Our mood, the seasons, and the workings of our brain
The last weeks of winter are passing by and the days are rapidly becoming longer in the northern hemisphere, where many of her inhabitants may be looking forward to leaving their low mood, lack of motivation, or sleepy mornings behind with the cold temperatures. What do we know about the way the seasons can affect our mind and body?
Mental wellbeing throughout the year
Many of us may be familiar with the experience of what is often colloquially referred to as the ‘winter blues’ - a dip in mood and energy when the days grow shorter and the temperatures fall. While not everyone may experience extreme mood changes, some struggle with persistent low mood often referred to as seasonal affective disorder (SAD). This is not strictly included as a diagnosis in the DSM-V, which instead mentions Major Depressive Disorder (MDD) with a seasonal pattern. Still, the importance of seasonality for psychiatry is widely accepted and increasingly investigated. A few weeks ago, a large study on 13,000 adults with depression showed that longer daylight exposure was linked to better sleep and mental health. Research also suggests that the onset of psychiatric disorders, such as schizophrenia, may show seasonal trends. The interest in seasonal variations in psychiatric illness is not all that recent, with some suggesting that the first speculations about seasonality in psychiatry emerged as early as the 17th century - but what is known about the changes in our biological systems throughout the seasons?
The seasons getting under our skin
The earth’s seasons affect our immediate surroundings through physical changes such as temperature and exposure to natural daylight. Not only that, the seasons are said to affect our internal biology too. For instance, scientists have shown that seasonal cycles can affect gene expression. Whereas we may be born with a determined set of genes, the extent to which these genes are expressed can be influenced, for instance by our environment. Due to this, different types or amounts of protein may be transcribed from our DNA, which may lead to further changes in downstream biological processes, for instance via hormonal systems. The study found that the brain was one of the most notable tissues in which these seasonal changes could be seen.
Yet gene expression is not the only biological mechanism that is susceptible to seasonal variation. Last year, a fascinating discovery was made by researchers that the seasons affect the metabolism of glucose in the brain - in other words, the organ’s fuel usage. This fuel usage can be interpreted as a proxy for regional brain functioning. Different brain regions were found to reach a peak in their functioning at different times in the year, such as the winter or summer solstice, as well as the spring and autumn equinoxes (when daylight exposure changes the fastest).
Even our neurotransmitter systems in the brain, such as the dopamine and serotonin systems, are likely influenced by the seasons. Serotonin and dopamine systems play a crucial role in our day-to-day functioning and are targeted by many psychiatric medications like antidepressants. Not so surprisingly, researchers have suggested that clinicians may consider seasonal-dependent administration of psychiatric medication, and they are not the first to suggest seasonal-dependent drug therapy.
These are just a few examples of the growing interest and research efforts uncovering the science behind how our body’s biological systems may vary with the seasons. To what extent these variations contribute to and can explain the observed seasonal changes in mental health problems is yet to be studied in full detail. Could seasonal deviations in mental health be related to extreme biological changes in individuals (a biological ‘overreaction’) or rather a reduced ability of an individual’s biological systems to appropriately adapt to the seasons? And what may be the mechanisms by which these seasonal changes act on our biological systems, such as daylight exposure, temperature, or exposure to infectious agents? The growing interest raises more questions, and more research is necessary to better understand and appropriately treat seasonal mental health problems.