A biological overview of the seasonal changes across mood disorders
“The changes of the seasons are especially liable to beget diseases” — Hippocrates (5th century BC).
Here we are, April has come and is already about to end. We are now in the middle of the spring and approaching summertime, to the delight of many.
However, even if most of us are happy for the arrival of spring, this may be a very trying time for both our body and mind.
Spring is a period of great changes, not only in the landscape surrounding us.
The progressive and massive environmental development of the contemporary world have certainly detached us from changes in the natural world. We do not live in the wild, and we can vastly adjust the environment to our wishes.
Still, we are significantly affected by seasonal changes.
We just need to look outside. The days are getting warmer and the sun is staying out longer, increasing the daylight time. This has been further amplified early this month by the “summer time”, that forced us to reset our clocks to one hour ahead.
All these modifications could seem trivial, but they affect our wellbeing. Of course, under physiological conditions, our body is able to face them and react in a positive way. However, people suffering from mental illnesses may be hyper-sensitive to these changes.
These changes could actually be a trigger for the development or exacerbation of the disease.
The way our body reacts to this combination of external stimuli is multifaceted, and involves several biological factors in an intricate interaction orchestrated by our brain.
The light-dark cycle has a deep impact on the biology of the brain. In particular, there is a specific cerebral area, located in the very middle of the brain, which has been proved to be crucial in mediating these changes: the hypothalamus. It is strictly connected to the other brain areas and regulates several essential biological functions, for example hormone secretion and response to stress.
The hypothalamus contains a specific group of cells that regulate the so-called circadian rhythm, from the Latin circa: approximately, and diem: day.
We can think of it as an internal clock regulating a wide variety of biological functions within a 24-hour time frame. And health problems can be linked to a disruption of this rhythm.
Many of us have experienced the well-known “jet-lag”, often related to long-distance trans-meridian (east–west or west–east) travels, and mostly characterized by sleep disturbances and fatigue.
However, this 24-hour daily rhythm is also strictly related to a longer rhythm which covers the four seasons all over the year, known as circannual rhythm.
So, during seasonal changes our body must face a plethora of signals. This can destabilise our homeostasis, that is, our steady internal functioning, affecting also our mood.
Someone could feel happier and more energic, while others tired, fatigued, and listless.
Well, this may not be just the weather.
Indeed, specific psychiatric disturbances, such as mood disorders (depression, bipolar), are frequently sensitive to seasonal changes.
The arrival of spring, as well as autumn, could be associated with a failure in the biological adaptation of the body to the seasonal changes, leading to disrupted communication between the circadian (day) and circannual (seasonal) rhythms, and resulting in the onset of an episode of a mood disorder.
Seasonality and mood disorders
Mood disorders are disturbances of the basic individual’s affective status.
These may occur as a lower — depression — or an elevated — mania — mood compared to the subject’s normality. Both these conditions are pathological and related to severe and life-threatening consequences. Depressive disorders are characterized by the presence of depressive episodes only, while bipolar disorders by the presence of manic (or hypomanic, when less severe) episodes, besides depressive ones.
Seasonality is important in both depressive and bipolar disorders. A cyclical course, with recurrent episodes, is typical of mood disorders. Exacerbations and remissions may repeatedly occur at specific times of the year.
According to the diagnostic criteria of the last version of the most commonly used classification of mental disorders, the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), the presence of a “seasonal pattern” can be applied to both.
This means that patients with mood disorders could experience relapses and remissions of their illnesses recurrently at specific times of the year, usually in association with specific seasons.
Seasons and mental health have mostly been studied in relationship with the old concept of “seasonal affective disorder”. This is a peculiar subtype of depressive disorder, with recurrent depressive episodes in autumn-winter and remissions in spring-summer.
It is still the most common type of depression with seasonal features, also called “winter-depression”, and it is observed particularly in higher-latitude countries (for example, Scandinavia or Alaska) where variations in daylight across seasons are most marked.
It is also clear that mood alterations could involve not only depressive episodes, but importantly also manic (and hypomanic) ones.
Moreover, episodes of a mood disorder could be worsened not only in autumn-winter, but also during the spring-summer shift.
Mood disorders with seasonal features are quite common. Around 10% of depressed patients have a seasonal course. Even higher rates have been reported for bipolar disorders.
Seasonal depression is more frequent in younger persons and is often associated with a specific symptomatologic pattern, characteristic of the “atypical” subtype of depression, which includes increased appetite and need for sleep, and loss of energy.
These symptoms are also frequent in the bipolar form of depression (or bipolar depression), that is, depressive episodes occurring in people suffering from bipolar disorders.
Of note, patients with manic episodes have higher rates of admission into hospitals during spring and summer, when sunlight exposure is longer.
A seasonality effect is also present for the most tragic consequence of mood disorders, suicide, with rates that also increasein spring or early summer.
Clinical implications
From a psychiatric point of view, these observations are particularly important.
It is important that a correct diagnosis considers the life-time history of the patient, and specifically investigates seasonal patterns of relapse.
It is important also for patients and their relatives not to underestimate fluctuations in mood related to seasonal changes, promptly asking for help if needed.
Seasonality can also offer an opportunity to prevent (or at least be prepared for) an episode of a mood disorder.
Of note, a treatment specifically acting on circadian rhythms and counteracting the effects of light variations exists: light-therapy.
This treatment is effective in addition to antidepressant drugs for depressive episodes, mostly for those with a seasonal pattern.
“April showers bring May flowers”
Spring is certainly a particularly delicate time of the year for people with mental health problems, and changes in mood, appetite, energy or sleep during this period should be considered a wake-up call for clinicians and patients.
But it is not all just bad.
The knowledge of the potential effects of seasonal changes in some people with mental disorders can allow us toprevent or better treat recurrences, thus limiting their impact.
“Is my mental health problem seasonal?”
This is a question that all people suffering from a mood disorder should consider, and should try to answer together with their clinicians, in order to improve their mental health.
