A total of 3055 men (mean age 76.4 y) and 3052 women (mean age 83.6 y) had actigraphic data of sufficient quality to be included in these analyses (98% and 95% of the sample studied respectively). On average, nocturnal sleep duration (mean ± SD) was 384 ± 74 min for the men in MrOS and 405 ± 78 min for the women in SOF. In these elderly cohorts, mean sleep duration was similar on weeknights versus weekends (381 min vs. 390 min in MrOS and 404 min vs. 407 min in SOF). Baseline data on each cohort by nocturnal sleep duration are shown for men in and for women in . Among both men and women, short sleepers (< 5 hours) were more likely to have co-morbidities. Antidepressant use was more common among both short and long sleepers. Among men, short sleep was associated with lower levels of education and greater rates of cigarette smoking. In both genders, short sleep duration was associated with increased prevalence of sleep apnea and symptoms of sleepiness. In contrast, no clear association was found between sleep duration and insomnia symptoms.
Demographic characteristics among men in the MrOS cohort by sleep duration.
Demographic characteristics among women in the SOF cohort by sleep duration.
In both men and women, mean BMI was greatest in those sleeping the least (). In multivariable analyses, mean BMI was 2.48 kg/m2 (95% CI: [2.02, 2.93]) greater in men and 1.75 kg/m2 [1.09, 2.42] greater in women among those sleeping less than 5 hours compared to those with 7–8 hours of sleep (p<0.0001 for both men and women). Short sleepers were also found to have greater waist circumference (). Relative to 7–8 hour sleepers, men sleeping less than 5 hours had a 6.7 cm [5.4, 8.0] greater waist circumference while in women this difference was 5.4 cm [1.0, 9.9] (p<0.0001 for men and p<0.02 for women). Hip circumference was 4.7 cm [3.7, 5.7] and 5.0 cm [1.0, 8.9] greater in short sleepers in men and women respectively (p<0.0001 for men and p<0.02 for women).
Association between body mass index and sleep duration among older men and women
Association between waist circumference and sleep duration among older men and women
Results from men in MrOS, for whom DXA measures of total and body regional fat were obtained, suggested the increases in these measures were due to increases in fat mass (). Percent body fat was 1.7% [1.1, 2.4] greater and percent body fat in the trunk was 1.9% [1.1, 2.7] greater in those sleeping less than 5 hours compared to those with 7–8 hours of sleep (p<0.0001 for both comparisons). In fact, the relationship between percent body fat and sleep duration exhibited a U-shaped association such that compared to those with 7–8 hours of sleep, men sleeping 8 hours or more had 0.9% [0.1, 1.7] greater overall percent body fat (p=0.03) and 1.2% [0.3, 2.1] greater percent body fat in the trunk (p=0.01).
Association between percent body fat and sleep duration among older men
Short sleep durations were also associated with increased likelihood of obesity (). Relative to those sleeping 7–8 hours, men sleeping less than 5 hours were 3.7 [2.7, 5.0] times more likely to be obese and women sleeping less than 5 hours were 2.3 [1.6, 3.1] times more likely to be obese. The odds ratios for obesity associated with sleeping 5–7 hours were 1.5 [1.2, 1.9] and 1.3 [1.0, 1.6] for men and women respectively.
Association between sleep duration and obesity among older men and women.
In order to assess whether the association between sleep duration and obesity was explained by sleep apnea, secondary analyses were performed adjusting for AHI (). Among men, the odds of obesity increased 1.4-fold [1.3, 1.5] with every 10 unit increase in AHI. Adjusting for AHI attenuated the association between short sleep and obesity by 18%; however, a significant association persisted. Mean BMI was 2.03 kg/m2 [1.57, 2.48] greater and the odds ratio for obesity was 3.0 [2.2, 4.2] in those sleeping less than 5 hours compared to 7–8 hour sleepers. Additional analyses were performed restricting to those individuals with an AHI < 15. In this subgroup, short sleep remained associated with greater adiposity. Among men, mean BMI was 1.99 kg/m2 [1.36, 2.63] greater among short sleepers and the odds ratio for obesity in short sleepers was 2.7 [1.6, 4.5]. Although the sample size was much smaller in SOF due to the limited number of sleep studies performed, the patterns were very similar in women (i.e., the association between short sleep and obesity was attenuated by 14% after adjusting for AHI).
Among men, neither daytime sleepiness nor insomnia symptoms were associated with obesity after controlling for sleep duration. Stratified analyses found similar associations between short sleep and obesity in men with and without excessive daytime sleepiness and with and without insomnia (). Among women, sleepiness was also not associated with obesity but insomnia was an independent predictor with an OR of 1.3 [1.1, 1.6]. In stratified analyses, the association between short sleep and obesity appeared stronger among women with daytime sleepiness and women with insomnia. However, formal statistical testing of an interaction between daytime sleepiness and sleep duration or insomnia and sleep duration was not significant.
Association between sleep duration and obesity among older men and women stratified by self-reported sleep symptoms.
Using total sleep time over the 24-hr period as the sleep duration measure instead of nocturnal sleep time had no substantial effect on the relationships found. In multivariate models, mean BMI was 1.54 kg/m2 greater [1.10, 1.97] among men and 1.23 kg/m2 greater [0.56, 1.90] among women with a 24-hr sleep duration less than 6 hours compared to 7–8 hours (p<0.0001 for men and p<0.001 for women). The odds ratios for obesity in those sleeping less than 6 hours relative to those sleeping 7–8 hours were 2.4 [1.8, 3.2] and 1.7 [1.2, 2.4] in men and women respectively. The association between nocturnal sleep duration and obesity measures was similar when restricted to data obtained on weeknights (data not shown).