A Biological Explanation of the Increase in Type 2 Diabetes World-Wide


Copyright 2011, James Michael Howard, U.S.A. 


(A response to "The Lancet," 2011: "National, regional, and global trends in fasting plasma glucose and diabetes prevalence since 1980: systematic analysis of health examination surveys and epidemiological studies with 370 country-years and 2.7 million participants," Danaei, et al.)  The following is my explanation of the “secular trend” in the United States; I suggest the same explanation explains the increase in Type 2 Diabetes in the world.  It is known that type 2 diabetes is characterized by low testosterone.  I think this may be the cause.  In my explanation, I explain how an increase in testosterone within the population can result in reduced testosterone later in life.  Hence, the secular trend increases the effects of high testosterone early in life and low testosterone late in life, which includes type 2 diabetes.


"A syndrome is occurring in America and other countries, the cause of which is often attributed to one part or another of the syndrome, itself, and more often attributed to the environment or life style.  I suggest a single cause may be involved that is biological and evidence of ongoing evolution.  The cause may be increased exposure to maternal testosterone within the population with time.


It is my hypothesis that the "secular trend," the increase in size and earlier puberty occurring in children, is caused by an increase in the percentage of individuals of higher testosterone. More specifically, I suggest this is due to an increase in the percentage of mothers of higher testosterone with time within the population. This exposes more fetuses to increased maternal testosterone with time within the population. This causes permanent effects in the fetus which persist throughout the life span.  I suggest this is the cause of the parallel increases in morbidity occurring within the population, such as obesity, cancer, breast cancer, type 2 diabetes, the metabolic syndrome, etc., including prematurity, small for gestational age, etc., including less obvious gross effects which later contribute to "failing schools" and other adverse behavioral outcomes in children.


I have come to the conclusion that the "increase in testosterone" may partially be due to a reduction in "sex hormone binding globulin (SHBG)" as a number of phenomena explained by the secular trend may be based on changes in SHBG.   A decrease in SHBG increases free testosterone levels.  Low SHBG has been found in obese children who do not produce excessive testosterone.  A number of negative phenomena which may be caused by increased testosterone are found with low SHBG and a number of positive effects of reduced SHBG exist.


It is my hypothesis that human evolution is driven by increases in testosterone ("Androgens in Human Evolution," Rivista di Biologia / Biology Forum 2001; 94: 345-362).  This was directly supported by research in 2003; see the chart of testosterone levels in humans and related great apes, upper left at http://www.anthropogeny.com/ .  I suggest that periodically testosterone increases excessively and the exposure to excessive maternal testosterone causes negative and evolutionarily consequential changes to the human population.  We may be experiencing this effect at this time.


I suggest this increase in testosterone in the population peaks earlier with time.  This earlier peak may produce an earlier decrease in the population with aging.  A number of studies reported in the medical literature have identified low testosterone as a cause of currently increasing disorders.  Therefore, the secular trend may be causing increased morbidity and mortality as a result of excessive testosterone and low testosterone within the population.


As I have said before, I think women of higher testosterone drive the secular trend / human evolution.  I suggest these women produce the highest percentage of premature infants. It has been reported that "preterm boys" exhibit increased testosterone and the effects of increased testosterone compared to "full term boys" (J Clin Endocrinol Metab 2010, "Increased Activity of the Hypothalamic-Pituitary-Testicular Axis in Infancy Results in Increased Androgen Action in Premature Boys.," Kuiri-Hanninen, et al., J Clin Endocrinol Metab. 2011 Jan;96(1):98-105). What this means is that the population is increasing in women of higher testosterone and this group of women may also be increasing the percentage of men of higher testosterone simultaneously. This could explain why this "secular trend" can increase so rapidly. This mechanism could expand the percentage of these individuals within a population rapidly and drive human evolution."