William of Ockham lived in the 1300s. Nowadays he is remembered for being an early and frequent user of the principle that the simplest explanation of a problem is usually the correct one – a principle of parsimony or succinctness we know as Occam’s Razor.
I bring it up because of a New York Times article published on July 4, A Disease Without a Cure Spreads Quietly in the West. The article is about a disease called Valley Fever caused by a fungus found in soil in dry areas. According to the Centers for Disease Control and Prevention, it’s found in the southwestern U.S., Mexico, and parts of Central and South America. “At least 30% – 60% of people who live in an endemic region are exposed to the fungus at some point during their lives. In most people the infection will go away on its own, but for people who develop severe infections or chronic pneumonia, medical treatment is necessary.”
Back to the New York Times article:
The pending transfer [of inmates from two state prisons in California’s San Joaquin Valley] has underscored the complexities and mysteries of a disease that continues to baffle physicians and scientists. In Arizona, a study from the Department of Health Services showed a 25 percent risk of African-Americans with newly diagnosed valley fever developing complications, compared with 6 percent of whites.
“The working hypothesis has to do with genetic susceptibility, probably the interrelationships of genes involved in the immune system,” said Dr. John N. Galgiani, a professor at the University of Arizona and the director of the Valley Fever Center for Excellence, founded in 1996. “But which ones? We’re clueless.”
Memo to the U.S. medical community: Whenever a disease or condition is worse in African-Americans, Occam’s Razor suggests the problem is related to vitamin D deficiency. It’s a much simpler explanation than genetic susceptibility. The primary genetic differences between white and black Americans are the genes for skin color.
The biological impact of different skin colors is widely divergent vitamin D levels. The mean vitamin D level in U.S. whites is 70% higher than the mean level in U.S. blacks. In the U.S., vitamin D comes primarily from sunlight. For a given amount of sunlight, light skin produces more vitamin D than dark skin. This is an evolutionary adaptation to the lower levels of ultraviolet light that humans encountered as they migrated away from the equator and it has been repeatedly reported in scientific journals (a PubMed search on “vitamin D” and “health disparities” provides multiple examples.)
Valley Fever may have nothing to do with vitamin D levels, but given Occam’s Razor and vitamin D’s link to pneumonia, it’s a valuable clue.