SLEEP disorders have a significant effect on cognitive function in females with multiple sclerosis (MS). Tiffany J. Braley, Division of Multiple Sclerosis and Neuroimmunology at Michigan Medicine, University of Michigan, Ann Arbor, USA, stated: “We did not expect that the pathways by which sleep disorders exerted their effects on future cognitive problems in MS would vary based on the type of sleep disorder experienced.”
Braley and colleagues analysed 63,866 females (mean age: 58.7; 95.3% White) from the 2013 and 2017 Nurses’ Health Study, which included 524 females with MS. The researchers assessed subjective cognition by using items in a survey that assessed the nurses’ memory, their ability to follow instructions and conversations/plots, as well as street navigation. The research team used the ‘decomposition’ method (measuring controlled direct, reference interaction, mediated interactions, and pure indirect) to estimate the effects of suspected or diagnosed sleep disorders on the relationship between cognitive function and MS.
Before evaluating how different sleep disorders affected cognitive function, the researchers studied how MS was related to cognitive function. They discovered that it was linked to higher odds for trouble following verbal instructions, trouble following conversations/plots, trouble with street navigation, and memory difficulty.
Furthermore, each sleep disorder showed different levels of effects on cognitive function. Females with MS and obstructive sleep apnoea had increased odds for cognitive impairment when following instructions (adjusted odds ratio [OR]: 2.2; 95% confidence interval [CI]: 1.5–66.9), following conversations/plots (adjusted OR: 1.9; 95% CI: 1.2–2.7), and following street navigation (adjusted OR: 2.8; 95% CI: 1.1–4.4).
When looking at the effects that insomnia has on females with MS, the researchers discovered that the pure indirect effect mediated 5.4% on following instructions, 8.4% following conversations/plots, and 15.1% on memory problems.
There were comparable findings regarding pure indirect effect when assessing the effect that sleepiness has on cognition in females with MS. This effect mediated 8.6% on following instructions, 10.1% on following conversations/plots, and 12.3% on memory weakening.
Braley noted: “Studies that span longer timeframes and include both objective and self-reported cognitive outcomes, as well as objective sleep data, are still needed to fully characterise the relationship between MS, sleep disorders, and cognitive dysfunction.”