Is Light Making Us Fat?

Is Light Making Us Fat?

By Marc Tawfik, Biochemistry, 2018

Prolonged light exposure might be making us fat. Numerous past studies have established a link between light exposure and circadian rhythm- the body’s “internal clock” that regulates one’s sense of wakefulness. Excessive exposure to light can disrupt the normal electrical activity in a specialized region of a part of the brain known as the hypothalamus. This specialized region, the suprachiasmatic nucleus (SCN), is responsible for controlling circadian rhythm. Prolonged exposure to light and the resulting disruption of the internal body clock has been linked to increased rates of obesity.

A study published recently in the Proceedings of the National Academy of Sciences by a group of scientists from the Netherlands explored the biological mechanism potentially responsible for this link and its implications for modern society.

In a previous study, the scientists found that prolonged light exposure resulted in weight gain in mice without any visible increase in food consumption or decrease in physical activity. The group therefore hypothesized that perhaps the bodies of the mice were somehow expending less stored energy, leading to more energy being kept as fat. To explore this hypothesis, the scientists designed a study to investigate the effect of light exposure on the activity of brown adipose tissue in relation to weight gain in mice.

Brown adipose tissue (BAT) is a type of fat tissue found in mammals that functions primarily to convert energy into body heat by combusting triglycerides, fat molecules produced from unused calories. BAT was a particularly good candidate for investigation as its function is partially influenced by the SCN of the hypothalamus.

The study divided mice into three groups based on the length of time daily they would be exposed to light; 12, 16, or 24 hours. After five weeks, the mice were weighed and sacrificed for deeper analysis. Interestingly, the researchers found that prolonged light exposure did not significantly change the overall body weight or lean mass of the mice. However, the scientists observed that daily light exposure correlated with a significant increase in fat mass when comparing mice who were exposed daily to light for 24 hours to those exposed for 12.

When compared to mice who were exposed to 12 hours of light, mice who had been exposed for 24 hours had 57% more fat mass and 21% larger body fat deposits. Slight increases in fat mass and deposit size were observed in the mice exposed to light for 16 hours.

To monitor BAT activity in the mice, the scientists injected the mice with radiolabeled fatty acids derived from triglycerides that served as tracers. The group found that length of light exposure was negatively associated with BAT’s ability to uptake fatty acids, with the 24 hour exposure group showing up to a 48% decrease in fatty acid uptake compared to the 12 hour group. Further analysis revealed that prolonged light exposure is associated with disrupted expression of the genes and chemical signaling pathways mediated by the SCN that are responsible for maintaining proper BAT function, providing a potential explanation for diminished BAT activity.

The group’s study strongly suggests that prolonged light exposure indirectly diminishes BAT activity in mice and thus leads to increased body fat. Prolonged light exposure disrupts the normal function of the SCN region of the brain, which leads to the diminished BAT activity and thus a decreased ability for the body to burn fat. As this is likely true in humans as well as mice, it may be wise to minimize excess artificial light exposure. Start by taking steps to properly darken your bedroom before sleeping and cutting back on the time spent in front of a computer screen.