[sooheon]

If you skim the paper you will see they did multiple studies, including in humans. Including epidemiological studies and interventions like you mentioned. Which is why this is a well conceived paper, imo.

Testosterone is increased for men living in areas with high UV radiation, but only during summer time.

Proteins upstream of sex hormone production were upregulated after just a single day of 25m of bright midday sun exposure in both men and women.