Dim light at night increases body mass of female mice

Abstract

During the past century, the prevalence of light at night has increased in parallel with obesity rates. Dim light at night (dLAN) increases body mass in male mice. However, the effects of light at night on female body mass remain unspecified. Thus, female mice were exposed to a standard light/dark (LD; 16 h light at ∼150 lux/8 h dark at ∼0 lux) cycle or to light/dim light at night (dLAN; 16 h light at ∼150 lux/8 h dim light at ∼5 lux) cycles for six weeks. Females exposed to dLAN increased the rate of change in body mass compared to LD mice despite reduced total food intake during weeks five and six, suggesting that dLAN disrupted circadian rhythms resulting in deranged metabolism.

Keywords: Body mass regulation; circadian disruption; light at night; light pollution.

Figure 1. Female mice exposed to dim light at night (dLAN) had a greater change in body mass than mice exposed to dark nights (LD), despite decreased food intake in dLAN mice compared to LD mice in weeks five and six

Body mass interacted with lighting across the six weeks of the experiment such that mice in dLAN (n=11) had a greater gain in body mass than mice in LD (n=9) (A). Change in body mass was increased in dLAN (n=11) mice compared to LD (n=9) mice across the six weeks of the experiment (B). Food intake across the six weeks of the experiment, LD (n=8) mice had increased food intake on weeks five and six compared to dLAN (n=11) exposed mice (C). Mice in LD (n=7) and dLAN (n=8) had similar amounts of 24 hour (h) activity averaged for the four days of home cage monitoring (D). Significant mean differences p<0.05 indicated by asterisk (*).