I am not saying that I know for 100% that there is no decline in T levels after adjustment for BMI, disease, smoking etc.
I am saying that the literature is controversial on that topic and that one has to really carefully evaluate the databasis when interpreting the studies.’
'In two of the previous observational reports [2, 4] adjustment to body mass index (BMI) led to a nullification of the period-related changes in testosterone. However, in the other two observational reports [1, 3] the age-specific testosterone decline remained significant after adjustment to BMI.
‘In this analysis we did not adjust for BMI, as this is unclear whether BMI is a potential mediator or confounder since BMI has not been established as a sole explaining parameter in previous studies on longitudinal trends of testosterone. Analysis performed on the research population with available data on BMI showed little variation (< 1 kg/m2) in the mean age-specific BMI between study periods, with no discernible trend (data not shown). We therefore suggest that the observed testosterone decline is not likely to be explained by obesity trends.’
Thats interesting because Israel is experiencing almost the same increase in obesity rates as the US. In 2018 25% of the 15 year old males were obese. 50% of young men were overweight. In 2000 these numbers were 18% obese and 35% overweight.
It definitly needs to get thoroughly investigated because if this is true, whatever the cause may be, its scary.