Bryan S. Cobb, Jess G. Fiedorowicz, M.D., Ph.D

For most of us, the term “seasonal affective disorder” – with the apt acronym SAD – likely evokes thoughts of winter blues, of energy and interest levels that fall along with the snowflakes and a rut that only deepens as the days shorten.  Indeed, early studies on SAD, including the 1984 article by Rosenthal et al., in which the term was coined, reported a higher incidence and or worsening of symptoms at higher latitudes [1, 2], where winter days are typically shorter.  Young et al. even showed that variation in risk of SAD across latitudes & days of the year can be accounted for by differing photoperiods, simply defined as the time between sun-up and sun-down [3].  Biological evidence, such as an association between winter lowering of mood and circadian phase delay [4], further supports the theory of a SAD-shorter day link.
 
There are, however, several deficiencies with this conception of SAD and its causes. Multiple reviews have cast doubt on the definiteness of latitudinal effects, especially across different countries [5, 6], and Young et al.’s analysis indicated that photoperiod explained just over one-quarter of the variance in SAD risk [3].  Even more problematic for the photoperiod hypothesis is the observation that some experience summer, not winter, worsening of mood.  Factors beyond a dearth of daylight must be at work.

As illuminated in a study by Kasof, one such determinant of SAD risk and presentation pattern is a patient’s cultural backdrop [7].  Kasof notes that while Westerners experience greater negative affect with shorter photoperiods (i.e., winter time), responses tend to be the opposite in non-Western nations, with lower moods in the summer. Interestingly, this not only applies to affect but to such socially-salient indicators as stock market returns.

In attempt to explain this trend through meta-analysis of aggregate data (41 studies from 18 countries), Kasof correlated each countries’ seasonal pattern of SAD with its ratings on individualism-collectivism and power distance (PD) scales.  The ratio of summer SAD to winter SAD was greater in countries with high collectivism and PD, which is basically a measure of respect, perceived separation from authority, and preference for autocratic leadership [7].  These relationships persisted after controlling for potential study-level confounds including sex ratio, median age, study response rate, method or season of assessment, mean summer temperature and mean winter photoperiod.  The latter two factors are of particular interest because countries closer to the equator – with hotter summer days and longer winter photoperiods – are typically more collectivistic and higher in PD.

This novel association may illuminate otherwise unexplained findings such as those by Avasthi et al. from an Indian outpatient psychiatric clinic in which the majority of patients diagnosed with SAD had symptoms begin in summer or spring [8].  According to the cultural rating scales utilized by Kasof [9], India has among the highest PD scores of any nation.  India would thus be expected to have a higher proportion of summer SAD sufferers, based on the hypothesis generated by Kasof’s ecological data.  Additionally, Kasof notes that higher individualism scores in younger generations may partially underlie the observed trend toward more winter SAD in this population.

If confirmed, these findings could improve how we conceptualize SAD.  Studies such as this also serve to remind us of an under-emphasized side of medicine – the social environment in which a patient’s biology and psychology interact.  Effective diagnosis and disease management necessitates understanding of this social and cultural milieu.

 
References
1.    Rosenthal, N.E., et al., Seasonal affective disorder. A description of the syndrome and preliminary findings with light therapy. Arch Gen Psychiatry, 1984. 41(1): p. 72-80.
2.    Rosen, L.N., et al., Prevalence of seasonal affective disorder at four latitudes. Psychiatry Res, 1990. 31(2): p. 131-44.
3.    Young, M.A., et al., Which environmental variables are related to the onset of seasonal affective disorder? J Abnorm Psychol, 1997. 106(4): p. 554-62.
4.    Murray, G., N.B. Allen, and J. Trinder, Seasonality and circadian phase delay: prospective evidence that winter lowering of mood is associated with a shift towards Eveningness. J Affect Disord, 2003. 76(1-3): p. 15-22.
5.    Magnusson, A., An overview of epidemiological studies on seasonal affective disorder. Acta Psychiatr Scand, 2000. 101(3): p. 176-84.
6.    Mersch, P.P., et al., Seasonal affective disorder and latitude: a review of the literature. J Affect Disord, 1999. 53(1): p. 35-48.
7.    Kasof, J., Cultural variation in seasonal depression: cross-national differences in winter versus summer patterns of seasonal affective disorder. J Affect Disord, 2009. 115(1-2): p. 79-86.
8.    Avasthi, A., et al., Seasonality in affective disorders using SPAQ. Indian J Psychiatry, 2003. 45(3): p. 166-73.
9.    Hofstede, G.H., Culture’s Consequences. 2 ed. 2001, Beverly Hills, CA: Sage Publications. 596.