Research report
An examination of seasonality experienced by Australians living in a continental temperate climate zone

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Abstract

Background: To date, there has been only limited information on factors associated with seasonal changes in mood and behaviour experienced by a random sample of Australians living in a continental temperate climate region. This paper identifies socio-demographic, psychological and personality factors associated with reporting higher levels of seasonality. Method: Information on seasonal change using the Seasonal Pattern Assessment Questionnaire (SPAQ) was obtained from 7485 persons in three age groups. Age and sex differences in seasonality scores were examined. Those meeting probable caseness for seasonal affective disorder were identified and compared with less-seasonal participants on a range of state and trait measures. Results: Levels of seasonality reported by survey participants were comparable to those reported in northern hemisphere studies of randomly selected community samples. However, these levels were significantly lower than other key studies outside Australia and previous Australian findings. Compared with less-seasonal participants, those reporting seasonal change had more current depressive and anxiety symptoms and higher levels of negative affect, regardless of season of interview. Limitations: This study is likely to over-estimate the number of participants who meet requirements for caseness for seasonal affective disorder. Conclusion: Levels of seasonality experienced by a random sample of Australians living in a temperate climate are comparable to those reported by similar groups in the northern hemisphere. Importantly, this study found that those experiencing higher levels of seasonality had significantly more current depressive symptoms than less-seasonal participants across all seasons. These results raise questions about the usefulness of the SPAQ as a measure of seasonal variation in mood and behaviour.

Introduction

It has long been recognised that changes in seasons may affect an individual’s mood and behaviour. In 1984, Rosenthal and colleagues described seasonal affective disorder (SAD): clinical depression occurring regularly during winter months and remitting by the following spring or summer. They also identified a range of behavioural and physiological changes reported by individuals during periods of winter depression including decreased physical activity, changes in appetite, increased drowsiness, decreased sociability and increased irritability and suspiciousness (Rosenthal et al., 1984).

An instrument developed by Rosenthal, the Seasonal Pattern Assessment Questionnaire (SPAQ), has been widely used to measure individuals’ seasonal mood and behaviour changes (Thompson et al., 1988). Magnusson (2000) has provided a comprehensive overview of epidemiological findings on this topic. While a summer pattern of seasonality has been identified (Boyce and Parker, 1988, Morrisey et al., 1996), most research has focused on winter seasonality experienced by individuals living in temperate or cold climate areas of the northern hemisphere. Primary factors affecting winter-based SPAQ scores are sex and age. Women of reproductive age are at highest risk with that risk declining with age. Men report low levels of winter-based seasonality that typically do not vary across the life-span (Kasper et al., 1989, Muscettola et al., 1995). Other research has identified that this sex difference does not hold for summer-based seasonality (Morrisey et al., 1996, Rohan and Sigmon, 2000). Associations have also been found between seasonality and biological factors including retinal sensitivity (Hebet et al., 2002), and genetic factors (Jang et al., 1998, Johansson et al., 2001, Madden et al., 1996). Psychological measures, including neuroticism and environmental factors such as season of interview, have been associated with seasonal mood change, although these findings are inconsistent (Gordon et al., 1999, Jang et al., 1997, Lund and Hansen, 2001, Murray et al., 1995, Murray and Hay, 1997). Similarly, findings concerning the impact of latitude on seasonal change are inconsistent. Rosen et al. (1990) found that those at higher latitudes in North America reported more seasonality, although this finding has not been replicated in other countries (Muscettola et al., 1995, Murray and Hay, 1997). Associations between seasonality and other factors, including education and income level, have been reported but remain unexplained (Blazer et al., 1998, Saarijarvi et al., 1999). It has also been argued that genetic adaptation may have assisted some populations (for example, Finns) to adapt to colder climates, thereby reducing the impact of winter on their mood and behaviour (Saarijarvi et al., 1999).

A few studies on the effects of seasonal change have been undertaken in the southern hemisphere. Six of these have been conducted in Australia (Boyce and Parker, 1988, Madden et al., 1996, Morrisey et al., 1996, Murray et al., 1995, Murray et al., 2001, Murray and Hay, 1997). Table 1 summarises the results of this Australian-based research. Each of these studies improves understanding of seasonal changes in mood and behaviour experienced in the southern hemisphere. However, they also have some limitations in clarifying the level of, and demographic and personal attributes associated with, seasonality as reported by healthy individuals living in a temperate climate region in Australia. In one case, the method of selecting participants ensured that they were likely to have experience of this condition (Boyce and Parker, 1988). Morrisey et al. (1996) found individuals living in the tropics to be more likely to report summer-based changes in mood and behaviour. The remaining studies included only women in their samples (Murray et al., 1995, Murray and Hay, 1997), did not address the relationship between sex and seasonality (Madden et al., 1996, Murray et al., 2001), or drew participants from a wide range of latitudes (Madden et al., 1996, Murray et al., 1995, Murray and Hay, 1997). These studies also provide only limited information on the impact of age on seasonality experienced by Australians.

This paper reports analyses of the attributes of Australians living in a temperate climate who experience seasonal changes in mood and behaviour. These analyses provide useful information on the similarities and differences between seasonality experienced in the northern and southern hemispheres. This analysis drew on data from the PATH Through Life Project, a community-based study of 7485 individuals from three age groups, conducted by the Centre for Mental Health Research in Canberra, Australia. The region in which PATH participants lived is at latitude 35° south, 106 km inland, 560 m above sea level, and experiences warm summers and cold winters. Average monthly maximum temperatures range from 11.5 °C in July to 28.5 °C in January, and average monthly minima 0.0 (July) to 13.8 °C (February) (Bureau of Meteorology, 2002). Rainfall is distributed evenly throughout the year and averages 633 mm annually (Bureau of Meteorology, 2002). Compared with most other major metropolitan areas located on the Australian coastline, the region experiences colder winters and less humid summers.

Information obtained from PATH participants included demographic, psychological and physical health measures as well as components of the SPAQ. Analyses of data obtained from this sample could identify attributes associated with experiencing seasonal changes after controlling for factors that have been found to affect this measure including latitude and season of interview.

Section snippets

Method

The PATH Through Life Project is a longitudinal survey of residents living in Canberra and the neighbouring town of Queanbeyan, New South Wales. Participants comprise three age groups: those aged 20–24 years on 1 January, 1999; those aged 40–44 years on 1 January 2000; and those aged 60–64 years on 1 January 2001. Sampling frames for this survey were the Electoral Rolls for Canberra and Queanbeyan, Australia. Enrolment is compulsory for Australian citizens. For the first two age cohorts, the

Results

We first identified the extent and type of seasonality reported by participants and calculated mean GSS for all participants and for age and sex sub-groups (Table 2). Some findings from other comparable research are provided in Table 3. As expected, higher seasonality scores were reported by women (t[7429]=12.29, P<0.001) and younger participants (F[2,7428]=430.55, P<0.001). There was also a significant age-by-sex interaction.

When all age groups were combined, 3839 participants (51.3%) reported

Discussion

This study examined levels of seasonality reported by participants in a large community-based survey. Levels of seasonality here were comparable with those reported in some northern hemisphere-based community studies, but significantly lower than those reported in other, comparable research, particularly that by Kasper et al. (1989). Further, seasonality scores reported in this Canberra-based study are significantly lower than those reported for Australians in other locations (Table 3). The

Conclusion

Levels of seasonality experienced by a random sample of Australians living in temperate climate zone are comparable to those reported by similarly drawn community groups in the northern hemisphere. Younger adults experienced higher levels of seasonality compared with their older counterparts. This study found that those who perceived themselves to be most affected by seasonal change had higher levels of neuroticism and lower levels of mastery. Further, those experiencing high levels of seasonal

Acknowledgements

We wish to thank Helen Christensen, Karen Maxwell and the team of Centre for Mental Health Research interviewers for their assistance with this study. Funding was provided by Program Grant No. 179805 from the National Health and Medical Research Council.

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