Prolonged daily light exposure increases body fat mass through attenuation of brown adipose tissue activity
Increased light exposure has been associated with obesity in both humans and mice. In this article, we elucidate a mechanistic basis of this association by performing studies in mice. We report that prolonging daily light exposure increases adiposity by decreasing energy expenditure rather than increasing food intake or locomotor activity. This was caused by a light-exposure period-dependent attenuation of the noradrenergic activation of brown adipose tissue that has recently been shown to contribute substantially to energy expenditure by converting fatty acids and glucose into heat. Therefore, we conclude that impaired brown adipose tissue activity may mediate the relationship between increased light exposure and adiposity.
Disruption of circadian rhythmicity is associated with obesity and related disorders, including type 2 diabetes and cardiovascular disease. Specifically, prolonged artificial light exposure associates with obesity in humans, although the underlying mechanism is unclear. Here, we report that increasing the daily hours of light exposure increases body adiposity through attenuation of brown adipose tissue (BAT) activity, a major contributor of energy expenditure. Mice exposed to a prolonged day length of 16- and 24-h light, compared with regular 12-h light, showed increased adiposity without affecting food intake or locomotor activity. Mechanistically, we demonstrated that prolonged day length decreases sympathetic input into BAT and reduces β3-adrenergic intracellular signaling. Concomitantly, prolonging day length decreased the uptake of fatty acids from triglyceride-rich lipoproteins, as well as of glucose from plasma selectively by BAT. We conclude that impaired BAT activity is an important mediator in the association between disturbed circadian rhythm and adiposity, and anticipate that activation of BAT may overcome the adverse metabolic consequences of disturbed circadian rhythmicity.
Why is conclusion doubtful? Simple. Most of the study is based of measurements of British females. Not a country known for it’s prolonged natural daylight. As in the high Andes people adapted to shortage of oxygen by having a vastly improved oxygenation system, so do people with a shortage of daylight adapt as well.
Extrapolating this effect (if it’s there indeed) measured in the higher northern hemisphere to humanity in general is patently absurd. Again the new age way of thinking such a thing as ‘obesity’ can be objectively measured infiltrates formerly scientific reason.
For example being of a certain weight is a cultural thing. In many cultures being skinny means you’re poor, being not so is sign of affluence. In many African cultures being ample bodied is a sign of fertility in females. It’s hard to imagine this just came about without reason, more reserves to bear children comes to mind.
Only in the limited view of a part of western affluent world is being skinny a sign health. Which it isn’t. Skinny people are more often ill, are so longer, recover more slowly from hospital interventions and have little resistance to all nasty things nature can throw at a human.