Hormones and sleep: A two-way street
A hormone is a chemical released by a cell or gland in one part of the body that subsequently affects cells in another part of the body. In essence, hormones are chemical messengers, traveling in your bloodstream to tissues or organs. They are involved in many different bodily processes, including metabolism, growth and development, reproduction, sexual function and mood.
There is a close link between sleep and hormones. A clear demonstration of this is when women become pregnant. Pregnancy is associated with alterations to reproductive hormones, estrogen and progesterone, which typically rise throughout pregnancy and peak at term. This increase may initially be associated with elevated sleepiness in the mother, often resulting in an increase in total sleep time and daytime napping . The distribution of sleep stages, deep sleep and REM sleep, may also be altered at this time. Developing physical changes in the latter stages of pregnancy (third trimester) have also been proposed to disturb sleep in the majority of women. Similarly, during the menopause, sleep disturbance and insomnia symptoms are very common, and have been linked to decreased levels of estrogen and associated hot flashes.
Specific sleep stages may also be related to certain hormonal release. For example, it has been well documented that during deep sleep there is an increase in the release of human growth hormone, which stimulates cell reproduction and regeneration. Interestingly, a recent study by Lampl & Johnson (2011) found that infant growth spurts were associated with increased and more consolidated sleep, and the mechanism thought to explain this relates to increased deep (slow-wave) sleep and the associated increase in growth hormone.
Finally, sleep loss and sleep disturbance have also been shown to negatively impact on hormonal balance. For example, the appetite-suppressing hormone, leptin, has been found to be decreased after several nights of sleep restriction. Similarly, the appetite-stimulating hormone, ghrelin, has been found to be increased after sleep restriction. Alterations to these two hormones due to sleep loss may, therefore, encourage people to seek out extra calories!
Lampl, M., Johnson, M.L. (2011). Infant growth in length follows prolonged sleep and increased naps. SLEEP, 34(5), 641-650.