I suggest the findings of Xu, et al., are caused by increased testosterone within urban populations. A report comparing rural areas and a large city found that testosterone is higher in the large city (Folia Histochem Cytobiol. 2001;39 Suppl 2:38-9).

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, diabetes, 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.

Conflict of Interest:

None declared