A recent study conducted by researchers at the University of California, Santa Barbara, reveals that men’s brains shrink in volume as the day progresses, only to recover overnight. This pattern of shrinking and regrowth is thought to be influenced by the ebb and flow of hormones throughout the day.
The study, which scanned the brain of a 26-year-old man 40 times over 30 days, showed a consistent decrease in brain volume by 8pm. The shrinkage was particularly notable in areas responsible for sensory and visual processing. By morning, the brain had regained its original size.
Testosterone, cortisol, and estradiol, three key hormones, were found to peak early in the day and decline as evening approached. According to Laura Pritschet, one of the researchers, “Males show this 70% decrease from morning to night in steroid hormones.”
The study found that gray matter, a critical component in processing memory, emotions, and movement, thinned over the course of the day, with an average volume reduction of 0.6%. Despite this measurable change, researchers remain cautious in attributing the brain’s size fluctuations directly to hormones.
Co-author Elle Murata stated, “We can’t say that it’s directly causing it,” though she emphasized that hormones do impact brain structure. This finding counters the long-standing belief that hormones predominantly affect female biology, underscoring their relevance to men’s brain health as well.
While this study was conducted on a single participant, it opens the door for further research into how daily hormonal cycles impact brain function. Researchers plan to explore how factors like sleep patterns may contribute to these daily changes in brain volume.
