their findings suggest that less UVB exposure increases the risk of developing colorectal cancer in older age groups than younger ones. After controlling for various factors, they found the relationship to be particularly significant for people 45 years and above.

“Differences in UVB light accounted for a large amount of the variation we saw in colorectal cancer rates, especially for people over age 45,” explained Raphael Cuomo, co-author of the study, “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 study appears in BMC Public Health.

The scientists used data from the Global Cancer (GLOBOCAN) database via a data visualization tool developed by the International Agency for Research on Cancer (IARC). The data provided age-stratified incidence rates of colorectal cancer in 186 countries in 2018.

The scientists also used data collected in April 2017 from the National Aeronautics and Space Association (NASA) Earth Observing System Aura spacecraft, alongside stratospheric ozone data from NASA, to account for UVB radiation in light of cloud cover and aerosols in different countries.

To make their analysis more comprehensive, they accounted for additional factors. These included skin pigmentation, smoking prevalence, life expectancy, GDP per capita, urbanization, and animal consumption. They also factored in measurements of vitamin D taken from blood tests in the different countries.

In their analysis, they split incidence rates of colorectal cancer into different age groups: 0–14, 15–29, 30–44, 45–59, 60–74, and 75 years and above.

After controlling for all the above factors, the researchers found that the risk of colorectal cancer was higher in those over 45 years who had lower exposure to UVB radiation.

To explain their results, the researchers say that vitamin D plays a protective role at different stages of cancer by regulating cadherins, which are a group of proteins that protect the space in between cells from harmful agents that could lead to cancer progression.

Short bursts of vitamin D deficiency may have little impact on the body’s regulation of cadherins. However, when the effects of vitamin D deficiency compound over time, they may increase the risk of colorectal cancer.

According to the researchers, this may explain why rates of colorectal cancer increase faster after 45 years under low exposure to UVB radiation, as the consequences of vitamin D deficiency have longer to accumulate.

The researchers conclude that their findings support the need for public health programs to avoid vitamin D deficiency at national and global levels. Future research, they say, could aim to identify different cancer types that improve with vitamin D supplementation.

They note, however, that UVB is not a perfect proxy of vitamin D levels and that their study failed to account for important factors that could have influenced their results, including vitamin D supplementation, clothing cover, and altitude.

Moreover, they note that there were inherent limitations in their estimates of colorectal rates for some countries. The researchers said that they sometimes used a neighboring country’s colorectal cancer estimates where data for a country was unavailable.

Medical News Today spoke with Marji McCullough, SCD, RD, Senior Scientific Director of Epidemiology Research at the American Cancer Society. She noted that the authors could not take into account levels of body fat and physical activity.

However, overall, McCullough concludes:

“Regardless of potential associations of vitamin D deficiency and colorectal cancer and other health outcomes, it is important to maintain adequate blood levels of vitamin D for bone health.” She also reminds us that “excessive UVB radiation is a major risk factor for skin cancer. There are other ways to get vitamin D, including diet and supplements.”