Greased lighting : implications of circadian lipid metabolism for cardiometabolic health

Cardiovascular diseases (CVD) are the leading cause of death worldwide, and disturbances in day-night rhythms have recently been implicated as a novel risk factor for CVD. We investigated the effects of modulating circadian rhythms on energy metabolism using animal models and by studying plasma metaoblites and lipids in humans. Using animal studies we observed that brown adipose tissue (BAT) is strongly regulated by the biological clock, possibly via circadian glucocorticoid rhythms, and attenuated BAT activity through prolonged light exposure increases adiposity. Research focusing on the rhythm in human BAT, and regulation thereof, is necessary to confirm the translational value of our findings. We also observed that mistimed light exposure enhances atherosclerosis development, which may provide a mechanistic link between the known association between shift work and CVD. We anticipate that living according to the natural circadian rhythms presumably contributes to cardiometabolic health. Since disturbances in day-night rhythms are inevitable in modern society, in the future we may advise individuals at risk for development of CVD refrain from shift work and short sleep duration. In addition, data in this thesis may be useful to design strategies to avoid the disadvantageous metabolic effects of shift work.