In the study involving 51 people, night owls metabolized fat less efficiently, showed less insulin sensitivity, and demonstrated lower physical fitness than early birds, lead author Steven K. Malin, PhD, of Rutgers University, New Brunswick, N.J., and colleagues reported.
Prior publications have suggested that night owls, formally known as “late chronotypes,” have an increased risk of obesity, type 2 diabetes, and cardiovascular disease, Dr. Malin said in an interview. But no previous research involved the gold-standard measurement tools used in this study, including euglycemic clamp and indirect calorimetry to quantify fat metabolism.
Dr. Malin also noted that this is the first study of its kind to characterize metabolism during both rest and exercise.
The study, published in Experimental Physiology, involved 24 early birds and 27 night owls classified by the Morning-Eveningness Questionnaire. All participants were sedentary, reporting less than one hour of structured exercise per week, and had metabolic syndrome according to Adult Treatment Panel III report criteria. Groups were otherwise demographically similar, with average ages in each group of approximately 54-55 years.
Compared with night owls, early birds were more physically active during the morning into midday. During exercise, they metabolized more fat and demonstrated greater physical fitness based on VO2max readings. At rest, early birds also came out ahead – they had higher fat oxidation and non–oxidative glucose disposal, suggesting more sensitivity to insulin.
“Collectively, this work highlights and supports chronotype as a potential risk factor related to type 2 diabetes and cardiovascular disease risk,” the investigators concluded.
Night owls have less metabolic control
Jed Friedman, PhD, director of OU Health Harold Hamm Diabetes Center at the University of Oklahoma Health Sciences Center, Oklahoma City, praised the study for the size of the groups the researchers compared with each other and how well matched those groups were, as well as the “state-of-the-art” measurement tools employed.
The findings show that night owls have “less metabolic control,” Dr. Friedman said in an interview.
“That’s a term that’s frequently invoked in [regard to] prediabetes,” he said. “Blood sugar goes up, because when you’re eating a high carbohydrate diet, your cells aren’t metabolizing sugar properly. That tends to raise your risk for a lot of diseases.”
Dr. Friedman added that the findings align with those of previous studies that have linked less sleep with changes in brain biology, and therefore behavior, especially in dietary choices.
“When you’re tired, the mechanisms for appetite control go haywire,” Dr. Friedman explained. “The evidence suggests that sugar is the primary driver for what people eat when they’re tired. That obviously has implications for diabetes and metabolic syndrome. So sleeping more really can help you control cravings.”
Dr. Friedman also noted that people who are tired tend to engage in less physical activity, further increasing their risk of metabolic issues. To control this risk, he advised people to return to their circadian rhythms, which could mean forgetting the midnight snack.
“Having a daily pattern that’s in sync with chronicity, or these daily rhythms, is associated with greater health,” Dr. Friedman said. “We’re not really made to eat at night. I think this [study] kind of reinforces that.”