African-Americans are 25 percent more likely to die from cancer than white Americans are, and the reasons are numerous, including lower socio-economic status, poorer access to health care, and the cancer diagnosis coming at later, more deadly stages.
Still, health experts say these factors cannot fully explain the extent of disparities in survival for the most common cancers, such as breast, lung, colon and prostate cancers.
A paper published in the current issue of the journal Dermato-Endocrinology points the finger at a seemingly obvious but overlooked culprit: the sun.
The researchers’ theory is that, in northern latitudes, the dark skin of African-Americans cannot absorb enough sunlight to generate adequate amounts of vitamin D, which is often called the “sunshine vitamin.” The body uses ultraviolet rays from the sun to manufacture vitamin D in the inner layers of the skin.
Vitamin D is needed for strong bones; doctors nearly 100 years ago associated a lack of adequate sun exposure with rickets among child laborers, exemplified by bowed legs. Recent studies also have shown that low levels of vitamin D in the blood seem to contribute to a weak immune system and a host of diseases, such as cancer and multiple sclerosis.
This lack of vitamin D could completely fill in the health disparity gap for cancer survival between white and black Americans, the researchers said.
Previous work by geneticist Rick Kittles at the University of Chicago suggests that upwards of 75 percent of African-Americans are deficient in vitamin D. Kittles says that African-Americans living north of the 37th parallel—just about anyplace north of central California, Texas, Tennessee or North Carolina—will have difficulty through most of the year absorbing enough sunlight to make vitamin D, because of the low angle of the rays reaching the Earth’s surface.