Seasonality and symptoms of depression: A systematic review of the literature.

Simon Øverland,Wojtek Woicik,Ian Colman,Hans Heli,Lindsey Sikora,Børge Sivertsen,Kristoffer Whittaker,Fritjof Stein Skjelkvåle

doi:10.1017/s2045796019000209

Abstract

Lay opinions and published papers alike suggest mood varies with the seasons, commonly framed as higher rates of depression mood in winter. Memory and confirmation bias may have influenced previous studies. We therefore systematically searched for and reviewed studies on the topic, but excluded study designs where explicit referrals to seasonality were included in questions, interviews or data collection. Systematic literature search in Cochrane database, DARE, Medline, Embase, PsychINFO and CINAHL, reporting according to the PRISMA framework, and study quality assessment using the Newcastle-Ottawa scale. Two authors independently assessed each study for inclusion and quality assessment. Due to large heterogeneity, we used a descriptive review of the studies. Among the 41 included studies, there was great heterogeneity in regards to included symptoms and disorder definitions, operationalisation and measurement. We also observed important heterogeneity in how definitions of 'seasons' as well as study design, reporting and quality. This heterogeneity precluded meta-analysis and publication bias analysis. Thirteen of the studies suggested more depression in winter. The remaining studies suggested no seasonal pattern, seasonality outside winter, or inconclusive results. The results of this review suggest that the research field of seasonal variations in mood disorders is fragmented, and important questions remain unanswered. There is some support for seasonal variation in clinical depression, but our results contest a general population shift towards lower mood and more sub-threshold symptoms at regular intervals throughout the year. We suggest future research on this issue should be aware of potential bias by design and take into account other biological and behavioural seasonal changes that may nullify or exacerbate any impact on mood.

Highlights

Depression is common (Waraich et al, 2004) with reported 1-year prevalence estimates ranging around 6.6% in the USA (Kessler et al, 2003), 5.5% in Canada (Patten et al, 2015), 7.4% in Finland (Markkula et al, 2015) and is associated with significant disease burden worldwide (Whiteford et al, 2015)
For the purpose of this paper, we focused on depression and depressive symptoms, and hospital admissions and prescriptions related to depression
Another four papers were added after an updated literature search, and a total of six studies were identified through other papers and included

Summary

Introduction

Depression is common (Waraich et al, 2004) with reported 1-year prevalence estimates ranging around 6.6% in the USA (Kessler et al, 2003), 5.5% in Canada (Patten et al, 2015), 7.4% in Finland (Markkula et al, 2015) and is associated with significant disease burden worldwide (Whiteford et al, 2015). A host of single studies suggest potential risk factors for depression may vary with seasons (Rosenthal et al, 1984; Roecklein and Rohan, 2005). Sleep patterns (Rosenthal et al, 1984; Lewy et al, 1987), levels of physical activity (Shephard and Aoyagi, 2009), reproductive behaviours (Roenneberg and Aschoff, 1990; Bronson, 1995), a host of neurobiological factors (Carlsson et al, 1980; Kivela et al, 1988; Avery et al, 1997; Neumeister et al, 2000; Lambert et al, 2002; Morera and Abreu, 2006; Kalbitzer et al, 2010; Abell et al, 2016) are reported to co-vary with seasonal variation and might impact on mood. The extent of this impact, and whether or not it translates to functional and clinical significance, remains controversial

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Discussion

Conclusion