Fragmented sleep and low sleep efficiency has been linked to cognitive decline in older men, according to a recent study.

Researchers found that poor sleep quality was associated with a 40 to 50 percent increase in the development of cognitive decline over three to four years. This is was similar in magnitude to the effect of a five-year increase in age.

They also found, in contrast, that sleep duration was not related to subsequent cognitive decline.

"It was the quality of sleep that predicted future cognitive decline in this study, not the quantity," Terri Blackwell, lead author and senior statistician at the California Pacific Medical Center Research Institute (CPMCRI) in San Francisco, Calif., said in a statement. "With the rate of cognitive impairment increasing and the high prevalence of sleep problems in the elderly, it is important to determine prospective associations with sleep and cognitive decline."

For the study, researchers collected data from more than 2,800 community-dwelling older men at six clinical centers in the United States. Study participants had a mean age of 76.

 An average of five nights of objective sleep data were collected from each participant using a wrist actigraph. Cognitive function assessment included evaluation of attention and executive function using the Trails B test. Executive function is the ability for planning or decision making, error correction or trouble shooting, and abstract thinking, researchers explained in a press release. 

Their results were adjusted for potential confounding factors such as depressive symptoms, comorbidities and medication use.

"This study provides an important reminder that healthy sleep involves both the quantity and quality of sleep," Dr. M. Safwan Badr, researcher and American Academy of Sleep Medicine President. "As one of the pillars of a healthy lifestyle, sleep is essential for optimal cognitive functioning."

The underlying mechanisms relating disturbed sleep to cognitive decline remain unknown, the authors noted. They added that additional research is needed to determine if these associations hold after a longer follow-up period.

The findings were recently published in the journal Sleep.