according to a new study in General Psychiatry.
The findings add to those seen in other observational studies showing afternoon napping promotes cognitive function, said the authors of the paper, published in General Psychiatry.
“The prevalence of afternoon napping has been increasing in older adults much more than in younger individuals,” wrote Han Cai, MS, of the department of geriatrics at The Fourth People’s Hospital of Wuhu, Anhui, China, and coauthors. “The elderly individuals who took afternoon naps showed significantly higher cognitive performance compared with those who did not nap.”
The researchers enrolled 2,214 people in the study – all Han Chinese and aged 60 or older. Afternoon napping was considered any period of inactivity of at least 5 minutes but less than 2 hours after lunch and outside of the person’s main sleep schedule. Those who reported ever napping – 1,534 subjects – were included in the napping group, and the others – 680 – in the nonnapping group. Patients with major physical conditions were excluded.
The Montreal Cognitive Assessment (MoCA), the Mini-Mental State Examination (MMSE), and the Neuropsychological Test Battery (NTB) were used to measure cognitive function, and 739 patients agreed to blood tests for lipid values.
The average total MMSE score was higher for the napping group at 25.3 points out of 30, than for the nonnapping group, at 24.56 (P = .003). Those in the napping group also had significantly higher scores in the orientation portion of the MoCA test, at 5.55 out of 6 points, compared with 5.41 for the nonnapping group (P = .006).
Those in the napping group scored significantly higher on the digit span and language fluency parts of the Neuropsychological Test Battery (P = .009 and .020, respectively).
Dementia was assessed with face-to-face visits with clinicians, but diagnoses of dementia were not different between the groups.
Triglycerides were found to be higher – though still in the normal range – in the napping group compared with the nonnapping group, 1.80 mmol/L to 1.75 mmol/L, the researchers found (P = .001). No differences were seen for HDL or LDL cholesterol levels, or in hypertension or diabetes, the researchers reported.
The authors noted that inflammation is likely an important feature in the relationship between napping and cognitive function. Inflammatory cytokines have been found to play a role in sleep disorders, and strong inflammatory responses can lead to adverse events, including cognitive impairment.
“Sleep is known to be a regulator of the immune response that counters these inflammatory mediators, whereas napping, in particular, is thought to be an evolved response to inflammation,” they said.
The average age of patients in the napping group was 72.8 years, slightly older than those in the nonnapping group at 71.3 years, and this was a significant difference (P = .016).
The researchers acknowledged that the study “could not show direct causality of napping, whether beneficial or harmful,” and that “a lack of detailed information regarding napping duration ... also limited the description of napping status.”
Junxin Li, PhD, RN, assistant professor at Johns Hopkins School of Nursing, Baltimore, who has studied napping and cognition, said that previous research generally supports a U-shaped relationship between napping and mental acuity, with shorter or medium-length naps benefiting cognition and no naps or naps that are too long being detrimental.
Dr. Junxin Li
“This study looked at no nap versus naps of less than 2 hours and may not be able to capture this potential U-shaped association,” she said.
For clinicians, the duration, timing, frequency, and purpose of naps are important factors in making recommendations to patients, she said.
“For example, timing – napping in the early evening close to older adult’s bedtime may delay their bedtime and interfere with their nighttime sleep quality. Taking naps after lunchtime is hypothesized to provide the most therapeutic values to the health and usually recommended,” she said. Regular napping is better than “randomly dozing off,” Dr. Li added.
There are also cultural considerations – in east Asia, napping tends to be considered part of a healthy lifestyle, while in western countries it is not – and this could impact napping behaviors and how these behaviors affect cognition, she said.
Phyllis C. Zee, MD, PhD, director of the Center for Circadian and Sleep Medicine at the Northwestern University, Chicago, said the results are consistent with early cross-sectional studies that showed that regular, scheduled naps in the afternoon were associated with positive cognitive performance and lower cardiometabolic disease risk.
Dr. Phyllis C. Zee
Dr. Zee noted that it’s important to recognize that the positive data are associated with naps that are planned, while older adults napping because of excess sleepiness are at a higher risk for cognitive impairment and other health issues.
The study authors, Dr. Li, and Dr. Zee reported no relevant financial disclosures.