By Marc Sorenson, EdD,  Sunlight Institute

Recent research shows that there is a higher risk of leukemia in countries that are at high latitudes in the north or low latitudes in the south. The risk is twice as high at these latitudes as at latitudes closer to the equator.[1] Dr. Cedrick Garland, one of the authors of the research, stated that “these 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.”

Since persons living far from the equator have much less exposure to the sun’s rays, due to shorter sunlight seasons and more cloudiness, the statement regarding vitamin D deficiency makes sense; UVB from sun exposure, or another source such as tanning lamps, is necessary to stimulate the skin to produce vitamin D—hence the association between latitude and vitamin D.

However, Dr. William B Grant sent me an interesting paper that leads me to believe that some things that seem to make sense may not necessarily be true. The paper showed that there was little difference among vitamin D levels in countries at different latitudes,[2] with levels being close to 20 ng/ml on average. This would lead me to believe that vitamin D was not the factor that caused the reduced risk of leukemia among the countries that received more sunlight.

We are then left to determine the cause of the reduced risk of leukemia in the sunny countries. There are really only two factors that come to mind. First, sunlight, through the eyes, stimulates the production of serotonin/melatonin, which have been associated with protection against cancer in some studies. Sunlight also stimulates the skin to produce nitric oxide and endorphin, which could have an impact.

Second, populations residing in areas closer to the equator are likely to have access to year-round fruits and vegetables, which have been shown to associate to a lower risk of cancer. Whatever the reason, this is one more example of better health among people who receive more sunlight. And remember, even those fruits and veggies need sunlight to thrive. So let’s safely embrace the sun.

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[1] Cuomo RE, Garland CF, Gorham ED, Mohr SB. Cuomo RE, Garland CF, Gorham ED, Mohr SB. Low Cloud Cover-Adjusted Ultraviolet B Irradiance Is Associated with High Incidence Rates of Leukemia: Study of 172 Countries. PLoS One. 2015 Dec 4;10(12).
[2] Jennifer Hilger, Angelika Friedel, Raphael Herr, Tamara Rausch, Franz Roos, Denys A. Wahl, Dominique D. Pierroz, Peter Weber and Kristina Hoffmann. A systematic review of vitamin D status in populations worldwide. Br J Nutr. 2014 Jan 14;111(1):23-45.

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