In a study of the sleeping habits and metabolism of 1,620 people, people who stayed up late, regardless of lifestyle factors, had a higher risk of diabetes or reduced muscle mass than those who were early risers.
The results, published in the journal The Journal of Clinical Endocrinology and Metabolism, came from a survey of middle-aged adults in Korea designed to establish their “morning-ness” versus their “evening-ness.”
The questionnaire established whether the 47- to 59-year-olds were strong morning types, strong evening types, or in the spectrum between - against questions such as how easy they found it to get up in the morning, and how alert they then felt, as well as questions about times of going to bed and sleeping preferences across different scenarios.
Using the morning or evening chronotype, which is described as “a trait determining individual circadian preference in behavioral and biological rhythm relative to external light-dark cycle,” the authors sought to test whether there was a relationship between chronotype and metabolic disorders.
Chronotypes were compared with results for:
- Metabolic syndrome (in which a number of cardiovascular and diabetes risk factors are raised)
- Sarcopenia (reduced muscle mass)
- Visceral obesity (excessive abdominal/belly fat).
All participants underwent:
- The oral glucose tolerance test for diabetes
- Body composition measurement - body fat versus lean mass, as scanned by DEXA (dual-energy X-ray absorptiometry)
- Visceral obesity diagnosis - visceral fat area of more than 100 cm2, as measured by abdominal computed tomography (CT).
Circadian rhythms ‘important to metabolic regulation’
The study concludes: “At the population level, evening chronotype was independently associated with diabetes, metabolic syndrome and sarcopenia. These results support the importance of circadian rhythms in metabolic regulation.”
Commenting on evening-ness being associated with a higher risk of diabetes and reduced muscle mass, one of the study’s authors, Dr. Nan Hee Kim of the Korea University College of Medicine in Ansan, says:
“This could be caused by night owls’ tendency to have poorer sleep quality and to engage in unhealthy behaviors like smoking, late-night eating and a sedentary lifestyle.”
However, the study did take some account of the effect of lifestyle on results. The study also uncovered detail about age and sex differences in the preferences against circadian rhythms. Dr. Kim comments:
“Considering many younger people are evening chronotypes, the metabolic risk associated with their circadian preference is an important health issue that needs to be addressed.”
The survey found that most participants did not identify themselves either as morning or evening types against the MEQ (Horne-Ostberg morningness-eveningness questionnaire) - 64.5% registered as neither. The remainder, however, fell into one of these two “extremes” in the sleep-wake cycle:
480 participants were classified as morning chronotypes (29.6%)
95 were categorized as evening chronotypes (5.8%).
In addition to the finding that all evening types overall were more likely to have diabetes and sarcopenia, a condition in which the body gradually loses muscle mass, results showed sex and age differences:
Men who were evening chronotypes were more likely have diabetes or sarcopenia than early risers
Women night owls tended to have more abdominal fat and a greater risk of metabolic syndrome compared with morning-ness
Evening chronotypes, while tending to be younger, had higher body fat and blood triglyceride levels than morning chronotypes.
Across all the men and women of all ages in the study, the increased odds in the evening type versus morning type of having diabetes was represented by an odds ratio of 1.73 (odds of diabetes in the one group were 1.73 times higher than the odds in the other group), while for metabolic syndrome the OR was 1.74 and for sarcopenia, 3.16 - all independent of total sleep duration and lifestyle.
The study controlled for potentially confounding factors by producing odds ratios that were adjusted to take account of age, gender, body mass index (BMI), smoking, alcohol, exercise, occupation, sleep duration and use of antihypertensive, antidiabetic or antilipid drugs.
Visceral obesity was a greater risk for night-owl women but was not, overall, significantly associated with chronotype. In women but not men, evening chronotype was associated with high waist circumference, triglyceride levels, and visceral fat - a finding that the authors say “might explain the increased risk of metabolic syndrome in women with evening type.” The increased risk for the male night owls, on the other hand, was of diabetes and sarcopenia rather than metabolic syndrome.
A sub-finding in the study was for blood pressure measurements. The researchers “observed a higher systolic blood pressure among morning types, a finding in agreement with a previous study.”
But the authors suggest that the blood pressure differences could be explained by the normal diurnal rhythm of systemic blood pressure, which dips at night and surges at the time of waking in the morning.
With blood pressures typically being measured in the study between 8am and noon, the morning types could have been showing earlier morning surges of systolic pressures than evening types, the authors explain.
Written by Markus MacGill