Seasonal Affective Disorder and HPA Axis Disturbance

Seasonal affective disorder (SAD) is known as a form of depression that usually occurs in the winter, with hyperphagia and a craving for carbohydrate-rich foods and weight gain observed in these depressive episodes [1] [2]. It therefore seemed highly likely that the correlation between leptin levels in individuals with SAD was altered, which was the topic of interest in the study referred to here. However, no change of leptin levels according to season was detected in persons with known SAD compared to the control group, whereas increased appetite and weight gain were present [1].

As mentioned in the article, this may be due to a change in the highly pulsatile circadian secretion of leptin, which was not measured in the study. A strong indicator that leptin levels are linked to SAD is that leptin levels are significantly higher in women [1], as is the prevalence of SAD itself [3]. A more far-reaching disturbance at HPA axis level not only incorporating leptin, but also several transmitters known to play a crucial role in the regulation of appetite such as ghrelin and neuropeptide Y would seem far more likely. Melatonin would be a particularly interesting candidate, as its secretion is known to be highly dependent on light exposure, which is apparently an important factor in SAD since it occurs typically in the “darker” periods of the year and it is more prevalent at higher rather than lower latitudes [4]. Another interesting finding is that leptin levels in sportsmen and sportswomen may reach as low as a third of levels in normal individuals, so the effects of physical exercise [5] - typically performed more intensively in the spring and summer months - also seem to be involved in the regulation of leptin.

For further investigation, a broader view on the HPA axis may prove useful in understanding the pathogenesis of SAD.

References

• 1 Cizza G, Romagni P, Lotsikas A, Lam G, Rosenthal N E, Chrousos G P. Plasma leptin in men and women with seasonal affective disorder and in healthy matched controls.  Horm Metab Res. 2005;  37 45-48
• 2 Krauchi K, Reich S, Wirz-Justice A. Eating style in seasonal affective disorder: who will gain weight in winter?.  Compr Psychiatry. 1997;  38 80-87
• 3 Magnusson A, Boivin D. Seasonal affective disorder: an overview.  Chronobiol Int. 2003;  20 189-207
• 4 Miller A L. Epidemiology, etiology, and natural treatment of seasonal affective disorder.  Altern Med Rev. 2005;  10 5-13
• 5 Popovic V, Duntas L H. Leptin TRH and ghrelin: influence on energy homeostasis at rest and during exercise.  Horm Metab Res. 2005;  37 533-537