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Comment by Reason077 | Hacker News Reader

Perhaps you missed the part where they controlled for "confounders—including year of study, age, race, BMI, comorbidity status, alcohol and smoking use, and level of physical activity"

So, after correcting for BMI, physical activity, etc, there was still a very significant decline in testosterone between 1999-2000 and 2015-2016.

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Yeah, but a few paragraphs later, we have this:

"According to Lokeshwar, potential causes for these declines could be increased obesity/BMI, assay variations, diet/phytoestrogens, declined exercise and physical activity, fat percentage, marijuana use, and environmental toxins."

My personal, totally unsupported hypothesis: society is simply kinder and gentler now. As evidenced by the high testosterone in prison populations, this hormone responds to environmental threats of potential violence.

> My personal, totally unsupported hypothesis: society is simply kinder and gentler now.

Loved reading that. I don't know if it's true, but I hope so.

It's probably not the case that testosterone being lower is a result of society being kinder and gentler, but that society is kinder and gentler as a result of the lower testosterone.

I didn't read it in the former way personally. Your sentence confused me at first with that assumption for you to disprove.

Well, there might be a positive feedback loop factor implied, even if other factors might affect the rise of kinder society and the decrease of testosterone.

That’s funny as the first time I heard about feedback loop was in college biology courses, when we were taught how women hormones interactions are modelizable.

I see that and I'm glad they included it, but ...

Was 1999-2000 that golden age when we all threshed the fields by hand and steered the plows on foot ?

I remember people being quite sedentary and obese then and I don't know that an activity comparison to 1999-2000 has any utility ...

EDIT: OK, I am thinking about this backwards - if, as I suggest, people were just as sedentary in the first period as they are in the second, then the T drop begs a different explanation. As you suggest, they also corrected for age.

So, perhaps, my instinct is wrong. I would still look very closely at the (adjusted, corrected) physical activity before drawing any other conclusions ...

1999-2000 is a period in the past when they had measurements.

I mean ideally they'd have huge numbers of testosterone samples from all of human history, but what are they going to do?

it's a reference point? The article isn't comparing to some platonic ideal of what men's testosterone levels should be...it's just pointing out a statistically significant decrease in those levels over a period of 20 years

There is something double strange about the p values.For the main effect, the broad based decline, p < 0.0001. But for the result for men at "normal" weight, 18.5 < BMI < 24.9, the p value is given as p< 0.05.

The first strangeness is that this hints at a much weaker effect. The second strangeness is reporting the p value rather than the effect size. I clicked the link to a pdf at the bottom of the article, but it is not the paper. shrug

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