Sleep, sugar, and adult diabetes

Diabetes is a disease that, at first glance, seems like a paradox: if glucose is an important source of energy for the body, having high levels of it in the blood that circulates to feed cells from the tips of your toes to the roots of your hair should be an advantage, right?

Wrong. The problem with diabetes is not the high amount of glucose in the blood, but what causes it to remain high: the body's difficulty in removing glucose from the blood and transporting it into the cells, where it is used as energy.

Capturing glucose from the blood requires the hormone insulin: if it is not produced in sufficient quantities, or if the cells do not respond to it—because they have become “tolerant,” for example—they are left without glucose and suffer from starvation, despite all the circulating glucose. High blood glucose levels are only a consequence; their cause is the fact that glucose cannot get where it should be: inside the cells. The resulting health problems are a consequence of cellular starvation.

What does the brain have to do with it? Surprisingly, a study from the University of Chicago recently showed that sleep, or more precisely the dreamless phase of sleep, is critical for regulating the body's glucose metabolism. The team had already shown that adult-onset diabetes, associated with insulin tolerance, is more common among people who have sleep problems or insomnia, and that sleep deprivation in general leads to insulin tolerance.

The team now shows that spending three consecutive nights specifically without the dreamless sleep phase, even with the same total amount of sleep, is enough for young, lean, healthy volunteers to experience a 25% reduction in their insulin sensitivity, and therefore have a reduced ability to use blood glucose—a reduction equivalent to that caused by gaining 8 to 13 kilograms of weight and that found in elderly or obese patients at high risk of developing adult diabetes.

The study raises an intriguing possibility: the high incidence of adult diabetes in the elderly and obese may be related to sleep disorders, which are common in these people, or at least be accentuated in them by lack of sleep.

It will take some time before this possibility is examined. But in the meantime, isn't taking care of glucose distribution to your body's cells a great reason to get plenty of sleep, every night?

Excerpt from Suzana Herculano-Houzel (2025) Neuroscience of Everyday Life, originally published in Folha de São Paulo in January 2008