Testosterone Positively Associated with Cognitive Performance in Men

New research bolsters the case that testosterone plays a vital role in brain function and that age-related declines in testosterone are associated with age-related declines in cognitive ability.

New research bolsters the case that testosterone plays a vital role in brain function and that age-related declines in testosterone are associated with age-related declines in cognitive ability.

A number of studies to date have found significant positive correlations between testosterone levels and cognitive performance among men in industrialized countries. Now, a study published in the American Journal of Human Biology finds a similar connection among Tsimane men in Bolivia.

Researchers from the University of California, Santa Barbara, and the University of New Mexico, Albuquerque, recruited 94 Tsimane men to participate in a cognitive battery and to provide both urine and blood samples.

The cognitive battery assessed short-term recall, long-term recall, digit span, semantic memory, and visual scan. The fluid sample tests assessed both testosterone levels and indications of immune system activity.

The study team intentionally chose a population with relatively low innate testosterone levels, relatively little formal schooling and relatively high pathogen and parasite loads to test the theory the correlation between testosterone levels and cognitive performance is peculiar to men in industrialized countries, who tend to have higher testosterone levels, more schooling and dramatically lower parasite and pathogen loads.

After using linear mixed-effects regression to control for age, years of schooling, Spanish fluency, and village residence, the researchers found that testosterone levels were positively correlated with short-term recall (β = 0.267, P = 0.018), long-term recall (β = 0.326, P = 0.005) and visual scanning (β = 0.306, P = 0.008).

Markers of immune activation were negatively associated with cognitive function, but they did not change the associations between testosterone and cognitive performance.

The authors of the study noted several potential limitations to their work but said that the strength of the association they found, even after adjusting for potential confounders, provided significant evidence that the association between testosterone and cognitive ability holds for all men and not just those living in highly developed nations.

They also speculated about the value of testosterone in building societies.

“Testosterone may help motivate both physical and cognitive capacities that were essential for extracting the difficult-to-acquire, high-quality resources upon which humans relied over evolutionary history,” they wrote.

A research review published 5 years ago in Frontiers in Neuroendocrinology cited more than a dozen studies that found significant associations between testosterone levels and Alzheimer’s disease (AD) in men and women and similar relations between testosterone levels and dementia in several kinds of animals.

“Although the majority of studies have identified a relationship between low testosterone and increased AD risk in men, most were unable to determine whether low testosterone contributes to the disease process or is merely a result of it,” the authors of that review wrote. “However, two complementary studies suggest low testosterone occurs prior to or in the early stages of AD pathogenesis, and thus likely acts a risk factor.”

There were, at the time that review was written, a few attempts to evaluate whether testosterone replacement therapy could reduce the risk of cognitive decline or even reverse it. Most of them found small-but-significant positive effects, but a few found no benefit, and all of them were too small, too short or too weak to provide anything like definitive answers.

The same holds true of research since 2009, though there is an ongoing trial conducted by researchers at the University of Pennsylvania and sponsored by the National Institute on Aging that should produce better evidence.