This is not a new topic. My interest was piqued though after I was writing about sleep apnea affects on surgery. Obese people are found to have sleep apnea issues. But is this a chicken and egg issue? Did being overweight cause sleep apnea? Or did poor sleep cause weight gain?
When googling the medical studies, I found a bunch of studies from 2011-2013. : “Role of Sleep and Sleep Loss in Hormonal Release and Metabolism” was a 2010 Endocrine Development Journal study. It was a comprehensive study focused on the obesity epidemic and diabetes and wondering if sleep issues are a factor in weight gain. The NY Times published an article citing a bunch of studies, “How Sleep Loss Adds to Weight Gain.” LINK.
So to start, you need to know some medical stuff.
First, what hormones are the players?
- Growth Hormone
- GH is a hormone essentially controlled by sleep-wake homeostasis. In men there is a pulse of GH shortly after sleep onset, during slow wave sleep. When the sleep period is displaced, the major GH pulse also shifts, and GH release during sleep deprivation is minimal or absent.
- Cortisol
- Cortisol levels change throughout the day: early morning maximum, decline throughout the day, low in the evening, and an abrupt circadian rise during the later part of the night. Awakenings (during and at the end of sleep) cause a pulse in cortisol secretion. The cortisol rhythm is primarily controlled by circadian rhythm.
- Evening cortisol levels were highest when the subjects were in a state of sleep debt.
- Cortisol levels being higher = BAD. Not only do you crave food, but you crave food that is not good for you. “A sleepy brain appears to not only respond more strongly to junk food, but also has less ability to rein that impulse in.”
- Adenosine.
- Adenosine is a metabolic byproduct that disrupts neural function (your ability to think clearly) and promotes sleepiness as it accumulates in the brain.
- Caffeine stimulates by blocking adenosine.
- Adenosine is cleared when we sleep.
- Without enough rest, adenosine builds up. This may lead to poor brain communication, hence the choice of junk food instead of good food.
- Leptin
- Is the satiety hormone made by fat cells.
- Leptin levels are dependent on meal intake – lowest in the morning and increasing levels throughout the day, with the maximum at night. Leptin is elevated during sleep, likely to inhibit hunger while you sleep.
- Leptin levels were lowest when the subjects were in a state of sleep debt. No leptin = not sated = HUNGRY.
- Ghrelin
- A hunger hormone released primarily from stomach cells. Ghrelin levels decrease rapidly after meal ingestion and then increase in anticipation of the following meal. Ghrelin levels decrease as you sleep.
- Ghrelin was assayed and showed a 28% increase after sleep deprivation. Higher Ghrelin = HUNGRY.
- Ghrelin/Leptin ratio
- One study showed the effects of longer sleep. Questionnaires on hunger and appetite were completed and indicated a 24% increase in hunger and a 23% increase in global appetite after 4 hour sleep nights vs. 10 hour nights.
- Appetite for high carbohydrate nutrients was the most affected, with a 32% increase.
- People reported feeling increased hunger which correlated with the increase in ghrelin to leptin ratio (i.e. hunger factor/satiety factor)
- Both groups ate more calories when unlimited food presented, but the lower sleep people ate more snacks, not the good food.
- One study showed the effects of longer sleep. Questionnaires on hunger and appetite were completed and indicated a 24% increase in hunger and a 23% increase in global appetite after 4 hour sleep nights vs. 10 hour nights.
- Glucose tolerance
- Cerebral glucose utilization represents 50% of total body glucose disposal during fasting conditions and 20–30% postprandially.
- There is decreased glucose use during the first part of the night’s sleep.
- Glucose tolerance was decreased by more than 40% when the subjects were in the state of sleep debt.
- A study showed reduced sleep quality, without change in sleep duration, has adverse effects on glucose metabolism
- Insulin
- Several studies have shown recurrent partial sleep restriction or experimentally reduced sleep quality results in insulin resistance, another risk factor for weight gain and obesity. Because this decrease in insulin sensitivity was not associated with increased insulin release, diabetes risk was elevated.
Sleep has two basic phases: non REM (rapid eye movement) sleep and REM sleep.
- Non REM sleep has slow waves on your EEG. In deeper sleep, the waves are more regular and have higher amplitude waves.
- REM sleep is the best sleep. The length of REM sleep cycle goes up as you cycle longer into the night.
- During REM sleep your brain is more active and burns more calories.
- A study in children showed BMI was statistically related to total sleep time, sleep efficiency , and REM density.
- “Compared with normal-weight children, overweight children slept about 22 minutes less and had lower sleep efficiency, shorter REM sleep, lower REM activity and density, and longer latency to the first REM period”.
- When adjusted for other parameters,
- 1 hour less of total sleep was associated with approximately 2x risk of being overweight,
- 1 hour less of REM sleep was associated with about 3x risk of overweight
- REM density and activity below the median increased the odds of overweight by 2x – 3x.
How long should you sleep? And does this cause obesity?
- American adults sleep on average 6 h 40 min during weekdays and 7 h 25 min during the weekend.
- In contrast, in 1960, the average sleep duration was 8.5 h This shows a reduction in sleep of 1.5-2 hours has occurred.
- Adolescents should sleep 9-10 hours. Studies show they average 7 hours.
- In adults, as of May 2009, a total of 29 cross-sectional studies and 6 prospective studies originating from a wide variety of industrialized countries have been published. Thirty of these 35 studies had positive findings. Obesity risk generally increased for sleep durations under 6 h.
- Associations between short sleep and diabetes have been made.
My thoughts?
I think we as physicians need to look at all factors affecting patients. Many of my patients come in fighting weight gain and menopause. (Is it related –in menopause we have weight gain and poor sleep? Chicken and egg scenario? Did poor sleep in menopause cause the weight gain in menopause? Or did our weight gain cause poor sleep?) We need to discuss things like sleeping and diet when we discuss surgeries, medical conditions, and weight loss. There is a lot of interconnection.
One doctor said sleep is like “rebooting” the brain. I like this analogy. Just like your computer and phone, we need to reboot. There are things you can do for simple sleep hygiene: no screens before bed, no distracting things in your bedroom, no caffeine after 2 pm.
If you don’t sleep well, sleep deprivation raises cortisol, adenosine, and ghrelin. It makes you resistant to insulin. It lowers leptin. You have less REM sleep. The most important sleep is that last sleep of the night. Don’t set your snooze alarm–try to get your hours in uniterrupted. One sleep expert I read said the toll of poor sleeping is 2 pounds a year. In the studies above, they found obesity risk increased for sleep durations under six hours.