testosterone levels have declined in most developed countries when comparing similar age cohorts over time. See the following studies: from Finland - https://w

testosterone levels have declined in most developed countries when comparing similar age cohorts over time. See the following studies: from Finland - https://www.ncbi.nlm.nih.gov/pubmed/23161753 https://www.ncbi.nlm.nih.gov/pubmed/23161753. from USA - https://academic.oup.com/jcem/article/92/1/196/2598434 https://academic.oup.com/jcem/article/92/1/196/2598434 it is a bit of a medical mystery because the trend cannot be fully explained by lifestyle factors like weight gain.