Oversleeping or undersleeping are both linked with shorter lifespans; however, research involving over 90,000 adults shows that some of its harmful effects can be reversed with physical activity. An increase in physical activity levels was found to lower mortality risks associated with inadequate or excessive sleep duration.
Fitness and sound sleep both help extend life expectancy; however, their interaction with one another in terms of improving health has yet to become evident.
Early research was limited by using subjective self-reports of sleep and physical activity that may not be accurate, while an accelerometer device measures movement to provide objective and more reliable estimates of both duration and physical activity levels.
This study employed accelerometry to examine the combined effects of sleep duration and physical activity on risk of death among 92,221 participants aged 40-73 who donned an accelerometer wristband for one week.
Sleep durations less than 6 hours were classified as short; 6 to 8 hours as normal; and over 8 hours were defined as long. Physical activity volume was divided into low, intermediate, and high tertiles according to WHO guidelines for physical activity of moderate-vigorous intensity.
Death registries provide mortality data, with deaths from all causes being the primary outcome, while deaths due to cancer or cardiovascular disease were secondary outcomes.
Participant average age was 62 and just over half were women. Over an average follow-up period of seven years, 3,080 individuals died – 1,871 due to cancer and 1,074 from cardiovascular disease.
Examining the effects of physical activity on mortality was studied, first by looking at its volume then intensity.
Factors which could impact on this association were taken into consideration, including gender, age, ethnicity, education level, deprivation levels, sleep measurement season/shift work arrangements, diet/BMI levels/alcohol consumption levels/smoking habits.
Short and long sleep duration were associated with 16% and 37% increased risks of death from all causes in participants with low activity levels, respectively.
Short sleep duration was associated with an increased 41% risk of death from all causes among individuals with intermediate exercise levels; its length did not correlate to this risk in individuals who engaged in more vigorous physical activities. Sleep duration did not have an association with mortality risk in people engaged in high exercise levels.
Short sleepers with low exercise levels experienced a 69% increased cardiovascular death risk; this risk could be reduced when their levels increased to moderate or high exercise levels; for long sleepers, low levels led to a 21-13% increased cancer death risk that was eradicated with moderate or high exercise levels.
Similar outcomes were also seen with physical activity of moderate to vigorous intensity, with short and long sleep associated with 31% and 20% increased risks of death from all causes among those not meeting WHO recommendations respectively.
These risks were neutralized for those following WHO guidelines; short sleepers not reaching intensity of exercise recommendations experienced a 52% increase in cardiovascular death risk which was cancelled out when following these recommendations.
Long sleepers not meeting WHO recommendations had a 21% increased cancer death risk that was completely mitigated when following them.
These findings suggest that efforts promoting health that address both sleep duration and physical activity could be more successful in delaying or preventing middle-aged and older individuals from dying prematurely than simply targeting one behavior alone.
An ideal scenario would see individuals enjoying both physical activity and restful sleep at appropriate levels, however this study demonstrates that getting enough exercise may partially offset any detrimental impacts from too little or too much rest.
