Sleep and Metabolism
A very strong and complex relationship exists between sleep and our body’s metabolism. The intricacies of the association between sleep and metabolism are only beginning to emerge. The major question that we shall address in this article is “How does sleep (and the lack of sleep) affect metabolism?” Since it is nearly impossible to describe the effects of sleep on all aspects of metabolism, we shall touch upon salient points such as the metabolic rate, glucose metabolism, etc…
To begin with, let’s examine how our body’s metabolic rate is influenced by sleep. Scientists have confirmed that a person’s metabolic rate drops by an average of fifteen percent when he switches from a peaceful, wakefulness state into normal sleep. Thus, to fall asleep acts to reduce our metabolic rate. By sleeping, we burn less number of calories, and so, manage to save a small amount of energy as compared to when we are awake. However, this sort of relationship between sleep and metabolism has been elucidated long back.
More recently, scientists have tried to focus on more specific areas. In a series of studies carried out at the University of Chicago Medical Centre, it became clear that chronic sleep deprivation adversely affected key metabolic processes in our body such as carbohydrate metabolism and regulation of hormonal secretion.
Strikingly, chronically sleep deprived study subjects exhibited significantly impaired glucose regulation. In the typical sleep deprived individual, the ability of the body to secrete insulin fell by a drastic thirty percent. In the same study, the researchers found out that it took forty percent longer time for the sleep deprived person’s body to control their blood glucose levels following an injection of glucose. Almost all of the measurements carried out on sleep starved subjects, indicated that their blood values closely resembled those of diabetic patients at the onset of their disease.
Several previous studies have documented that people suffering from lack of sleep over extended periods of time, tend to eat more. Biochemical studies have revealed that a hormone called leptin is involved. Sleep deprivation causes fat cells in our body to secrete lower amounts of leptin. Our body responds to lower leptin levels by inducing a hunger craving, especially toward more carbohydrate-rich foods.
Two other, important hormones that are affected by sleep starvation are thyroid stimulating hormone and cortisol. In the study mentioned above, subjects who were allowed to sleep for only four hours a night (the recommended number being eight) for six consecutive nights had reduced levels of thyroid stimulating hormone. However, in the same study subjects, levels of the hormone, cortisol, increased steadily during evenings.
So what do these altered hormone levels and carbohydrate metabolism mean? Higher levels of cortisol in the evenings and diabetes are both conditions that are considered as hallmarks of aging. To sum up, chronic sleep deprivation alters the metabolism so that the metabolic profile of such a sleep starved person looks similar to that metabolic profile of an aged person! In effect, going by the present knowledge, it seems that chronic sleep deficit results in accelerated aging.
When the subjects of the sleep deprivation study reverted back to their original eight hourly sleep patterns, their metabolic measurements also came back to their initial, normal values. It therefore seems that the negative effects of sleep deprivation on metabolism over reasonable amounts of time (such as for a week or so) can be overcome by regaining normal sleep periods. But clearly, long term sleep deprivation has a negative impact on our metabolism.