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In our articles on wearables and insurance products we highlight that some insurers, in addition to the step count measured by a wearable device, also use sleep duration as one of their criteria for policyholders to gain premium discounts.

Sleep plays a vital role in mental and physical well-being, quality of life and safety. Sleep helps the brain to function correctly and during sleep the brain prepares for the following day. A good night’s sleep aids the ability to learn and concentrate, while not enough sleep can affect later brain activity leading to reduced creativity and decision-making. Sleep deficiency can lead to depression and suicide.

It also has an important role in physical health, with deficiency being linked with increased cardiovascular disease and, when hormonal balance is affected, an increased risk of diabetes. There is of course an increased accident risk for those driving or operating machinery.

There is an increasing body of evidence to suggest that either too little or too much sleep are associated with poor health outcomes including overall mortality, cardiovascular disease, diabetes, respiratory disease and hypertension. The relationship between duration of sleep and overall mortality is generally seen as being U-shaped. Generally, sleeping between six and eight hours per night is seen as being optimal; sleeping more than nine hours per night is seen as an indicator of some sort of co-morbidity, whether diagnosed or not; and sleeping less than five hours is a marker of increased all-cause mortality.

However, other studies suggest that there may not be a robust evidence base for this conclusion and that some of the research has had some sort of bias or confounding factors that were in play.

Some fitness trackers include sleep monitoring in their basic functionality. For example, a Fitbit detects sleep based on movement – or, more precisely, lack of movement. It records the amount of time that you sleep and estimates ‘sleep efficiency’ which incorporates time taken to fall asleep and time restless. The Vivosmart HR device too tracks sleep and gives a breakdown of light sleep and deep sleep together with how many times you were awake and for how long.

Given that some insurers include sleep duration in their ‘health’ tracking, the obvious question to ask is how accurate are fitness trackers in measuring sleep. As you might expect the jury is out and we found a variety of expert opinion that doubted their accuracy. On the other hand, there are one or two studies out there which suggest the accuracy is reasonably good.

Evaluation of a consumer fitness tracking device to assess sleep in adults. de Zambotti M, Claudatos S, Inkelis S, Colrain IM, Baker FC. Chronobiol Int 2015;32(7):1024-1028

Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies. Cappuccio FP, D’Elia L, Strazzullo P, Miller MA. Sleep 2010;33(5):585–592

Sleep duration and all-cause mortality; a critical review of measurement and associations. Kurina LM, McClintock MK, Chen J-H, Waite LJ, Thisted RA, Lauderdale DS. Ann Epidemiol 2013;23(6):361–370

Sleep duration and mortality: a systematic review and meta-analysis. Gallicchio L, Kalesan B. J Sleep Res 2009;18(2):148-58