Sleep is one of the most undervalued essential practices in modern society. In 1910, an average night’s sleep was 9 hours. By 1975, it was down to 7.5 hours. From 2000 to 2002, polls found that it had fallen to 6.9 hours. Today, many people average just 5-6 hours of sleep per night.
At the same time, obesity rates have doubled! Sleep and the neuroendocrine system are intricately entwined. Chronic lack of sleep is thought to be linked to diabetes, hypertension, obesity and memory loss. Lack of sleep increases blood pressure and the risk of heart disease.
A recent study by the University of Chicago found that cutting sleep from 8 hours to 4 hours a night for less than one week produced physiological changes that resembled the effects of advanced aging and early diabetes.
Those changes happened in less than one week!
The study’s participants took 40% longer to regulate their blood-sugar levels after eating and their ability to secrete insulin and respond to it decreased by 30%.
Lack of sleep affects the secretion of thyroid-stimulating hormone and increased levels of the “stress hormone,” cortisol.
The study found that recovery occurred and above-average functioning occurred when the subjects slept more than 8 hours a night.
Lack of Sleep Means Lack of Weight Loss
So how does sleep affect weight?
Sleep affects the release of hormones by the hypothalamic-pituitary axes (HPA) and the autonomic nervous system (ANS). Sleep triggers or inhibits the production or release of various hormones.
Growth hormone is affected by sleep. You can work out for hours, but if you don’t get enough sleep your body is not going to turn fat into muscle.
Lack of sleep raises the level of cortisol which triggers the fight-or-flight response. During stress, our body shuts down normal maintenance. It activates fat storage and releases lots of sugar (for instant energy) into the bloodstream. It depletes the body of nutrients and triggers cravings for simple carbohydrates and sugar. Chronic stress promotes insulin resistance.
Leptin and ghrelin are two very important appetite-controlling hormones that are linked to sleep. Leptin suppresses appetite and ghrelin increases it. When people are subjected to sleep loss, leptin levels fall and ghrelin levels rise. Even when they received plenty of nutrition, people that didn’t get adequate sleep were compelled to eat more. Because leptin levels were low, their brains just didn’t get the message that they were satiated—instead they just kept getting the message: “Hungry! Eat!” When deprived of sleep, study participant’s desire for high-carbohydrate and calorie-dense foods increased by 45%.
A joint study conducted by Stanford University and the University of Wisconsin measured leptin and ghrelin levels, body fat and sleep amounts in 1000 people. They found that those who slept less than 8 hours a night had low leptin levels, high ghrelin levels and higher levels of body fat. The participants that slept the fewest hours a night weighed the most.
Another study, presented at the 2006 American Thoracic Society International Conference, came up with some confounding information. 70,000 middle-aged women were studied for 16 years.
The study found that:
- Women who sleep 5 hours or less weigh more than those that sleep 7 hours.
- Women who sleep 5 hours per night are 32% more likely to experience weight gain of 33 pounds or more and 15% more likely to become obese than those that sleep 7 hours.
- Women that sleep 6 hours a night are 12% more likely to gain 33 pounds or more and 6% more likely to become obese than those that sleep 7 hours.
What was confounding in this particular study is the fact that the women that slept less did not eat more.
“Prior studies have shown that after just a few days of sleep restriction, the hormones that control appetite cause people to become hungrier, so we thought that women who slept less might eat more,” says the study’s leader, Sanjay Patel. “But, in fact, they ate less. That suggests that appetite and diet are not accounting for the weight gain in women who sleep less.”
So even though leptin and ghrelin levels might affect appetite, it is more likely that the hormones that affect the metabolism of glucose and insulin-response are behind weight gain during sleep deprivation.
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