From the article:
Osvaldo P. Almeida, M.D., Ph.D., F.R.A.N.Z.C.P., of the University of Western Australia, Perth, and colleagues studied 3,987 men age 71 to 89 years.
[…]
A total of 203 of the participants (5.1 percent) met criteria for depression; these men had significantly lower total and free testosterone levels then men who were not depressed. After controlling for other factors – such as education level, body mass index and cognitive scores – men in the lowest quintile (20 percent) of free testosterone concentration had three times the odds of having depression compared to men in the highest quintile.
The mechanism by which low hormone levels might affect depression risk has not been identified, but might involve changes in the levels of neurotransmitters or hormones in the brain, the authors note.
“A randomized controlled trial is required to determine whether reducing prolonged exposure to low free testosterone is associated with a reduction in the prevalence of depression in elderly men,” the authors write.