Letters to the Editor
Bright Light, Serotonin Turnover, and Psychological Well-Being
Relatively little is known about healthy people in terms of seasonal and weather influences and the effects of exposure to bright light on their serotonergic system and psychological well-being. Recently, Lambert and others reported that the rate of production of serotonin by the brain was directly related to the prevailing duration of bright sunlight and rose rapidly with increased luminosity (1). Studies indicate that exposure to bright light improves the psychological condition (2). The scientific literature also suggests that increased humidity tends to be related to decreased concentration and increased sleepiness, and uncomfortable temperature is associated with increased aggressive behaviour (3). Most likely, a psychobiological response to seasonal and weather conditions is a result of interacting environmental and genetic factors. Genetic factors can interact with environmental factors in different ways, and 2 such mechanisms have been explored: “genetic control of sensitivity to the environment” and “genetic control of exposure to the environment” (4). “Genetic control of sensitivity to the environment” suggests that genes in part render individuals relatively vulnerable or relatively invulnerable to the effects of seasonal and weather conditions. For example, the effect of light deprivation may be substantially greater in those at high vs low genetic risk for seasonal changes in mood and behaviour (seasonality). “Genetic control of exposure to the environment” suggests that genetic factors influence the probability that individuals will select themselves into certain environments. For example, the genetic risk factors for seasonality may in part express themselves by influencing the probability that individuals will spend more time indoors.
Both genetic and environmental factors operate, at least in part, through the brain serotonergic system (1,5–7). Molecular genetic studies of seasonality have focused on serotonin, and especially on the role of the serotonin transporter gene, in the neurobiology of seasonality (5–7). It has been reported that a serotonin transporter gene polymorphism is associated with seasonality in the general population (5,6). Possibly, the serotonin transporter gene affects both sensitivity and exposure to the environment.
Exposure to bright light is important for psychological well-being. In the modern industrial world, many people spend a lot of time indoors. They are light-deprived and have a sedentary lifestyle. Combined exposure to bright light and physical exercise can be especially effective for improving mood- and health-related quality of life (2). Various outdoor activities may provide good opportunities to improve health.
1. Lambert GW, Reid C, Kaye DM, Jennings GL, Esler MD. Effect of sunlight and season on serotonin turnover in the brain. Lancet 2002;360:1840–2.
2. Partonen T, Leppämäki S, Hurme J, Lönnqvist J. Randomized trial of physical exercise alone or combined with bright light on mood and health-related quality of life. Psychol Med 1998;28:1359–64.
3. Young MA. Weather. In: Partonen T, Magnusson A, editors. Seasonal affective disorder. Practice and research. Oxford: Oxford University Press; 2001. p 169–73.
4. Kendler KS. Major depression and the environment: a psychiatric genetic perspective. Pharmacopsychiatry 1998;31:5–9.
5. Sher L, Greenberg BD, Murphy DL, Rosenthal NE, Sirota LA, Hamer DH. Pleiotropy of the serotonin transporter gene for seasonality and neuroticism. Psychiatr Genet 2000;10:125–30.
6. Sher L. Genetic studies of seasonal affective disorder and seasonality. Compr Psychiatry 2001;42:105–10.
7. Rosenthal NE. Winter blues: seasonal affective disorder: what it is and how to overcome it. Rev. ed. New York: The Guilford Press; 1998.
Leo Sher, MD
New York, New York