SEATTLE, WA—At SLEEP 2015, researchers from the Center for Circadian and Sleep Medicine, Northwestern University, Chicago, IL, proposed that a shorter phase angle is associated with a higher body mass index (BMI), body fat, and poorer dietary habits.

The observational study enrolled patients (n=97) with a sleep duration of ≥6.5 hours as determined by an actigraphy. Dim light melatonin onset (DLMO) was analyzed by blood samples and all patients took self-report questionnaires and completed 7 days of wrist actigraphy. Data was analyzed through correlations and regression analyses with controls for covariates such as age, gender, and sleep duration.

At baseline, average sleep duration was 443.7 minutes and average BMI (24.0kg/m2) and body fat (30.4%) percent were non-obese. The average DLMO was 22:48 (standard deviation 1:27) with an average sleep midpoint of 4:42. The phase angle between DLMO and sleep midpoint was 6:06 (standard deviation 1.07) hours.  The control variables were age, gender, sleep duration, DLMO, and sample day.

Study authors concluded that phase angle was inversely associated with body fat (r=-0.35; P=0.04) among male patients only where a shorter phase angle was linked to higher body fat. Among women, however, phase angle was not associated with BMI or body fat percentage. Overall, a shorter phase angle appeared to be linked to higher calorie, carbohydrate, and fat intake for both men and women (P<0.05). “As predicted, a later DLMO tended to result in a shorter phase angle,” reported Kelly Glazer Baron, PhD, the study’s lead author. “After controlling for age, the association with dietary intake remained significant.”

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Based on the study’s findings, Dr. Baron and colleagues were able to conclude that circadian misalignment in everyday life may impact risk for obesity.