Hyperactivity in anorexia nervosa: warming up not just burning-off calories

Abstract

Excessive physical activity is a common feature in Anorexia Nervosa (AN) that interferes with the recovery process. Animal models have demonstrated that ambient temperature modulates physical activity in semi-starved animals. The aim of the present study was to assess the effect of ambient temperature on physical activity in AN patients in the acute phase of the illness. Thirty-seven patients with AN wore an accelerometer to measure physical activity within the first week of contacting a specialized eating disorder center. Standardized measures of anxiety, depression and eating disorder psychopathology were assessed. Corresponding daily values for ambient temperature were obtained from local meteorological stations. Ambient temperature was negatively correlated with physical activity (p = -.405) and was the only variable that accounted for a significant portion of the variance in physical activity (p = .034). Consistent with recent research with an analogous animal model of the disorder, our findings suggest that ambient temperature is a critical factor contributing to the expression of excessive physical activity levels in AN. Keeping patients warm may prove to be a beneficial treatment option for this symptom.

Figure 1. Physical activity over daily hours for the Warm and Cold groups.

Mean (SEM) physical activity over daily hours (counts/hour) for the Warm and Cold groups (3-days measurement). Overall activity was higher for the Cold group, p<.01.

Figure 2. Differences in physical activity as a function of AT for a subsample of 8 patients.

Mean (SEM) physical activity levels (counts/day) as a function of AT for a subsample of 8 patients that showed a >4°C difference of AT over consecutive days. AT =  lowest mean AT; Δ AT =  mean difference between the lowest and highest AT. Patients were more active at lower AT, *p<.05. Cohen’s d = 0.89.