BENGALURU: Seasonal affective disorder (SAD) is a mysterious entity but there’s a lot of common sense to it when you look at it intuitively. Look at the phenomenon in nature, in both the plant and animal kingdom. In certain species like the polar bear, hibernation in winters is well known and an extensively studied phenomenon. Similarly, in the plant kingdom we all see the shedding of the leaves in fall leading to nearly barren trees all around us with the onset of the winters. Scientifically, we know that all living
beings are made up of water mainly and depend primarily on sunlight to survive and thrive. It makes logical sense to conclude that we as humans will have to endure the same physiological phenomenon, albeit in a more subtle way.
Researchers have tried to understand SAD for decades, although, there is some clarity on its existence and definition, its causation has been shrouded in mystery. There are three major hypotheses to understand the cause of it at a physiological level:
Shifting of the sleep-wake cycle
Sleep-wake cycle management is a very complex mechanism; we are beginning to understand the nuances of these in recent times. Essentially, the amount of light we are exposed to leads to the activation-deactivation of reticular activating system. Hence in winter months when the amount of sunlight we are exposed to is diminished we tend to experience a need for more sleep and feel tired more than during summer months. The mechanism of this phenomenon is fascinating to say the least. The advent of light therapy for treating SAD has been an interesting development. However, the amount, type and duration light therapy remains unclear, research on this is ongoing. There is also the issue of geographical location, SAD is a bigger problem in temperate countries compared tropical country like ours.
Neurotransmitter changes in the brain
It is a well known fact that serotonin dysfunction is very important when we are exploring the causation of depression. In recent studies the link between sleep-wake cycle disturbance and serotonin dysfunction has been established. In fact, one of the antidepressant medication Agomelatine (US FDA approved) is based on these findings.
Genetic vulnerability of individuals
When we look at the rate of SAD in any given population, the question that, why only some individuals suffer from SAD is understood, when we include genetic predisposition to depression into account. SAD is classed as depressive illness and is used only as specifier in diagnostic categories.Hence, we can conclude by saying that SAD is a multifactorial phenomenon. We have come a long way in understanding it but a lot remains to be explored.
The author is a psychiatrist and head at Mpower, The Centre