Mice Robbed of Darkness Fatten Up - Article Example

A Review of the Article “Mice Robbed of Darkness Fatten Up” Recent statistical figures reveal that the world’s obesity and metabolic disorder rates show a persistently increasing trend at the same time that people are more exposed to light at night or commonly referred to as LAN. It has been known that the body follows a particular biological clock referred to as “Circadian Rhythm.” The term circadian traces back its roots to the Latin words circa, which means around, and dies, which means day. It refers to biological processes in plants and animals that repeat in 24-hour cycles (American Heritage Dictionary of the English Language (3rd ed.)). A number of behavioral and autonomic processes in humans are generally affected by the body’s circadian rhythm. Among these processes include locomotor activity, feeding, excretion, sensory processing, and learning capability, control of body temperature, cardiovascular function, melatonin secretion, cortisol secretion, and sleep. It has also been a well established fact that light emitted by fluorescent lamps and other artificial sources fools the body into thinking that it is daylight and thus contributes to the disruption of the body’s circadian rhythm (Shneerson, 2005). Proponents of the study suggest that not only does LAN disrupt the body’s circadian functions, but it consequently causes metabolic processes as well. Establishing this proposal to be true is crucial because it could point to a crucial factor in the increasing obesity rates of the world’s population, that is, the increasing use of artificial lights in our environment. Thus, the article is asking the following: Does exposure to light at night change the body’s circadian rhythm and affect metabolic processes? In other words, is there a causal relationship between a subject’s exposure to light at night and his / her circadian rhythm? Does this causal relationship consequently affect metabolic processes, and ultimately, weight? More specifically, is this causal relationship direct, that is, does exposure to light at night cause obesity? Furthermore, this question implies another one: Is our increasingly artificially lighted environment causing us to be more obese? In order to answer these pertinent questions, the authors of the study hypothesized that if there is indeed a direct causal relationship between exposure to night light, circadian rhythm and weight, then subjects exposed to LAN should have a significantly increased body mass. In addition, subjects exposed to LAN should also have reduced glucose tolerance and altered stress levels. Finally, LAN is hypothesized to induce locomotor arrhythmicity. All these effects are supposed to indicate that LAN exposure significantly alters a body’s circadian rhythm. There were two experiments in the discussed study. Both experiments saw three groups of mice subjected to different lighting conditions. The LD group was subjected to the standard light/dark cycle, the DM group was subjected to dim light conditions, and the LL group was exposed to continuous lighting. The experimenters ought to be commended on considering a third group, the DM group as a middle ground between the two “extreme” lighting conditions. Since mice in in constant lighting have no temporal cue to distinguish time of day, and their biological clocks free-run, the DM group may more directly model environmental light pollution experienced in industrialized nations. In addition, including the LL group allowed the researchers to focus not only on the effects of light pollution but also on the effects of a “desynchronized circadian system on metabolism.” The first experiment did not pose extra restrictions on the mice, that is, they were given unrestricted access to a food source during both light and dark phases. The second experiment considered that the effects of altered timing of food consumption may intervene with the changes in the body mass of the DM group. Thus, in this second experiment, mice housed in either LD or DM conditions had continuous access to food (FA) or had food access limited to either the light (FL) or dark (FD) phase. Unfortunately, while the tests were properly controlled, they did not go through replications. Replications of the tests would lend more integrity to the results especially if results in the replications are statistically similar as in the results of the original test. The study was conducted under the following assumptions: 1) The experimental mice retain some responsiveness to photoperiod. 2) Typical light / dark phases should be timed such that he light phase runs for 16 hours while the dark phase runs for 8 hours. Proponents of the study predicted that the effects of light at night exposure to circadian rhythm will manifest itself more dominantly on the group subjected to continuous lighting. Proponents expected that those in the DM and LL groups would experience a significant increase in body mass and a reduced glucose tolerance level. Furthermore, the stress levels of the subjects belonging to these groups would be altered and that their locomotor skills would be considerably arrythmic. Findings reveal that mice housed in either bright (LL) or dim (DM) LAN have significantly increased body mass and reduced glucose tolerance compared with mice in a standard (LD) light/dark cycle. This is despite the fact that the mice in all three groups had equivalent levels of caloric intake and total daily activity output. Furthermore, the timing of food consumption by DM and LL mice differs from that in LD mice. Rodents who come out at night typically eat substantially more food at night; however, DM mice consume more of their food during the light phase, as compared with LD mice. Moreover, findings indicate that restricting food consumption to the active phase in DM mice prevents body mass gain. These results generally coincide with two of the hypotheses that were established by the proponents. Incidentally, the experiments did not provide sufficient evidence to conclude that disrupted circadian rhythms altered stress levels or locomotor skills. In conclusion, this study provides a significant amount of evidence which supports the idea that inappropriate exposure to artificial light does disrupt circadian rhythm, at least, for the mice involved in the study. Furthermore, other than altering metabolic processes that lead to weight gain, nighttime lighting likewise significantly reduces glucose tolerance. Thus, the study provides significant contribution to literature that supports the claim that current trends in rising obesity rates may be partially attributed to increased and inappropriate exposure to artificial lights. Moreover, this study, if applicable to humans, signifies that the time of food consumption may just be as important a consideration as the amount of food consumption. References American Heritage Dictionary of the English Language (3rd ed.). (1992). MA: Houghton Mifflin Company. Fonkena, L., Workman, J., Walton, J., Weila, Z., Morris, J., Haim, A., et al. (2010). Light at night increases body mass by shifting the time of food intake. Raloff, J. (2010, November 6). Mice robbed of darkness fatten up: Time of day can affect calories impact. Shneerson, J. (2005). Sleep medicine: a guide to sleep and its disorders. John Wiley & Sons. Read More