For women with multiple sclerosis who report cognitive dysfunction — one of the most common and disabling symptoms of the disease — sleep disorders such as insomnia and sleep apnea may contribute to the perceived decline, a new study suggests.

Past studies found that people with MS have a higher likelihood of sleep disorders, which have been shown to affect quality of life. As people with MS are at risk for sleep and cognitive problems, researchers sought to examine cognitive outcomes among nurses with MS and sleep disorders.

Researchers at Michigan Medicine, at the University of Michigan, analyzed data from more than 60,000 women using the 2013 and 2017 waves of the Nurses’ Health Study, a long-term study that focuses on risk factors for chronic diseases in women. Using composite scores of self-reported diagnoses and symptoms, they found that women with MS were more likely than those without MS to report sleep disorders, including obstructive sleep apnea, insomnia, and sleepiness.

Results also reveal that sleep disorders identified in 2013 contributed to cognitive problems reported by women with MS in 2017, including ability to follow instructions and conversations, as well as memory. Insomnia mediated more than 10 percent of these outcomes, and sleep apnea accounted for 34 percent of the total effect between MS and the ability to follow instructions.

Interventions to delay cognitive decline in MS may be most effective in pre-symptomatic or early symptomatic stages, the researchers said.

The study was published in Multiple Sclerosis Journal.