Is short duration sleep a problem or is it just disturbed sleep that leads to increased mortality risk? A personal exploration.
Last updated on 11th September 2018
It is clear that there is a U-shaped association between sleep duration and mortality, with both short and long sleep linked with increased death rates. This finding is underlined by two major recent research overviews - Gallicchio & Kalesan "Sleep duration and mortality: a systematic review and meta-analysis" and Cappuccio et al's "Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies". There is so much interesting that one could write about this, but this particular blog post is triggered by a personal query that I have. I try hard - and am mostly successful - to have a very healthy lifestyle. I eat well, exercise well, keep a sensible weight, don't smoke, don't drink excessively. "Boring" possibly, certainly pretty healthy. My question is "How dangerous is it for my health to deliberately limit how long I spend sleeping?" I've talked about this with a few friends and the typical answer is "Why would you want to limit your time in bed?" Obvious answer ... "Because I really like being up, awake & active. There are tons of interesting, worthwhile things that I want to do. If I can healthily manage on an hour's less sleep per night, that's seven extra hours available per week. That's like an extra working day!" But is this stupid in health terms?
Well short sleep is linked to increased mortality by a whole series of pathways. Grandner et al's paper "Mortality associated with short sleep duration: The evidence, the possible mechanisms, and the future" does a good job of teasing this out. He notes that short sleep has been linked with 7 of the 15 leading causes of death in the US (cardiovascular disease, malignant neoplasm, cerebrovascular disease, accidents, diabetes, septicemia, and hypertension) and he discusses a variety of the best researched links including obesity, sleep apnea, physiological stress, immune changes & socioeconomic factors. As pretty much always when there is an association (here between short sleep & increased mortality), links include short sleep causing poor health, poor health causing short sleep, and poor health & short sleep both being caused by some other factor. And (also as one so often finds) it is very likely that all three of these pathways are relevant.
For somebody wanting deliberately to sleep less, it seems important to watch out for some of the obvious short sleep/increased mortality red flags. These include obesity, high blood pressure, psychological distress, and increased low grade chronic inflammation. In other words, if one is living healthily & well in other areas of one's life, it's pretty certain that shortening sleep duration is a safer procedure than if one is cutting corners or is unhealthy in other areas. Fascinatingly, high wellbeing too seems partly protective against damage from shorter time sleeping - see, for example, Friedman's recent paper "Sleep quality, social well-being, gender, and inflammation: an integrative analysis in a national sample" with its finding that social engagement protects against unhealthy inflammatory changes otherwise associated with shorter sleep. The author concludes "These results extend our previous work and bolster the suggestion that positive psychological functioning may compensate for other risk factors in predicting advantageous profiles of biological risk in aging adults."
This is an encouraging point. It links too with the finding that much of the research links increased mortality to insomnia not just to short sleep. Insomnia involves a complaint of difficulty initiating and/or maintaining sleep and/or non-restorative sleep. Crucially the diagnosis also demands that there be "associated marked distress & impairment in social or occupational functioning". Clearly people sleep for shorter periods than average for a whole series of reasons. Leger & colleagues, in their recent paper "Short sleep in young adults: Insomnia or sleep debt?", wrote "Short sleepers were defined as sleeping <6h a weekday (sleep+nap+pauses) ... Among short sleepers, 16% had insomnia, 45% sleep debt, and 39% neither ... Short sleepers had higher Epworth sleepiness scale scores (7.8 vs 6.7) ... Short sleep is highly prevalent in young adults but is not an homogeneous group, including both insomniacs and subjects with or without sleep debt." It's straightforward to check one's scores on the Epworth sleepiness scale and this gives a good indication of whether one is running a significant "sleep debt".
A particularly important recent paper, throwing light on all of this, is the study by Chandola et a - "The effect of short sleep duration on coronary heart disease risk is greatest among those with sleep disturbance" - with its abstract reading "Short sleep duration is associated with increased CHD (coronary heart disease) mortality and morbidity, although some evidence suggests that sleep disturbance is just as important. We investigated whether a combination of short sleep duration and sleep disturbance is associated with a higher risk of CHD than their additive effects ... PATIENTS OR PARTICIPANTS: The Whitehall II study recruited 10,308 participants from 20 civil service departments in London, England. Participants were between the ages of 35 and 55 years at baseline (1985-1988) and were followed up for an average of 15 years ... MEASUREMENTS: Sleep hours and sleep disturbance (from the General Heath Questionnaire-30) were obtained from the baseline survey. CHD events included fatal CHD deaths or incident nonfatal myocardial infarction or angina. RESULTS: Short sleep duration and sleep disturbance were both associated with increased hazards for CHD in women as well as in men, although, after we adjusted for confounders, only those reporting sleep disturbance had a raised risk. There was some evidence for an interaction between sleep duration and sleep disturbance. Participants with short sleep duration and restless disturbed nights had the highest hazard ratios (HR) of CHD (relative risk:1.55). Among participants who did not report any sleep disturbance, there was little evidence that short sleep hours increased CHD risk. CONCLUSION: The effect of short sleep (< or = 6 hours) on increasing CHD risk is greatest among those who reported some sleep disturbance. However, among participants who did not report any sleep disturbance, there was little evidence that short sleep hours increased CHD risk".
As Oscar Wilde put it so pithily "The truth is rarely pure and never simple." And what's my current view on whether I can get away with shorter sleep and stay healthy? The answer seems to be "Probably". If I keep a healthy lifestyle and high levels of wellbeing, then it seems reasonable to experiment with short sleep duration. I'm tracking my sleep on the useful website "Sleepio". I'm also tracking my daytime functioning (energy, effectiveness, irritability, wellbeing, etc) using a simple 0 to 10 scale (I already score well on the Epworth), with 0 anchored at "very poorly for me" and 10 at "very well for me". I'm experimenting on how well I do on 5 hours sleep a night. So far - two weeks in - the answer is "Pretty damn well."
And returning again to this blog post after a couple of months ... I've been charting my sleep & my day time function carefully. Adding in the occasional weekend lie-in and other changes in routine, I average about 5 hours 40 minutes in bed of which 5 hours 10 minutes are asleep. This makes me over 90% sleep efficient (better than it was before I started this experiment). Meanwhile my daytime functioning has held up well.