Please note that "data were restricted to observations obtained on men of age 45–79 yr born between 1916 and 1945" and that this is a longitudinal survey with t

Please note that "data were restricted to observations obtained on men of age 45–79 yr born between 1916 and 1945" and that this is a longitudinal survey with three sets of sample collection times dating from 1987 to 2004. Also in the absence of longer-term or non-American data, we don't know if this is a decline from 'normal'. There's a lot of weird chemicals out there nowadays with biological effects, but there were a lot of those in the 20th century too. What I mean is, maybe instead of 'testosterone levels are low today because of all the soy', it's 'testosterone levels were inflated back then because of leaded gasoline (or DDT or asbestos or ....)'.