Why might afternoon nappers be at greater risk of diabetes?

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I noticed a few reports last week (an example here) regarding a study that was presented at a diabetes conference. Apparently, the research shows that individuals taking naps in the afternoon is associated with a significantly enhanced risk of developing diabetes. When such studies are reported there’s a tendency for journalists (and sometimes the originators of the study) to suggest that because two things are associated, one is causing the other. For example, the headline of the BBC report I linked to above reads: Napping ‘increases diabetes risk’.

However, just because two things are associated most certainly does not mean that one is causing the other. It might be that before individuals develop full-blown diabetes they are prone to fatigue and sleepiness as a result of a pre-diabetic state. In this way, it might be the pre-diabetic state, not the napping, that leads onto actual diabetes.

While there is no relevant science in this area that I am aware of, there is I think a quite precise mechanism that might explain the link between afternoon napping and increased risk of diabetes. It concerns fluctuations in the level of sugar in the bloodstream.

After eating, blood sugar levels usually rise, which in health causes the body to secrete a hormone call insulin, one of the chief effects of which is to reduce blood sugar levels. However, if for any reason the rise is blood sugar level is substantial, insulin secretion can follow suit, and this can lead to low blood sugar (hypoglycaemia) some time later.

Hypoglycaemia will generally cause physical and mental energies to stall, and may induce sleepiness to the extent that someone actually feels compelled to sleep. One of the other symptoms that this can give rise to is the feeling of peckishness (particularly for something sweet) on awakening.

The most common time in the day for this effect to occur is the mid-late afternoon (about 3 hours after lunch). I reckon the mid-late afternoon lull that some of us suffer from is quite often related to this specific imbalance. For a lot of us, it reflects the body’s reaction to what a lot of us choose to eat a lunch (something bread-based).

Now, if an individual habitually has this imbalance, the likelihood is that they’re going to be secreting relatively high levels of insulin too. As a result, one or both of two things can happen in time:

1. the body may become somewhat ‘numb’ to the effects of insulin

2. the pancreas which secretes insulin can exhaust, leading to inadequate amounts of insulin

Either of these states can lead an individual down a path to type 2 diabetes. And these mechanisms may possibly explain why individuals taking afternoon naps are more prone to developing diabetes in time.

It has also been suggested that the need to nap during the afternoon is a sign of some form of sleep disturbance that could be increasing diabetes risk. Here again, though, blood sugar imbalance may be playing a part.

The reason is that just like blood sugar levels can fall in the mid-late afternoon, they can fall in the middle of the night too (often at 3.00-4.00 am). In response to this, the body is likely to secrete certain hormones that will liberate sugar from stores fuels such as glycogen in the liver. This will certainly get the body out of a hole, but the problem is the hormones that the body secretes in response to low blood sugar include adrenaline and cortisol: the two major ‘stress hormones’. Their presence in the system will do nothing to promote deep sleep, and may trip individuals into wakefulness. Individuals may find it difficult to drop off again, which could mean that they really don’t get enough sleep. The ‘sleep debt’ so incurred could easily manifest in the form of afternoon fatigue. Cortisol, as it happens, also antagonises the effects of insulin, which is another mechanism by which blood sugar imbalance may increase diabetes risk.

We don’t know if these theories are relevant or not. But one thing I do know for sure is this: when individual take steps to stabilise their blood sugar levels, they usually are much more alert and productive in the afternoons, and much less likely to wake up at night. For most individuals, blood sugar stability can be achieved by eating a diet based on natural unprocessed ‘primal’ foods (such as meat, fish, eggs, nuts, seeds, fruits and vegetables other than the potato), and by eating such foods regularly.

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