Sleep Regularity Linked With Better Cognition, But Balance Patterns Best for BDNF
While regularity in day-to-day sleep patterns appears beneficial for cognitive function, sleep patterns that are rigid or highly regular may not be optimal in terms of serum brain-derived neurotrophic factor (BDNF), a key marker of cognitive function, according to a study published in Sleep Medicine.
The finding stemmed from an analysis of 458 participants, aged 45 to 89 years, from the Tsukuba Happiness Life Study in Japan. All participants had reported subjective concerns about cognition and sleep but were otherwise relatively healthy.
Researchers investigated associations between sleep irregularity, measured by the 100-point Sleep Regularity Index (SRI), and cognitive function. Participants wore a 3-axis accelerometer continuously for 7 days and underwent a standardized cognitive assessment battery. Additionally, blood samples taken from 232 participants measured levels of BDNF, a protein essential for synaptic plasticity and thought to protect against dementia in Alzheimer disease (AD) pathology.
SRI scores, which increase with greater sleep regularity, ranged from 10.86 to 85.59 among participants, according to the study. Participants with higher SRI scores (ranging from 65.35-85.59) showed higher global cognitive function compared with those with lower SRI scores (ranging from 10.86-54.08) after adjustment for demographic factors and total sleep time.
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“Besides excelling in physical activity, our participants with greater sleep regularity also tended to experience better sleep quality and began daytime activity earlier than those with irregular sleep patterns,” wrote corresponding author Jaehoon Seol, PhD, of the University of Tsukuba, Tsukuba, Ibaraki, Japan, and study coauthors.
The study also identified a nonlinear, inverse U-shaped relationship between SRI scores and serum BDNF levels. Maintaining a balanced SRI score of around 60 was associated with significantly higher serum BDNF levels compared with lower or extremely high SRI scores.
Although unexpected, the finding aligns with another study that found reduced gray matter and hippocampal volumes when SRI scores strayed in either direction from a median of 60, the authors noted.
“These findings collectively suggest a potential nonlinear relationship between day-to-day sleep patterns and AD pathology, yet the underlying mechanisms remain unclear,” they wrote.
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