A research team from the University of California San Diego discovered that low sun exposure was associated with increased incidence rates of leukemia.
Leukemia is cancer of the blood forming tissues that often results in high numbers of abnormal white blood cells. In 2014, the U.S. had more than 50,000 new cases and 24,000 deaths from leukemia.
Multiple studies have suggested that vitamin D plays a role in leukemia. One study found that low vitamin D status was linked to lower rates of relapse-free survival. A case-control study reported that all patients with acute leukemia were vitamin D deficient, which was defined by levels less than 20 ng/ml (50 nmol/l).
Researchers recently conducted a study to test their hypothesis that “leukemia is due mainly to vitamin D deficiency, which is due mainly to low solar ultraviolet B (UVB) irradiance.”
They analyzed data from the International Agency for Cancer Research’s Global Cancer 2012 database, finding the age-adjusted leukemia incidence rates for 172 countries. The research team also used data from the International Satellite Cloud Climatology Project to look at the cloud cover-adjusted UVB irradiance for each country.
The researchers found that individuals residing at higher latitudes with lower sun exposure, such as the U.S., Australia, New Zealand, Canada and Ireland, were at least twice as likely to have leukemia as individuals residing in countries closest to the equator, such as Nigeria, Bolivia, Samoa and Madagascar. The inverse relationship between sun exposure and leukemia incidence rates remained significant after adjusting for potential confounding factors (p < 0.01).
The researchers concluded,
“Importantly, these results suggest that increased levels of UVB irradiance and vitamin D may help prevent development of leukemia.”
UVB exposure is the primary source of vitamin D, leading researchers to believe that vitamin D may be accountable for the link between low sun exposure and higher incidence of leukemia. However, one cannot rule out the possibility that a different byproduct of UVB exposure may be responsible for this relationship. It’s important to note that this was an epidemiological study, and the analysis was unable to control for the many confounders that may contribute for differences in leukemia risk between countries.
Tovey, A. & Cannell, JJ. Closer look: Low sunlight associated with higher risk of leukemia. The Vitamin D Council Blog & Newsletter, January 2016.