I believe that lifestyle factors such as diet and exercise have potentially profound impact on health and wellbeing, and this is certainly reflected in the voluminous recommendations that come at us regarding what we should and shouldn’t be doing in these areas. However, I also take the view that another key lifestyle factor ” sleep ” does not get the attention it deserves. Most people report that they feel better in terms of energy levels when getting, say, 7 or 8 hours of sleep a night, compared to getting less 6. And on top of this there is the evidence which links short sleep duration with an increased risk of conditions such as cardiovascular disease (e.g. heart disease) and type 2 diabetes.
One such study was published in the journal Sleep Medicine [1]. In this study, 276 individuals aged 21 to 64 were assessed for an average of 6 years each. Compared to those sleeping 7-8 hours a night, those sleeping 6 hours of less were 2.78 times more likely to develop type 2 diabetes. Of course, this does not mean that lack of sleep causes diabetes (only that these two things are associated). However, other evidence shows that inducing sleep deprivation in healthy individuals can also induce insulin resistance (a precursor of type 2 diabetes), and quickly too. This line of evidence suggests that shorter sleep duration may indeed cause type 2 diabetes through some metabolic effect.
This latest study also found that longer sleep duration was also associated with an increased risk of diabetes: individuals sleeping 9 or more hours each night, were about 2.5 times more likely to develop diabetes compared to those sleeping 7-8 hours a night. The findings from this study remained significant after other ‘confounding’ factors (such as BMI and waist circumference) were taken into account.
These findings (increased risk of diabetes with both short and long sleep), mirror the results of a previous study from the same lead author [2]. I have previously written about this study here.
One point I made in this previous post is that, as with shorter sleep duration, we don’t know that longer sleep duration actually causes type 2 diabetes. It might be, that individuals at risk of type 2 diabetes are less healthy and need to sleep more, for instance. We’re unlikely to get much further insight regarding any causal relationship here, because it’s not very practical to make people sleep more to assess what effect this has metabolically.
I have my doubts about what relevance this has anyway, on the basis that not sleeping enough seems to be way more prevalent than sleeping ‘too much’. Plus, there is evidence that sleep duration is generally declining in industrialised countries. In a report of the study that is the focus of the blog that can be read here, I read that, fewer and fewer people sleep the optimum number of hours. A survey conducted in 1960 showed that American adults slept an average of 8 to 8.9 hours a night. By 1995, that average had dropped to 7 hours. A study conducted in 2004 by the National Center for Health Statistics found that one-third of adults aged 30 to 64 slept less than 6 hours a night.
Previously, I have also written about a study which linked short sleep duration with an increased risk of death, particularly from cardiovascular disease.
I think there’s more than enough evidence to suggest that sleep is something to be valued and protected. Yet, for whatever a multitude of reasons, sleep can easily slip down our list of priorities. Coupled with this, is the fact that there does not appear to be any political or commercial appetite for the promotion and popularisation of the potential benefits for sleep. After all, however long we sleep for, we only need to invest in one bed, and while we’re asleep we’re not contributing to the economy.
References:
1. Chaput JP, et al. Sleep duration as a risk factor for the development of type 2 diabetes or impaired glucose tolerance: Analyses of the Quebec Family Study. Sleep Med. 2009 Mar 28. [Epub ahead of print]
2. Chaput JP, et al. Association of sleep duration with type 2 diabetes and impaired glucose tolerance. Diabetologia. 2007;50(11):2298-304.
