It may come as no surprise that hormonal upheaval 鈥� say, during puberty or menopause 鈥� can play havoc with sleep. But our hormones influence sleep all the time, not just during big changes. What鈥檚 more, we are starting to see that this relationship goes both ways: as much as our hormones affect how we sleep, how we sleep influences our hormones.
A better understanding of this relationship could improve both our sleep and our general health. But, like a lot of relationships, it is complicated.
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This article is part of special series investigating key questions about sleep. Read more here.
There are two basic processes that regulate sleep. The first, known as process S, keeps track of how long we have been awake through the build-up of the , a by-product of cellular metabolism. Once enough has accumulated, like sand piling up at the bottom of an hourglass, the pressure to nod off becomes difficult to resist. The second, called process C, is driven by our circadian system, the rhythms of activity in almost all our cells timed to Earth鈥檚 24-hour cycle of day and night.
Process C, which is largely regulated by exposure to light, manages this through the release of two key hormones, and cortisol. Produced by the pineal gland during the dark hours, melatonin tells the parts of the brain that control sleep that it is night, so we fall asleep at the appropriate time. Cortisol picks up where melatonin leaves off, spiking in the morning and boosting our alertness to rouse us out of bed.
Hormones change all the time
Production of these hormones changes throughout our lives. During puberty, , although it is unclear what role this might play in the natural shift in circadian rhythm that many teenagers experience that has them falling asleep . Cortisol levels can increase with age, which may impact sleep quality and has been associated with a decline in rapid eye movement sleep. For women, , the relationship between hormones and sleep is even more complex. For example, decreasing concentrations of melatonin post menopause may be related to difficulty falling or staying asleep and, although the mechanisms aren鈥檛 yet fully understood, higher levels of follicle-stimulating hormone, which occur during part of the menstrual cycle, for instance, appear to .
Over the past decade or so, however, it has become apparent that hormones and sleep have a two-way relationship; it isn鈥檛 just that hormones control sleep, but poor sleep can also interfere with our hormones in surprising ways.
鈥淗ow the body processes, metabolises and releases various hormones can be disrupted by a lack of sleep,鈥� says , director of the Center of Excellence for Sleep & Circadian Research at Columbia University in New York. For instance, people who experience poor sleep also tend to be , which is released during deep, or 鈥渟low wave鈥�, sleep. It promotes growth in children and regulates metabolism and supports cellular repair in adults. Studies have also , where the thyroid gland doesn鈥檛 produce enough of the hormones thyroxin, triiodothyronine and calcitonin, resulting in fatigue and weight gain.
How sleep helps manage weight
An underactive thyroid isn鈥檛 the only reason why the consequences of disrupted sleep can be seen in our waistlines. Various studies have suggested that both chronic sleep loss and circadian disruption can affect control of blood sugar levels and how efficiently we digest food, resulting, perhaps unsurprisingly, in a raised risk of obesity and . We are just starting to unpick some hormonal mechanisms behind these changes.
For instance, when St-Onge and her colleagues for four consecutive nights, they observed a rise in the appetite-stimulating hormone ghrelin in the men and a fall in the satiety-promoting hormone glucagon-like peptide 1 in the women. 鈥淎t the end of the day, it means the same thing: people are more motivated to eat more, which can lead to increases in body weight and accompanying metabolic disorders,鈥� says St-Onge.
Disrupted sleep can cause metabolic changes surprisingly quickly. In one study, and his colleagues at the University of Utah had participants . 鈥淚f we measure their insulin sensitivity, which is a risk factor for diabetes, we can see that some people go from perfectly healthy to a pre-diabetic state in three days,鈥� he says. Although the effects were reversible with catch-up sleep, it took six to 10 days for these people to return to baseline.
The good news is that it is possible to improve parts of the relationship between sleep and hormones. Our food choices affect how well we sleep (see 鈥淭he surprising relationship between your microbiome and sleeping well鈥�). Melatonin, for instance, is produced from an amino acid called tryptophan, which we get from protein-rich dietary sources, so eating more of these ensures that tryptophan is available to produce melatonin when night comes. Light also affects melatonin production, which is why dimming the lights and putting down your phone well before bedtime will help.
