Nutrition in the spotlight: metabolic effects of environmental light

Abstract

Use of artificial light resulted in relative independence from the natural light-dark (LD) cycle, allowing human subjects to shift the timing of food intake and work to convenient times. However, the increase in artificial light exposure parallels the increase in obesity prevalence. Light is the dominant Zeitgeber for the central circadian clock, which resides within the hypothalamic suprachiasmatic nucleus, and coordinates daily rhythm in feeding behaviour and metabolism. Eating during inappropriate light conditions may result in metabolic disease via changes in the biological clock. In this review, we describe the physiological role of light in the circadian timing system and explore the interaction between the circadian timing system and metabolism. Furthermore, we discuss the acute and chronic effects of artificial light exposure on food intake and energy metabolism in animals and human subjects. We propose that living in synchrony with the natural daily LD cycle promotes metabolic health and increased exposure to artificial light at inappropriate times of day has adverse effects on metabolism, feeding behaviour and body weight regulation. Reducing the negative side effects of the extensive use of artificial light in human subjects might be useful in the prevention of metabolic disease.Artificial light: Circadian: Glucose metabolism: Obesity Changes in artificial light exposureObesity is an increasing health problem and is associated with the development of type 2 diabetes and CVD (1) . The pathophysiology of obesity is multifactorial, with the major contributions from overconsumption of highenergy highly palatable food and an inactive lifestyle (2) . One modern environmental factor that contributes to changes in eating behaviour is the widespread use of artificial light. The relative independence from the natural light-dark (LD) cycle, allows people to eat and engage in activities until late in the evening and at night. Artificial light has also led to an increase in nighttime sky glow and to the transformation of nightscapes. More than 99% of the US and EU population, and about two-thirds of the world population lives in areas where the night sky is illuminated above the threshold for light pollution (artificial sky brightness greater than 10% of the natural night sky brightness above 45°eleva-tion). Moreover, satellite data show that 70% of the US population and 50% of the European population can no longer see the Milky Way, even under the best conditions (3) . Cinzano et al. (3) calculated that only 40% of Americans live in a location where it becomes sufficiently dark at night for the human eye to make a complete transition from cone to rod vision. Despite the benefits for

Blue light at night acutely impairs glucose tolerance and increases sugar intake in the diurnal rodent Arvicanthis ansorgei in a sex‐dependent manner

“…Animal and human studies providing evidence of the metabolic effects of environmental light have been reviewed extensively (Cho et al ; Versteeg et al ). In humans, increases in obesity and diabetes match increased artificial light exposure (Fonken and Nelson ) and it has been demonstrated that evening bright light increases appetite (AlBreiki et al ).…”

Blaming the Brain for Obesity: Integration of Hedonic and Homeostatic Mechanisms

“…Among the many potential environmental factors causing obesity, reaching from viruses 72 through toxins 73 to the use of artificial light 74 , changes in nutrition and food hedonics have attracted the most attention. Particularly the shift away from relatively low-calorie, high-fiber diets towards energy-dense, palatable diets is considered an important contributor to the increased prevalence of obesity.…”

The Circadian Syndrome: is the Metabolic Syndrome and much more!

“…An important background perspective to this scenario is the escalating global epidemics of type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD) against the dramatic changes that have occurred in Western and even traditional‐living societies over recent decades with globalization and modernization . This includes changes in light exposure resulting from the extensive use of artificial light (‘light pollution’) , controlled ambient temperature and constant food availability , societal and workplace stresses, increasing shift work in the workplace and industry, jet travel with time zone changes and changes in nutrition. In the light of this, it has been suggested that the resulting circadian rhythm disturbances may be a major contributor to the contemporary global epidemics of T2DM, CVD and obesity .…”

“…It regulates gene expression, release of various hormones, body temperature, activity pattern, energy expenditure and other important body functions. This being the case, it is not surprising that there has been significant interest in the relationship of circadian disruption with glucose metabolism [5,13,15,16,18,21,22] and other components of the Metabolic Syndrome [6,17,19,22,23].…”