There was an interesting, I think, study published this week in which the association between sleep habits and certain metabolic processes were assessed in diabetics and non-diabetics [1]. The study assessed sleep habits by self reports and something known as ‘actigraphy’ (the measuring of sleep through a device worn on the wrist). Health markers assessed included blood sugar levels, insulin levels and extent of ‘insulin resistance’.
Insulin resistance, describes a state where some of the body’s tissues are not responding to insulin, which causes, among other things, generally elevated levels of sugar in the bloodstream. Insulin levels will tend to be high too. Higher levels of insulin may predispose to fat gain. However, if sugar is not making its way efficiently into, say, the muscles and brain, we can end up tired and hungry. In general terms, insulin resistance is not a good thing, and neither is generally elevated levels of sugar and insulin.
In the study in question, in non-diabetics, there was no association found between sleep habits and levels of sugar and insulin and insulin sensitivity.
The situation, however, was very different in diabetics.
Poor sleep in this group was associated with raised levels of blood sugar and insulin. Insulin resistance was significantly greater too. In short, in diabetics, poor sleep habits were associated with worsened blood sugar control and, in all likelihood, enhanced risk of diabetic complications and disease in time.
Now, so-called epidemiological studies of this nature can only tell us that poor sleep and worse health markers are associated. It does not prove that sleeping poorly causes these issues. However, there is other evidence in the scientific literature that supports the idea that sleep problems can actually lead directly to the sort of issues we’re talking about here.
In one study, nine health adults were tested to see what effect sleep deprivation has on insulin resistance [2].
On one night, individuals were allowed to sleep for up to 8.5 hours (23.00 – 7.30 hrs). On another night, sleep was only permitted for four hours (01.00 – 05.00 hrs). The actual average sleep times were 7 hours 34 minutes and 3 hours 46 minutes respectively.
The results show that in the sleep-deprived state there was evidence of insulin resistance. ‘Endogenous’ sugar production (internal production of sugar, say, from the liver) was higher, and clearance of glucose (say, into muscle cells) was lower in the sleep-deprived state.
Now, less than four hours sleep is not much sleep. But then again, increased insulin resistance was seen in individuals after just one night of sleep deprivation. It’s possible that less extreme sleep deprivation over long periods of time also poses hazards for the body. In fact, lower sleep durations has previously been linked with an increased risk of type 2 diabetes.
I don’t know how well any underlying mechanisms here are understood. However, it is known that sleep deprivation can cause increases in the ‘stress’ hormone cortisol. And cortisol is known to have the capacity to induce insulin resistance.
References:
1. Knutson KL, Cross-Sectional Associations Between Measures of Sleep and Markers of Glucose Metabolism Among Subjects With and Without Diabetes: The Coronary Artery Risk Development in Young Adults (CARDIA) Sleep Study. Diabetes Care. 2011;34(5):1171-6.
2. Donga E, et al. A single night of partial sleep deprivation induces insulin resistance in multiple metabolic pathways in healthy subjects. J Clin Endocrinol Metab. 2010;95(6):2963-8
