Seasonal Effects on Hospitalizations Due to Mood and Psychotic Disorders: A Nationwide 31-Year Register Study

Abstract

Purpose To examine seasonal patterns of hospital admissions due to mood and psychotic disorders and to investigate whether the admission rates show variation according to the seasonal daylength (photoperiods). Patients and Methods A retrospective nationwide register-based cohort of all psychiatric admissions (N=978,079) during 1987–2017 in Finland was utilized. The smoothed time-series of adjusted ratio of observed and expected (O/E) daily counts were estimated to examine seasonal variation. The mean O/E with 95% confidence intervals (CI) was used to study the admission rates by photoperiods. The calendar days were classified into the 71-day photoperiods based on the daylength (long/summer, short/winter, equal/spring, equal/fall) and the pace of change in daylength (slowly/rapidly increasing/decreasing daylength). Results Manic episodes peaked in summer during the long (mean O/E=1.10, 95% CI=1.06–1.13) and slowly decreasing (1.09, 1.06–1.13) photoperiods and had a nadir in winter during the slowly increasing (0.93, 0.89–0.98) photoperiod. Admissions for unipolar depressive (UPD) episodes peaked in autumn and in spring at the end of the rapidly decreasing (1.03, 1.02–1.04) and increasing (1.03, 1.01–1.04) photoperiod, and dropped in summer during the long and slowly decreasing (0.95, 0.94–0.96) photoperiods. Bipolar depressive (BPD) and mixed episodes signaled excess admissions in autumn and in spring. Admissions for schizophrenia were higher than expected from summer to early-autumn, during the long and slowly decreasing photoperiods (1.02, 1.02–1.03), and lower than expected in other seasons, especially in mid-spring during the rapidly increasing photoperiod (0.98, 0.98–0.99). Conclusion The study indicates the seasonality and photoperiodicity of mental disorders, especially for manic episodes. The seasonal pattern is similar between schizophrenia and manic episodes, and between UPD, BPD, and mixed episodes.

Seasonal patterns of sickness absence due to diagnosed mental disorders: a nationwide 12-year register linkage study

“…Along with the rapidly increasing photoperiod, we found a peak in the overall diagnosis of unipolar depression in April. This overall finding of a spring peak is in line with the results of previous studies of hospital admissions (Dominiak et al, 2015;Fellinger et al, 2022;T ö rmälehto et al, 2022) and suicides (Yu et al, 2020). The explanation for this paradox may be that the abruptly and rapidly increasing light exposure after the cloudy and dark period of the year, especially at northern latitudes, acts as a trigger for depressive feelings, which deepen among those who are already depressed (Partonen et al, 2004), whereas longer-term exposure to light during the summer enhances mood in general (Papadopoulos et al, 2005;Vyssoki et al, 2014).…”

“…We observed lower absence rates than expected after the summer solstice, which continued from July to September. These findings corroborate previous research findings that have shown that clinically defined depressive disorders (Overland et al, 2019;Patten et al, 2017), hospital admission due to depressive disorders (Dominiak et al, 2015;Fellinger et al, 2022;T ö rmälehto et al, 2022) and initiation of antidepressant medication (Gardardsdottir et al, 2010) follow a seasonal pattern. However, according to a review, several studies have also failed to show such seasonal patterns (Overland et al, 2019).…”

“…As previously, the diagnosis at the highest level of the hierarchy was chosen as the primary diagnosis of the merged episode (Törmälehto et al. , 2022 ). Unipolar depressive episodes were denoted as bipolar depressive episodes if there was any history of unipolar manic or bipolar disorder in the register.…”

“…Seasonal trends in sickness absence can provide important information on the burden of mental disorders and provide answers to questions, such as how the rates vary during the year, and how healthcare services and organizations could prepare their functions accordingly. Furthermore, it is unknown whether seasonal variation in sickness absence corroborates with the previously observed seasonality of psychiatric morbidity measured by hospital admissions and healthcare use (Dominiak et al., 2015;Fellinger et al, 2022;Geoffroy et al, 2014;Overland et al, 2019;Rosenthal et al, 2020;T ö rmälehto et al, 2022;Zhang et al, 2021) as well as survey-and interviewbased data (Friborg et al, 2012;Geoffroy et al, 2014;Johnsen et al, 2012;Lobello and Mehta, 2019;Overland et al, 2019;Patten et al, 2017;Putilov, 2017;Sivertsen et al, 2021;Winthorst et al, 2011). Conditions that require hospital treatment are at the most severe end of the disease continuum.…”

“…, 2020 ; Törmälehto et al. , 2022 ; Zhang et al. , 2021 ) as well as survey- and interview-based data (Friborg et al.…”