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I showed in part I, that the oft-cited reason for racial differences in prostate cancer acquisition and mortality are not due to higher levels of circulating testosterone when comparing blacks to whites (Richard et al, 2014). I posited (and provided sufficient evidence) that the disparity could come down to differences in vitamin D between the races. Black Americans are far removed from their ancestral environment, living in a cooler area. Their pigmentation reduces vitamin D production in the skin, since blacks need a lot more sunlight to synthesize the hormone than whites do, and the main culprit is the environment: not getting enough sunlight (Harris, 2006). I will provide further evidence for the theory.
The etiology of prostate cancer is not known (ACA, 2016; Bashir, 2015). The cause for the disparity in racial differences in prostate cancer may possibly come down to circulating vitamin D levels, with sunlight playing a large role in the variance. Racial differences in prostate cancer were larger in areas with less sunshine (Taksler et al, 2013). However, it is not known whether getting more sunlight (though the problem would still be getting enough in places with low levels of sunlight) or supplementing with vitamin D will help close the gap. Vitamin D is relevant for lethal prostate cancer (Shui et al 2012), whereas Li et al (2007) showed that supplementing with higher rates of vitamin D, especially during the winter months, may be particularly beneficial to men with low levels of circulating vitamin D. A study on veterans showed that men who had prostate cancer AND the lowest levels of vitamin D were more likely to die than veterans who had higher levels of the hormone (Der et al, 2014). Murphy et al (2014) showed in a biopsy, that in black Americans, low levels of vitamin D were associated with increased the odds of prostate cancer acquisition during the biopsy.
Black Americans are significantly more likely than European Americans to suffer from and die from prostate cancer (Hardiman et al, 2016). A difference of over 8,000 genes were found to be expressed differently. Blacks also have higher rates of prostate tumors and higher grade tumors than do European men. The racial disparity in prostate cancer mirrors circulating levels of vitamin D in the blood between the races (Nelson et 2016). Prostate cells become less sensitive to vitamin D through loss of receptors or signaling molecules “that mediate vitamin D’s actions, or through changes in metabolic enzymes that synthesize or degrade vitamin D compounds” (Peehl and Feldman, 2013). Hardiman et al (2016) showed that there were over 3,000 genes that differed between blacks and whites. Due to the fact that blacks are living outside of their ancestral climes, this is a large mediator of the prostate cancer gap. Vitamin D deficiency can also explain a large variation of the black-white prostate cancer gap (Grant and Peiris 2011).
Along with direct measurement of circulating vitamin D in the bloodstream, we also have correlates. Hypertension is correlated with prostate cancer: blacks have higher rates of hypertension; obesity further exacerbates the problem. Blacks males are more likely to be obese (though barely, which is where the other environmental factors come in). Men suffering from two or more health problems linked to metabolic syndrome are more likely to get prostate cancer. Blacks are more likely to get metabolic syndrome.
Clearly, a large portion of the variation in prostate cancer acquisition and mortality can be attributed to environmental factors (vitamin D intake specifically). We can also look to East Asia and their increasing rates of prostate cancer as well (Chen et al, 2014; Zhu et al, 2014). There are no genetic changes in the past ten years to account for this, so the only culprit is diet. Our Americanized diets have been making it to East Asia recently and it’s having a negative effect on them. China’s obesity rate is dramatically increasing, along with their rates of prostate cancer acquisition. It seems that the Western diet could also play a part in racial differences in prostate cancer acquisition.
To be fair the non-significance of this result might be attributable to the small number (only four) of African nations in the analysis. A number of previous studies have actually found that people of African descent on average do have shorter CAG repeats than other peoples (Ackerman et al., 2012; Esteban et al., 2005; Kittles et al., 2001; Lange et al., 2008). However, whether this actually indicates anything about the life history strategy of different populations remains questionable. The two other androgen indicators for which African data was available follow a completely different pattern. For androgenic hair, Caucasians have the highest rate, followed by Asians, then Africans. For prostate cancer, Caucasians have the highest rate, followed by Asians and Africans, who do not significantly differ.
The difference comes down, mostly in my opinion, due to diet. You can see this by looking at rates of prostate cancer in populations that have adopted, or are current adopting our Western diet.
There is a good chance that environmental factors explain a large part of the variance in prostate cancer acquisition and mortality. I, of course, do not deny intrinsic genetic explanations or other hormonal imbalances, however this is the best explanation I’ve come across. The fact that sunlight dictates prostate cancer acquisition is a huge tell and should be further researched.
I used to be a proponent of the testosterone theory, however, Richard et al (2014) shows a 2.5 to 4.9 percent difference in free testosterone between blacks and whites, which they conclude, does not explain the disparity between the races. Hormones do matter, and hormones can and do vary individually and by group, which are mediated by diet. Once we find out which foods either hurt or help prostate cancer growth, then we can have better treatments for this disease for men of all races.
There are numerous ways in which prostate cancer can be mitigated, with diet obviously playing a large factor (Son, Aronson, and Litwin, 2005; Lin, 2015; Nelson, Demarzo, and Yegnasubramanian, 2014). Future studies researching the racial disparities in prostate cancer should take into account UV radiation from the sun, circulating vitamin D in the blood, and diet amongst a myriad of other variables (these three just stand out to me). Moreover, large-scalre cohorts should be undertaken to see what effects diet can have on the mortality of those suffering from prostate cancer, as possibly supplementing vitamin D to attempt to fight the disease
I haven’t completely discredited the notion that Rushton and Lynn may be correct on this variable, but I’m highly skeptical. Hormonal data doesn’t show it. Hormones like IGF-1 and androgen don’t show the differences between races that would lead you to believe that Rushton’s Rule applies here.
PP is at it again, citing the same studies, not providing primary sources, and not addressing what I say to him about hormones in regards to penis size. Hormones affect the body in different ways, and different races have different levels of hormones. This is what I will discuss today.
Insulin-like growth factor 1 (IGF-1) is a hormone that, as it’s name implies, is structurally similar to the hormone insulin. IGF-1 is “partly responsible for systemic GH activities although it possesses a wide number of own properties (anabolic, antioxidant, anti-inflammatory and cytoprotective actions).” Laron and Klinger (1998) showed that children with Laron syndrome who stopped receiving IGF-1 injections showed reductions in penile and testicular size and they returned to pretreatment serum levels. This shows the effects of IGF-1 on sexual organ size.
Knowing this about IGF-1, for Rushton’s theory to be plausible, Blacks would have higher levels, Asians the lowest, and whites in the middle, skewing towards Asians. Platz et al (1999) investigated whether there were racial differences in circulating IGF-1 and insulin-like growth factor-binding protein 3 (IGFBP-3). IGFBP-3 binds IGF-1 and 2, with a dysregulation of IGFBP-3 correlating with cancer. IGFBP-3 is the main transporter of IGF-1 and 2 in the blood stream. The researchers tested men whose self-described ancestry (we know that self-describer ancestry is a great proxy for race, having a 99.86 percent success rate) African American (63) a random sample of Asians and Caucasians (75 respectively) aged 45 to 78 years old. Caucasians had the highest levels of IGF-1 (224 ng/ml), Asians (208 ng/ml), and African Americans (205 ng/ml). The IGF-1:IGFBP-3 ratio was greatest in Caucasians and lowest in Asians. This study was carried out to see if IGF-1 had an effect on prostate cancer. The 13 percent difference in IGFBP-3 between blacks and whites may account for the higher levels of prostate cancer, as IGFBP-3 can control IGF-1 bioavailabilty.
PP also cites Ross et al (1986) showing that blacks have “19 percent higher testosterone”, attempting to use this as evidence for the theory in favor of an inverse relationship between brain size and penis size. He seems to think that total testosterone matters, when what matters is free testosterone.It’s also 15 percent circulating testosterone, 13 percent free testosterone in that one study. Free testosterone is biologically active, and is able to exert its effect by passing through a cell and activating its receptor. Speaking of free testosterone, in this meta-analysis of 23 studies on black-white differences in testosterone, Richard et al (2014) showed a 2.5 to 4.9 percent difference in free testosterone and concluded that that difference was not enough to account for the racial disparity in prostate cancer. So it’s either black Americans have lower levels of IGFBP-3 or diet/environmental factors that cause this racial disparity in prostate cancer, not testosterone.
Rohrmann et al (2007) showed that testosterone differences between blacks (n=363) and whites (n=674) did not noticeably differ (5.29 ng/ml and 5.11 ng/ml respectively). Mexican Americans (n=376) , on the other hand, showed a higher average rate (5.48 ng/ml) over both cohorts. Blacks had higher levels of estradiol than whites (40.80 pg/nl and 35.46 pg/nl respectively). Blacks also had a higher level of sex hormone-binding globulin (SHGB) (36.49 nmol/liter) than whites (34.91 nmol/liter) and Mexican Americans (34.91 nmol/liter). That may account for some of the racial disparity in prostate cancer, but it’s not testosterone (which shows that ‘higher levels of testosterone’ as PP says, isn’t proof of any racial differences in penis size).
The Kinsey data is nonrepresentative and nonrandom. We have comparative sizes for certain ethnies, and the only statistical difference is between Nigerians and Koreans and Czechs. Rushton and Boegart didn’t mention that blacks danced less than white college students, blacks are more prudish regarding nudity, more likely to have a prostitute as a sexual partner and less likely to want large families (Weizmann et al, 1990). A study on certain CAG repeats shows that Africans cluster with East Asians on two measures, contradicting Lynn’s hypothesis. French Army Surgeon, lol (see Weizman et al 1990 from above):
This work is filled with internal contradictions. For example, an average African Negro penis is said to be 7 3/4 to 8 inches long on p. 56, while on p. 242 it is stated that it “generally exceeds” 9 inches. Similarly, while the French Army surgeon announces on p. 56 that he once discovered a 12-inch penis, an organ of that size becomes “far from rare” on p. 243. As one might presume from such a work, there is no indication of the statistical procedures used to compute averages, what terms such as “often” mean, how subjects were selected, how measurements were made, what the sample sizes were, etc.
I think I’ve shown that there are no “””racial””” differences in size with the Veale et al 2014 study and the Orakwe and Ebuh (2007) study. As far as I see, two statistical differences exist between Nigerians and Koreans and Czechs. But there’s not enough “””quality data””” to say “this race bigger than that race”. To believe there are racial differences in penis size or that there is even an inverse relationship between penis size and brain size takes a huge leap of faith to believe.
There are, without a doubt, average differences in a lot of things between races; hormones being one of them. Any differences between races in IGF-1 have no effect on penis size (IGF-1 is, however, one reason why black girls reach menarche at a younger age than white girls. Will write more on that in the future.). Africans were more similar to Asians that Caucasians on two of the five androgen indicators that Dutton (2015) tested. The Kinsey data is nonrepresentative and nonrandom and that is what PP continuously references. I’m highly skeptical leading towards no based on my knowledge of hormones and how they work in the human body. Testosterone does not explain any racial differences in penis size, and does not explain any differences in prostate cancer acquisition (though, other hormones do).