From Heart to Hormones: The Far-Reaching Effects of Sleep

Sleep affects multiple physiological systems; however, a comprehensive overview has not yet been reported.

A study published in Nature Medicine analyzed sleep characteristics in adults and their associations between sleep traits and body characteristics across 16 body systems.

Researchers led by Eran Segal, PhD, from the Department of Computer Science and Applied Mathematics, Weizmann Institute of Science, Rehovot, Israel, analyzed sleep data from the Human Phenotype Project, a longitudinal study that collects extensive clinical and molecular data from healthy individuals aged 4src-7src years in the general Israeli population.

The study analyzed data for 448 sleep characteristics collected from 16,812 nights of home sleep apnea test monitoring in 6366 adults (2.42 nights per individual on average) using wearable sensors. These sensors track breathing, snoring, sleep position, sleep phases, and heart rates. Of the participants, 47.8% were men, with an average age of 52.4 years and an average body mass index of 26.1. Additionally, 574 participants were monitored twice, 2 years apart, to assess changes in sleep parameters over time.

Sleep and Age

The analysis showed that sleep patterns changed with age. Every year, deep sleep decreased by src.13%-src.14%, and light sleep increased by src.18%-src.23%. The peripheral apnea-hypopnea index (pAHI) increased significantly with age, and the results were consistent with those of previous studies. By age 4src, 1src% of men develop obstructive sleep apnea, while women exceed this threshold at age 55, most likely linked to the onset of menopause.

Certain sleep parameters, such as snoring and oxygen saturation, remained relatively stable. However, sleep patterns and pAHI showed measurable changes over time. On average, deep sleep accounts for just under 18% of total sleep time, with similar percentages observed in both men and women, and the average sleep duration is approximately 6 hours per night.

Sleep and Lifestyle

The study analyzed 25,164 correlations and identified over 12,4srcsrc significant ones. The strongest associations were observed between pAHI and body characteristics, particularly visceral adipose tissue, blood triglyceride levels, and bone density in the rib area. In terms of lifestyle factors, pAHI was associated with television use and smoking habits. Heart rate variability during sleep was linked to sex, frailty, and bone density.

Beyond individual parameters, this study examined how the sleep system relates to 16 other physiological systems, including kidney function, immune response, microbiome composition, and mental health. The study also included lifestyle factors such as medication use, diet, and lifestyle.

The findings revealed that sleep measures, when considered collectively, are stronger predictors of insulin resistance and blood lipid levels than measures from any other body system. However, sleep itself does not directly predict visceral adipose tissue levels, suggesting that visceral fat is unlikely to mediate the association between sleep and insulin resistance.

Conversely, among the body systems examined, lifestyle was the strongest predictor of sleep quality, outweighing age, body mass index, and visceral fat. Other key contributors to sleep parameters included the cardiovascular system, insulin resistance, hematopoietic function, lipid metabolism, and psychological health.

Sleep and Disease

Sleep parameters are associated with various diseases; however, the correlations differ between men and women. In women, sleep is linked to hypertension, osteopenia, and prediabetes, whereas in men, it is more strongly associated with allergies and back pain. Heart rate variability during sleep is associated with hypertension, atopic dermatitis, and hearing loss in men, whereas in women, it is more closely linked to asthma, osteoporosis, and anxiety.

Overall, sleep structure, including duration and percentage of deep sleep, appears to be more strongly related to endocrine conditions, whereas pAHI is a stronger predictor of cardiovascular and metabolic diseases.

However, some commonly proposed associations were found to be weak or absent. For example, liver health and kidney function are poorly associated with sleep duration. Additionally, previous hypotheses regarding the impact of diet and microbiomes on individual sleep characteristics appear to be limited. However, microbiome metabolism was strongly associated with obstructive sleep apnea in both sexes, whereas diet was correlated with obstructive sleep apnea only in women.

Data

Speaking with Univadis Italy, a Medscape Network platform, sleep researcher Ugo Faraguna, MD, PhD, associate professor of physiology at the University of Pisa in Pisa, Italy, said that “the study offers interesting insights and suggests that sleep parameters could be key determinants of health, potentially influencing various physiological functions.”

“This study confirms several previously known associations between sleep and other physiological parameters. Its novelty lies in the extensive data collected in the home setting. These data allowed researchers to classify the most relevant associations and compare them directly, offering a more comprehensive and holistic perspective than that of previous studies. Among these associations, the strongest link was found between sleep-related breathing disorders and body composition, particularly visceral adipose tissue; in contrast, the associations between sleep and renal function, nutrition, and microbiota were relatively weaker than expected,” he added.

Giorgio Gilestro, PhD, a reader in systems neurobiology at Imperial College London, London, England, specializing in sleep biology and neurobiology, noted that while “the study is valuable due to the large number of subjects in the cohort examined, but it is not particularly innovative from a scientific point of view because it mainly confirms existing knowledge rather than introducing new findings.”

The primary confirmation is that obesity, particularly visceral fat, is the strongest factor associated with sleep apnea.

“It has been known for decades that the best way to combat sleep apnea is weight loss,” said Gilestro.

“Second, it is yet another large-scale study that disproves the myth that we all need to sleep 8 hours a night. However, biology does not function in this manner. It would be like assuming we all need to wear the same shoe size,” Gilestro explained.

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