Scientists Link Low Sun Exposure to Leukemia

Epidemiologists at UCSD School of Medicine reported that people living at higher altitudes with lower sunlight and ultraviolet B exposure are at least twice as likely to develop leukemia than equatorial populations. UCSD co-authors Cedric Garland, Raphael Cuomo, Edward Gorham and Sharif Mohr published their findings associating vitamin D levels with leukemia in an online issue of PLOS One last month.

The study analyzed age and elevation-adjusted incidence rates of leukemia using data collected in 172 countries by the International Agency for Research on Cancer of the World Health Organization for its GLOBOCAN Project. This information was compared with cloud-cover data from the International Satellite Cloud Climatology Project.

Doctor of Public Health and Professor in UCSD’s department of family medicine and public health Cedric Garland explained that populations farther away from the equators will, on average, be exposed to solar energy that has traveled farther through the Earth’s atmosphere, thereby lowering the amount of UVB available to the skin.

“The results suggest that much of the burden of leukemia worldwide is due to the epidemic of vitamin D deficiency we are experiencing in winter in populations distant from the equator,” Garland told UCSD Health. “People who live in areas with low solar UVB exposure tend to have low levels of vitamin D metabolites in their blood … [placing] them at high risk of certain cancers, including leukemia.”

Revelle College junior and Community Service Coordinator of the Public Health Club Kristina Chepak emphasized the necessity of publicizing this information order to minimize individual risks of developing leukemia. 

“The actions needed to be taken in public health would be to educate the population who are not exposed to enough sunlight on different ways to obtain vitamin D, like taking vitamin D supplements or obtaining it from fish, eggs or milk and orange juice that are fortified with vitamin D,” Chepak told the UCSD Guardian.

According to the study, a molecule found in the skin absorbs the wavelengths from sunlight, and the liver and kidneys metabolize it. This molecule then acts on vitamin D receptors in bone marrow to make up junctions that help tightly bind cells together, causing increased contact inhibition of cancer. The process results in transcription of G1-phase inhibitors, which control mitosis and may therefore help prevent the uncontrolled proliferation of white blood cells that is characteristic of leukemia.

The researchers’ conclusion is consistent with results from similar investigations concerning other forms of cancers including breast, colon, pancreatic, bladder and multiple myeloma. In each study, reduced UVB radiation exposure and lower vitamin D levels were associated with higher risks of cancer. Leukemia rates were highest in countries relatively closer to the poles, such as the United States, Australia, New Zealand, Chile, Ireland and Canada; they were lowest in countries closer to the equator, including Bolivia, Samoa, Madagascar and Nigeria.

“These studies do not necessarily provide final evidence, but they have been helpful in the past in identifying associations that have helped minimize cancer risk,” Garland explained.

According to the American Cancer Society, 54,270 cases and 24,450 deaths from leukemia occur in the United States alone each year, and there is no known way to completely prevent most types of leukemia. Revelle junior and External Affairs Coordinator for PHC Omar Sajjad expressed that while adequate amounts of vitamin D may be a preventative measure, the need for sun protection still exists.

“The key thing is to know how to limit your risk for sun-related cancers,” Sajjad told the Guardian. “Try to avoid the sun during the times of day when its rays are strongest.”

Chepak suggested that people aim for 20 to 30 minutes of sun exposure while wearing protective sunscreen. She also encourages an increased consumption of fish and eggs along with products that are fortified with vitamin D, including orange juice and milk. Lastly, Chepak acknowledged that substitutes for sunlight, including safe tanning beds and portable full-spectrum light panels, could provide healthy amounts of UVB.

“Sweden created a form of light therapy that is used to help with Seasonal Affective Disorder, or ‘winter blues,’ caused by lack of exposure to sunlight,” Chepak told the Guardian. “It helps promote vitamin D production [and] has helped students be more alert and focused in school. Maybe something like this would be beneficial in reducing the risk of leukemia.”