• Well, it’s not so simple. Testosterone operates within ranges. There’s a range we consider healthy when we’re considering the typical serum testosterone level. This biomarker has a rather large range (one which I believe needs to be refined, but for the most part is adequate). This study noted that there was a decrease in the amount, but not a shift in range. Most individuals are not at the extreme edges of this range, and in fact falling in or out of the range is not a marker of reproductive function.

    In this same study they looked at other fertility markers such as FSH and LH (much more important for sperm function) as well as motility - these three are much better markers of fertility than testosterone is. There was no significant change in any of these, except as noted by the authors a short term (<6mo.) decrease in motility that seemed to disappear with time.

    The reason I mention all this is that I believe there is good reason for the authors to not focus on these findings. In fact, they recognize their existence and call it out in the results and discussion section. There is a reason it was excluded from the main abstract and the conclusion - these findings aren’t particularly notable if you understand how we measure fertility and sex hormone levels considered normal. On the other hand, we have ample evidence that anything increasing BMI and decreasing VO2 max are unhealthy - while both of these are often binned for simplicity purposes, we happen to know that any absolute shift affects health, whereas this is not the case with testosterone.