Sleep disorders such as insomnia, sleep apnea, and sleepiness may contribute to self-reported cognitive decline in women with multiple sclerosis (MS), a new study suggests.
Using data from more than 60,000 female nurses, a team found that patients who showed evidence of sleep disorders — cited as one cause of MS fatigue — tended to report worse cognitive function four years later. Among the cognitive problems reported by these women were difficulty in following instructions or conversations, and trouble navigating familiar streets.
“Perceived cognitive decline, even in the absence of objective changes, could be an important window of opportunity to identify treatable exacerbating factors, such as sleep disorders,” Tiffany Braley, MD, director of the MS Fatigue and Sleep Clinic at University of Michigan Health and lead author of the study, said in a university news story.
The study, “Pathways between multiple sclerosis, sleep disorders, and cognitive function: Longitudinal findings from The Nurses’ Health Study,” was published in the Multiple Sclerosis Journal.
Investigating sleep disorders using data from women with MS
Cognitive dysfunction is a common and disabling MS symptom, affecting up to 70% of those with the disease. However, therapies to improve cognitive function in MS patients have limited efficacy, which has prompted researchers to identify risk factors that can be targeted to reduce these symptoms.
Sleep disorders are disproportionately more common in people with MS than in the general population and have been associated with cognitive problems and worse quality of life.
Still, most studies focusing on sleep disorders in MS have looked at objective measures of cognition and not at perceived changes in cognitive processes. Also, studies have not addressed how MS and sleep problems interact to worsen cognitive function.
“We have previously identified important associations between objective cognitive performance and sleep in people with MS, but little is known about how sleep and MS interact together to impact long-term cognitive outcomes,“ said Braley, also the director of the division of multiple sclerosis and neuroimmunology at University of Michigan Health.
To assess if perceived cognitive changes in women with MS are mediated by sleep problems, researchers examined data from more than 63,000 female nurses, including 524 with MS. All are enrolled in the Nurses’ Health Study II, a long-term study focusing on risk factors for chronic diseases in women.
Participants included in the analysis were those who completed long-form questionnaires in 2013 and 2017. The questionnaires included questions intended to provide detailed information regarding sleep and cognitive function, among other several other clinical factors and lifestyle habits.
Overall, the study participants were, on average, 58.7 years old in 2013. Compared with nurses without MS, those with the neurodegenerative disorder had a higher prevalence of multiple sleep disorders, including obstructive sleep apnea (OSA) — a condition in which breathing is interrupted multiple times during sleep — insomnia, and excessive daytime sleepiness.
Cognitive function was assessed in the 2017 questionnaire through questions about three memory items: difficulty in understanding or following spoken instructions, recent difficulty in following a group conversation or a plot in a television program, and trouble in traveling on known routes while navigating places.
Regardless of sleep issues, people with MS were 2.2 times more likely to have difficulty following spoken instructions, and 1.9 times more likely to have trouble following conversation or plots. They also had a 2.7 times greater likelihood of experiencing issues in navigating familiar streets.
However, this effect of MS in cognitive function was somewhat mediated by sleep problems identified by nurses in 2013.
For example, insomnia mediated 5.4% of the total effect of MS on the ability to follow spoken instructions, 8.4% in the ability to follow conversations or plots, and 15.1% on memory problems.
For sleepiness, the impact was even greater: It mediated 8.6% of the total effect of MS on the ability to follow spoken instructions, 10.1% on the ability to follow conversations or a plot, and 12.3% on memory difficulties.
OSA accounted for 34% of the total effect of MS on the ability to follow spoken instructions, but had no significant impact on the other measures of cognition.
Our findings highlight sleep disorders as common potentially modifiable contributors to cognitive dysfunction in women with MS.
According to the researchers, these “findings suggest that prevalent OSA, insomnia symptoms, and sleepiness could differentially moderate or mediate the effect of MS on perceived cognition in women with MS, highlighting distinct direct and indirect associations between these disorders.”
Moreover, the results also suggest that early identification of cognitive symptoms — such as via self-reporting by patients — may help in getting any potential therapies started as early as possible.
“Interventions to delay cognitive decline in MS may be of highest yield in pre-symptomatic or early symptomatic stages,” the team wrote.
“Our findings highlight sleep disorders as common potentially modifiable contributors to cognitive dysfunction in women with MS,” they concluded.