SAD schmad: Is seasonal affective disorder a valid construct?

The underexplored presence of seasonal affective disorder in the southern hemisphere: A narrative review of the Australian literature

BACKGROUND

Seasonal Affective Disorder (SAD) is well documented in the medical literature, particularly in more northern latitudes in agreement with proposed hypotheses for SAD's pathophysiology. However, in the southern latitudes SAD's presence remains underexplored. The second largest country in the southern hemisphere is Australia. Australia has wide ranging geographical and climatic differences that are expected to support SAD's presence. The aim of this study is therefore, to establish an evidence base for SAD in Australia.

METHODS

PubMed and Google Scholar were searched for published peer-review studies focussed on, or related to SAD, winter depression or seasonal variation in mood in Australia. There were no time-period restrictions.

RESULTS

Thirteen studies were identified. Studies explored the presence/nature of SAD, contributing factors, autonomic activity, treatment, and the validity of the Seasonal Pattern Assessment Questionnaire in the Australian population. An association between changes in mood and behaviour and seasonal occurrence was clearly identified, with SAD's presence varying by location. The highest percentage of study participants with SAD in a single location was observed in Tasmania, Australia's most southern state. The findings and interpretations of the studies included in this review are subject to the number of locations assessed, the number of studies undertaken at each location and individual study limitations.

CONCLUSIONS

Ascertaining information on the prevalence and correlates of SAD in the southern hemisphere, particularly in high-risk locations could contribute to clinical literacy into the syndrome, support management practices, and promote the early identification and treatment of the disorder.

Seasonality of depressive symptoms in women but not in men: A cross-sectional study in the UK Biobank cohort

BACKGROUND

We examined whether seasonal variations in depressive symptoms occurred independently of demographic and lifestyle factors, and were related to change in day length and/or outdoor temperature.

METHODS

In a cross-sectional analysis of >150,000 participants of the UK Biobank cohort, we used the cosinor method to assess evidence of seasonality of a total depressive symptoms score and of low mood, anhedonia, tenseness and tiredness scores in women and men. Associations of depressive symptoms with day length and mean outdoor temperature were then examined.

RESULTS

Seasonality of total depressive symptom scores, anhedonia and tiredness scores was observed in women but not men, with peaks in winter. In women, increased day length was associated with reduced reporting of low mood and anhedonia, but with increased reporting of tiredness, independent of demographic and lifestyle factors. Associations with day length were not independent of the average outdoor temperature preceding assessment.

LIMITATIONS

This was a cross-sectional investigation - longitudinal studies of within-subject seasonal variation in mood are necessary. Outcome measures relied on self-report and measured only a subset of depressive symptoms.

CONCLUSION

This large, population-based study provides evidence of seasonal variation in depressive symptoms in women. Shorter days were associated with increased feelings of low mood and anhedonia in women. Clinicians should be aware of these population-level sex differences in seasonal mood variations in order to aid recognition and treatment of depression and subclinical depressive symptoms.