According to John Keats, in his poem The Human Seasons, ‘Four seasons fill the measure of the year; There are four seasons in the mind of men.’ One of many literary figures to compare the phases of life to the seasons, Keats was also a medical man and a Licentiate of the Society of Apothecaries.
As a man thought to have been periodically afflicted with depression, probably brought on by the largely-unrequited nature of his love affair with Fanny Brawne, Keats might have been in the ideal position to hypothesise on how the seasons and one’s thinking are intricately linked. Alas, he also suffered from tuberculosis and sadly died while barely in the summer of his own life.But is there any truth to this idea that the seasons affect our mood? Certainly, the diagnosis of seasonal affective disorder (SAD) has long been established, with the classical presentation traditionally thought to be that of depression with reversed biological features in winter. Some commentators have suggested there is evidence of a bipolar-type illness in some patients, with mild hypomania occurring in spring or summer. In addition, mixed patterns are also thought to exist for some individuals.
h4. Seasonal component
So, what evidence is there to back up the existence of this seasonal component? A Norwegian study by Morken and colleagues examined the rate of admissions to psychiatric hospitals, with particular reference to patients with affective illnesses (1). Over 35,000 such admissions were examined, with significant monthly variations noted in admissions for depression. There were gender differences, moreover, with such admissions peaking in November for women and in April for men.
Shapira and colleagues took this idea one step further by examining whether it matters if such depressive episodes are in the context of unipolar or bipolar affective disorder (2). Their Israeli study looked at the influence of various climactic factors on admission rates amongst 5,000-or-so depressed patients, further taking into account which type of affective disorder each participant had.
They found significant seasonal variation amongst the bipolar depressed patients (who represented approximately 80 per cent of the sample) with higher mean monthly admission rates in spring and early summer, and a significant correlation between admission rates and mean maximal monthly environmental temperature. Such results, surprisingly, were not seen amongst the unipolar depressed patients.
So, if bipolar patients with depression show seasonal variations in admission rates, can the same be said for those with mixed-affective or manic states? Probably so, according to Cassidy and colleagues, who examined 300-or-so such admissions over a three-year period (3). It was found, however, that, although the frequency of manic episodes peaked in early spring, the mixed-manic admission rates peaked in late summer. This picture becomes a little more complicated when we take Heon-Teong and colleagues’ study of seasonality and first-episode mania into account (4). The authors examined 152 such patients in two hospitals over a three-year period and observed a cluster of 25 new cases that presented during March. They also noted, however, that sunlight radiation intensity and hours of daily sunshine correlated significantly with manic episodes overall – but only for manic patients who had experienced a major depressive episode in the past. To further complicate matters, the authors separated the participants by gender and found that the correlation with sunlight radiation existed for females and not for males.
So, if seasonality is influenced by gender, what about ethnicity? This was addressed to some degree by Guzman and colleagues in Washington DC last year (5). In their study, they examined the amount of seasonality – and the prevalence of both winter-type and summer-type SAD – in two groups of college students, one of African-immigrant extraction and one of African-American extraction.
In total, 246 of the former and 599 of the latter completed the Seasonal Pattern Assessment Questionnaire (SPAQ). In a complex interaction between ethnicity and awareness of SAD, a greater percentage of African students reported seasonal mood changes (especially summer-type SAD) in comparison to African-American students. It was suggested this may be due to incomplete acclimatisation to a higher latitude and a temperate climate.
Meanwhile, Soriano and colleagues examined seasonality of mood in a group of predominantly Caucasian participants who lived in regions with hot summers but a relative lack of air conditioning (6). Given prior evidence that seasonal depression may be linked to a vulnerability to heat exposure, the authors were interested in whether participants with access to air conditioners might experience lower rates of SAD than those without access.
h4. Summer-type SAD
The SPAQ was completed by 476 Romanian postgraduate students, in whom the authors found lower rates of summer-type than winter-type SAD, a result in keeping with other studies. Access to air conditioners, however, was associated with higher rates of summer-type SAD. But why is there a seasonal variation at all? Various theories exist, most interestingly that of Lambert and colleagues, who suggest that it may be related to seasonal changes in monoaminergic neurotransmission (7). In their examination of serotonin metabolite concentrations in the blood samples from 101 healthy men, they found the neurotransmitter’s turnover was lowest in winter.
They also noted that the rate of serotonin production by the brain correlated closely with participants’ duration of exposure to bright sunlight, with production rising rapidly when sunlight was increased. Their findings added significantly to the evidence that serotonin release influences the seasonal nature of mood in general.
Not all studies have supported the influence of seasonality. Graf and colleagues, for example, interviewed 7,000-or-so adults aged between 16 and 64 years in order to detect seasonal variations in a range of illnesses from affective disorders to anxiety disorders, substance-misuse, eating disorders and schizophrenia (8). No statistically-significant seasonal difference was found, although there was a trend towards higher illness-prevalence in winter, particularly for the anxiety disorders.
A little closer to home, some studies have been conducted in the context of what might be termed our ‘uniquely-variable’ Irish climate. A few years ago, Clarke, Moran and colleagues spent some time examining seasonality with regard to affective disorders and schizophrenia (9).
h4. Admission statistics
Using the admission statistics from the National Psychiatric Inpatient Reporting System (NPIRS) on a year-to-year basis over a six-year period, they noted significant seasonal variations in monthly admission patterns for both types of illness, particularly the affective disorders. Interestingly, this seasonal pattern was not constant from year to year, especially in cases of schizophrenia.
A further study by the same authors compared a group of first-admissions and readmissions with affective disorders and schizophrenia over the same six-year period (10). While seasonality was noted to have a clear influence over first admissions with mania and readmissions with bipolar affective disorder, it was only found to influence schizophrenia for first admissions and not relapses.
Overall, it seems, the evidence is both plentiful and varied. Certainly the seasons seem to have an influence over admissions for bipolar affective disorder, be it for depressive, manic or mixed-affective states. Both gender and ethnicity appear to play a role in this phenomenon which, according to one Irish study, is inconstant from year to year, while aetiology theories range from serotonin turnover to heat exposure to even the presence or absence of air conditioning.
No doubt it is a complex process that we may understand in time. To finish, Keats might best have summed up the patient who succumbs to the seasons, had he applied his observation that, ‘He has his winter too of pale misfeature; Or else he would forego his mortal nature.’
1. Morken G, Lilleeng S, Olav LM. Seasonal variation in suicides and in admissions to hospital for mania and depression. Journal of Affective Disorders (2002). 69:39-45.
2. Shapira A, Shiloh R, Potchter O, Hermesh H, Popper M, Weizman A. Admission rates of bipolar depressed patients increase during spring/summer and correlate with maximal environmental temperature. Bipolar Disorders (2004). 6:90-93.
3. Cassidy F, Carroll BJ. Seasonal variation of mixed and pure episodes of bipolar disorder. Journal of Affective Disorders (2002). 68:25-31.
4. Heon-Jeong L, Leen K, Sook-Haeng J, Kwang-Yoon S. Effects of season and climate on the first manic episode of bipolar affective disorder in Korea. Psychiatry Research (2002). 113:151-159.
5. Guzman A, Rohan KJ, Yousufi SM, Nguyen MC, Jackson MA, Soriano JJ, Postolache TT. Mood sensitivity to seasonal changes in African college students living in the greater Washington D.C. metropolitan area. Scientific World Journal (2007). 7:584-91.
6. Soriano JJ, Ciupagea C, Rohan KJ, Neculai DB, Yousufi SM, Guzman A, Postolache, TT. Seasonal variations in mood and behavior in Romanian postgraduate students. Scientific World Journal (2007). 7:870-9.
7. Lambert GW, Reid C, Kaye DM, Jennings GL, Esler MD. Effect of sunlight and season on serotonin turnover in the brain. Lancet (2002). 360:1840-42.
8. De Graf R, van Dorsselaer S, ten Have M, Schoemaker C, Vollebergh WAM. Seasonal variations in mental disorders in the general population of a country with a maritime climate: findings from the Netherlands mental health survey and incidence study. American Journal of Epidemiology (2005). 162:654-661.
9. Clarke M, Moran P, Keogh F, Morris M, Kinsella A, Walsh D, Larkin C, O’Callaghan E. Seasonal influences on admissions in schizophrenia and affective disorder in Ireland. Schizophrenia Research (1998). 34:143-149.
10. Clarke M, Moran P, Keogh F, Morris M, Kinsella A, Larkin C, Walsh D, O’Callaghan E. Seasonal influences on admissions for affective disorders and schizophrenia in Ireland: a comparison of first and readmissions. European Psychiatry (1999). 14:251-5.