How might sleep duration influence the risk of metabolic syndrome?
We already know that too little sleep can impact our health in myriad ways, but to what extent does too much sleep effect our well-being?
A study recently conducted by researchers from Seoul National University College of Medicine in South Korea has discovered that both of these extremes are liable to increase the risk of metabolic syndrome.
Lead study author Claire E. Kim and her team analyzed data sourced through the Health Examinees (HEXA) study, a large population study investigating the interaction of genetic and environmental factors in the context of chronic disease incidence in South Korea.
Their results — which have been reported in the journal BMC Public Health — not only indicate a correlation between extremes of sleep and metabolic syndrome, but also suggest that the risks may be different depending on a person's sex.
Sleep duration and metabolic syndrome
Kim and team analyzed the medical data of 133,608 men and women aged 40–69. The participants also self-reported how much sleep they got every day, including both night-time sleep and any daytime naps.
The HEXA study included information on the participants' medical histories, use of medication, modifying lifestyle factors, and family medical history.
All of the volunteers also provided samples of plasma, serum, blood cells, urine, and chromosomal DNA, among other things.
Analyses of the participants' collected data — including the self-reported information on sleep hygiene — revealed that both fewer than 6 and more than 10 hours of sleep on a daily basis were linked to the presence of metabolic syndrome.
Individuals were deemed to have metabolic syndrome if they presented at least three of these tell-tale symptoms: excess fat around the waist; high triglyceride levels; low levels of high-density lipoprotein (HDL), or "good," cholesterol; high fasting blood glucose; and hypertension.
Just over 29 percent of the male participants had metabolic syndrome, and 24.5 percent of the women showed signs of this condition. The team noted certain differences in risk patterns.
'Potential gender difference' observed
So, women who slept little — for fewer than 6 hours per day — were likelier to have a higher waist circumference, indicative of excessive belly fat, than women who slept for 6–7 hours per day.
Men who slept for under 6 hours were more likely to have not just a higher waist circumference, but also metabolic syndrome.
As for oversleeping — defined as more than 10 hours of sleep each day — it was tied to raised triglyceride levels, as well as metabolic syndrome, in men.
But in women, it was linked with even more negative health outcomes: not just metabolic syndrome and high triglyceride levels, but also high blood sugar, low HDL cholesterol, and higher waist circumference.
Of the participants, about 13 percent of the women and 11 percent of the men slept too little, and 1.7 percent of the women and 1.5 percent of the men slept for over 10 hours every day.
"This is the largest study examining a dose-response association between sleep duration and metabolic syndrome and its components separately for men and women," Kim explains.
"We observed a potential gender difference between sleep duration and metabolic syndrome, with an association between metabolic syndrome and long sleep in women and metabolic syndrome and short sleep in men."
Claire E. Kim
It is not clear how sleep patterns might influence the development of metabolic syndrome, but the researchers note that sleep duration could impact the production of key hormones that regulate appetite and how much energy our bodies produce and consume.
Kim and colleagues also note that, although this study's findings may be compelling, the research observed an association that may not necessarily speak of a cause and effect relationship.
The authors acknowledge some limitations to their study, including the fact that the information on sleep duration was self-reported, so there were no objective measurements in this regard, as well as the fact that the analysis amalgamated night-time sleep and daytime naps.