800 words

The black-white prostate cancer gap: genetic? Environmental? Both? Over the years, countless studies have been carried out—mostly on testosterone—to find the cause of the disparity between American blacks and whites.  Numerous research has shown that black Americans’ test is substantially higher than white Americans (Ross et al, 1986; Winters et al, 2001; etc). However, studies with larger samples showed this was not the case. In a sample of 3,654 whites and 585 black Vietnam veterans shows there is a 3 percent difference favoring blacks (Ellis and Nyborg, 1992). The gold standard—a meta-analysis on 14 relevant studies (which I will discuss tonight) shows that the difference in (free) testosterone is nowhere near what Ross et al (1986) say, but was substantially lower at 2.5 to 4.9 percent (Richard et al, 2014). The meta-analysis, which was done due to the conflicting figures in each study showed that the gap in testosterone.

Obviously these people weren’t genotyped for racial ancestry, so the authors included studies that only included racial descriptors:

If races/ethnicities included in the study were referred to as ‘black’, ‘African-American’, ‘non-Hispanic black’, ‘white’, ‘non-Hispanic white’ or ‘Caucasian’. We did not include men of Hispanic or Asian origin.

Since we know that self-identified race is an almost perfect predictor of genetic ancestry, and the meta-analysis included studies that used the only the descriptors for race/ethnicity then the fact that this is done on American sample shows that testosterone is not as high as commonly thought in blacks when compared to whites (13 percent higher free testosterone).

In this sphere, one of the most common things said is that testosterone is one of the biggest causes of the black-white crime gap. High levels of testosterone ARE linked to higher crime rates, and  blacks commit the most crimes, therefore blacks MUST have substantially higher levels of testosterone to account for the difference, right? Wrong. As I’ve shown above, Richard et al (2014) show that even after controlling for age, the difference in free testosterone was 2.5 to 4.9 percent. Black American males have an annual death rate from prostate cancer 2.4 times higher than whites (Taksler, Keating, and Cutler, 2012). If testosterone—one of the main possible culprits—does not explain the higher rate of prostate cancer mortality in American blacks in comparison to whites, what does?

Diet/environment and smaller genetic effects. People who have lower income cannot afford high-quality food, so they, therefore, have to buy low-quality, high carb, highly processed foods which lead to nutrient deficiencies. Drewnowski and Specter (2004) showed that 1) the highest rates of obesity are found in populations with the lowest incomes and education (correlated with IQ); 2) an inverse relationship between energy density and energy cost; 3) sweets and fats have higher energy density and are more palatable; and 4) poverty and food insecurity are associated with lower food expenditures, lower fruit and vegetable intake, and lower-quality diet. All of these data points show that those who are poor are more likely to be obese due to more energy-dense food being cheaper and fats and sugars being more palatable.

One important nutrient that people are often deficient in is vitamin D. Due to the name, people assume it’s a vitamin. It’s really not.  It’s a steroid hormone. Vitamin D promotes calcium absorption, maintains normal calcium and phosphate levels, promotes bone and cell growth, and reduces imflamation. Black Americans have numerous ailments that are associated with low vitamin D intake.

Black Americans have a lower intake of vitamin D in comparison to white Americans. This is due to low dietary intake of vitamin D and less sun exposure. Dark skin pigmentation reduces vitamin D production in the skin, as dark skin requires more sunlight in order to produce vitamin D. Rickets is a common a common problem for blacks as when the mother is pregnant, she doesn’t get sufficient vitamin D so when the baby is born, it is deficient.

One variable that Dr. Joseph Mercola brings up is that black women don’t breastfeed as much as white women (though the gap is beginning to close a bit) causing rickets (as well as the lack of availability of vitamin D for the baby due to darker skin needing more sunlight to acquire adequate vitamin D).

Pretty much a great case for why race and geography should inform vitamin D intake. This is pivotal for our understanding for racial/ethnic differences in disease acquisition, why these differences occur and what can be done to prevent them.

Elevated levels of testosterone in black men comparison to white men are supposed to explain the higher rate of mortality in black men compared to white men. Except Richard et al (2014) showed that the testosterone gap wasn’t as high as previously thought (at 2.4 to 5.9 percent higher). The deficiency in vitamin D explains this phenomenon. Low vitamin D is linked to aggressive prostate cancer. This is the cause for the disparity, not higher rates of testosterone.