Metabolic problems 'more likely in evening types than morning people'

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:

- Diabetes - 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."