Cardiovascular risks
Reduced sleep is also related to an increase in both cardiovascular events and cardiovascular disease. In the Nurses' Health Study, researchers found evidence of increased risk of coronary events in female subjects who obtained seven hours or less of sleep per night compared to those who averaged eight hours per night. In another study, a two- or three-fold increase in risk of cardiovascular events, such as stroke or myocardial infarction, was found in subjects with an average sleep duration of five hours or less per night (or chronically having five hours or less of sleep per night at least twice per week) was reported. Similar findings have been observed in studies examining cardiovascular health in shift workers, who typically experience disruptions in their circadian rhythm. Although certain of a link between short sleep and cardiovascular risk, researchers do not understand the reason for this.
Cancer
In a prospective study of 23,995 Japanese women, shorter sleep duration, specifically six hours or less per night, was associated with a higher risk of breast cancer when compared with women who slept seven hours per night. Researchers suggested that melatonin, which is secreted mainly from the pineal gland, is the key factor in this link between sleep and cancer. Shorter sleep results in a shorter duration of nocturnal melatonin secretion and lower melatonin levels have been associated with an increased risk of breast cancer.
Obesity
Increasingly, scientists hypothesize that sleep deficits cause obesity. According to the authors of a study of 1,024 volunteers from the Wisconsin Sleep Cohort Study — a population-based longitudinal study of sleep disorders — too little sleep apparently alters your body's regulation of appetite-regulating hormones. Participants underwent nocturnal polysomnography and reported on their sleep habits through questionnaires and sleep diaries. In addition, each morning they gave blood samples, which were evaluated for serum leptin, ghrelin, adiponectin, insulin, glucose, and lipid profile.
After sorting through these measures as well as sleep habits and body mass index (BMI) for each of the participants, researchers identified a relationship between sleep duration and BMI. Increased BMI was proportional to decreased sleep duration for those participants who slept eight hours or less (74.4 percent of the sample) each night. Independent of BMI, short sleep patterns were also associated with low leptin and high ghrelin. Since reduced leptin and elevated ghrelin increase appetite, this likely explains the increase in BMI.
Sources: Basner M, Dinges DF. Dubious Bargain: Trading Sleep for Leno and Letterman. Sleep. 2009.