Sleep Duration, Survival, and Categories of Physical Activity
Sleep Duration, Survival, and Categories of Physical Activity
The association between long sleep duration and death is not fully understood. Long sleep is associated with low physical activity, which is a strong predictor of death. Our aim was to investigate the association between sleep duration and death across categories of total physical activity in a large prospective cohort of Swedish men and women. We followed a population-based cohort of 70,973 participants (37,846 men and 33,127 women), aged 45–83 years, from January 1998 to December 2012. Sleep duration and physical activity levels were assessed through a questionnaire. We evaluated the association of interest in terms of mortality rates by estimating hazard ratios with Cox regression and in terms of survival by evaluating 15th survival percentile differences with Laplace regression. During 15 years of follow-up, we recorded 14,575 deaths (8,436 men and 6,139 women). We observed a significant interaction between sleep duration and physical activity in predicting death (P < 0.001). Long sleep duration (>8 hours) was associated with increased mortality risk (hazard ratio = 1.24; 95% confidence interval: 1.11, 1.39) and shorter survival (15th percentile difference = −20 months; 95% confidence interval: −30, −11) among only those with low physical activity. The association between long sleep duration and death might be partly explained by comorbidity with low physical activity.
Several epidemiologic studies have described the association between sleep duration and death as a U shape, showing that those who sleep 7 hours/day have the lowest mortality rate. Although the negative effects of short sleep duration are widely accepted, concerns have been raised about the negative effects of long sleep duration and the underlying biological mechanisms.
Stranges et al. investigated potential factors that could confound or mediate the U-shaped association between sleep duration and death and found that low physical activity was strongly associated with long sleep duration, concluding that long sleep may represent an epiphenomenon of comorbidity. Two studies have recently evaluated the association between sleep duration and death according to physical function and health status, but they did not observe any modification in the association. To the best of our knowledge, no studies have been published on the association between sleep duration and death as modified by a score of total physical activity, summarizing in a single value different domains of daily physical activity (i.e., leisure time/exercise, work, housework). Our aim was to investigate the association between sleep duration and death across categories of total physical activity in a large prospective cohort of Swedish men and women.
Abstract and Introduction
Abstract
The association between long sleep duration and death is not fully understood. Long sleep is associated with low physical activity, which is a strong predictor of death. Our aim was to investigate the association between sleep duration and death across categories of total physical activity in a large prospective cohort of Swedish men and women. We followed a population-based cohort of 70,973 participants (37,846 men and 33,127 women), aged 45–83 years, from January 1998 to December 2012. Sleep duration and physical activity levels were assessed through a questionnaire. We evaluated the association of interest in terms of mortality rates by estimating hazard ratios with Cox regression and in terms of survival by evaluating 15th survival percentile differences with Laplace regression. During 15 years of follow-up, we recorded 14,575 deaths (8,436 men and 6,139 women). We observed a significant interaction between sleep duration and physical activity in predicting death (P < 0.001). Long sleep duration (>8 hours) was associated with increased mortality risk (hazard ratio = 1.24; 95% confidence interval: 1.11, 1.39) and shorter survival (15th percentile difference = −20 months; 95% confidence interval: −30, −11) among only those with low physical activity. The association between long sleep duration and death might be partly explained by comorbidity with low physical activity.
Introduction
Several epidemiologic studies have described the association between sleep duration and death as a U shape, showing that those who sleep 7 hours/day have the lowest mortality rate. Although the negative effects of short sleep duration are widely accepted, concerns have been raised about the negative effects of long sleep duration and the underlying biological mechanisms.
Stranges et al. investigated potential factors that could confound or mediate the U-shaped association between sleep duration and death and found that low physical activity was strongly associated with long sleep duration, concluding that long sleep may represent an epiphenomenon of comorbidity. Two studies have recently evaluated the association between sleep duration and death according to physical function and health status, but they did not observe any modification in the association. To the best of our knowledge, no studies have been published on the association between sleep duration and death as modified by a score of total physical activity, summarizing in a single value different domains of daily physical activity (i.e., leisure time/exercise, work, housework). Our aim was to investigate the association between sleep duration and death across categories of total physical activity in a large prospective cohort of Swedish men and women.