Introduction
Restorative sleep is crucial for cognitive, emotional and behavioral performance and general human well-being. Handedness has been discussed as one factor affecting sleep among various others including age, body mass index (BMI) and sex. Being the preferred use of one hand over the other, handedness has been linked to physiological traits like memory function and pathological conditions like psychiatric disorders. While several studies investigated potential associations between handedness and (mostly subjective) sleep, large-scale studies including a broad age span of participants and studies analyzing women and men separately are lacking. In addition, there are only few studies determining objective sleep. These studies provided inconsistent results.
Objectives
Therefore, the aim of this study was to examine associations between handedness and both objective and subjective sleep in a large cohort with a broad age range from 18 to 80 years. In addition, the aim was to address potential endocrine effects by comparing associations in women and men as well as in premenopausal and postmenopausal women.
Methods
A subset of the approximately 10,000 participants from the population-based study “LIFE-Adult” (Leipzig Research Center for Civilization Diseases – adult group) was analyzed with regard to their handedness, objective and subjective sleep and important co-factors. Objective sleep data were determined using at-home actigraphy from 1764 healthy participants (18 to 80 years, 908 women), averaging five consecutive nights. 1024 individuals receiving acticraphy had been previously excluded for not meeting any of the in- and exclusion criteria. Only data collected in nights prior to work days were used. In addition, subjective sleep-related data were captured by self-report diaries, the Pittsburgh Sleep Quality Index (PSQI), the Epworth Sleepiness Scale (ESS) and the Morningness-Eveningness-Questionnaire (MEQ). Handedness was determined using the Edinburgh Handedness Inventory (EHI). The EHI provides information on the direction (i.e. left vs right) and the degree of handedness (i.e. strong vs weak). To address potential endocrine effects, premenopausal women (≤45 years) and postmenopausal women (≥55 years) were analyzed separately. This was also done for men, leaving four subgroups: young females (N=190), young males (N=137), female seniors (N=511) and male seniors (N=519) in order to compare pre- and postmenopausal age groups. Subgroups were compared using t-Test and correlations between sleep parameters and handedness were calculated using Spearman rank correlations.
Results
The degree and direction of handedness were correlated with “wake after sleep onset” (WASO) in the total sample and all women (the more right-handed/lateralized the shorter WASO). In postmenopausal women, additionally, time in bed (TIB) and total sleep time (TST) were positively correlated with right-handedness/higher lateralization. There were no other significant associations between an objective sleep variable and handedness. In both premenopausal women and >55-year-old men subjective quality of sleep (PSQI) was correlated with direction and degree of handedness, i.e. the more right-handed/lateralized the better. In the total sample and postmenopausal women, the degree and the direction of handedness were negatively correlated with daytime sleepiness, i.e. the less right-handed/lateralized the higher the daytime sleepiness. The chronotype was not associated with handedness in any group.
91% of participants were classified as RH with a very high degree of lateralization that was lower in non-RH participants. 5.4% of the women and 4.1% of the men were left-handed, 3.6% of the women and 4.8% of the men were ambidextrous as defined by the EHI-Score (EHI > 50 as RH, EHI < -40 as LH).
Discussion
To my knowledge, this is by far the largest study investigating the association between handedness and objective and subjective sleep. Most essential findings are, that right-handedness and higher lateralization both are associated with the following:
a) less WASO in the whole group, all women and postmenopausal women
b) more TIB and TST in postmenopausal women
c) better subjective quality of sleep in premenopausal women and >55-year old men
d) less daytime sleepiness in the total group and postmenopausal women
Thus, overall, while associations were not consistently found in all groups, right-handedness tended to be associated with better sleep and less daytime sleepiness. Overall, associations were weak, though. The finding, that direction and degree of handedness showed similar correlations, is plausible, since the vast majority of participants were right handed and showed a high degree of lateralization.
Results of this study are met by a relatively small body of literature, as only 11 studies were conducted on the association between handedness and sleep so far.
Out of these, four used objective measuring techniques on young participants exclusively (mean ages from 20.5 to 22.4 years), delivering a rather inconsistent picture. For example, while longer or shorter TST was found to be associated with right-handedness, other studies could not find an association at all. Also findings from our study do not show a homogenous picture. Overall, however, direction and degree of handedness (the more right-handed and the more lateralized) were associated with better objective sleep, being roughly in line with most of the studies. In contrast to these, however, our study is the first one to include participants over 30 years of age.
Comparably, out of the seven studies focusing on subjective sleep, all but one included participants younger than 30 years. Findings here mostly indicated, that right-handedness or higher lateralization are associated with better subjective sleep (e.g. longer TST, less WASO, fewer sleep problems). The only study targeting older participants did not find differences in the proportion of individuals agreeing to the question, whether they “can get enough rest and sleep”. Thus, our study is overall in line with the studies in younger adults.
Importantly, our study is the first to explore the relationship between handedness and daytime sleepiness. Here, right-handedness and higher lateralization were associated with less daytime sleepiness. This finding is in line with the idea that it may be more stressful and exhausting for non-RH coping in a right-handed world.
While we did not find striking differences between women and men or between pre- and postmenopausal women, several indications might suggest endocrine influences: For example, TIB and TST were positively correlated in postmenopausal but negatively in premenopausal women. Such findings warant further research on the influence of sex hormones on both handedness and sleep.
Conclusion
Although associations found in this study were not consistent in all subgroups, a trend towards right-handedness and higher lateralization being associated with aspects of better objective and subjective sleep as well as less daytime sleepiness became apparent. Seemingly differing associations between women and men are in line with endocrine interactions. Degree and direction of handedness seem to be equally important and should both be considered in future research.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:87807 |
| Date | 01 November 2023 |
| Creators | Taubert, Hilde |
| Contributors | Universität Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | urn:nbn:de:bsz:15-qucosa2-883780, qucosa:88378, qucosa:88378 |
Page generated in 0.0017 seconds