Previous studies have shown that removing the olfactory bulb – a structure in the limbic region of the brain that is responsible for smell – changes animals’ response to seasonal shifts in light.

In addition, areas of the brain close to where scents and emotions are processed have been shown to be overly active in people suffering from major depression.

With this background in mind, Dr Teodar Postolache from the National Institutes of Health in Bethesda, Maryland – and colleagues from other institutions – sought to determine whether differences exist in the sense of smell between patients with SAD and those without the disorder.

The researchers examined 14 people with SAD and 16 healthy volunteers, once in the winter and once in the subsequent summer. Olfactory sharpness was assessed by checking the dilution at which each person could detect the rose-like scent of a chemical called phenyl ethyl alcohol.

The team found that patients with SAD had significantly lower odor detection thresholds than the controls. The difference between the groups was more pronounced during the summer, but not significantly so.

Writing in the journal Archives of General Psychiatry, the team speculate that olfactory stimulation might help enhance the effectiveness of the light treatment used to treat SAD.

“Although light treatment in winter is effective, it does not make patients with SAD feel as well as they do in summer,” they explain.

The researchers conclude that further studies are needed to determine whether this increased olfactory sensitivity is due to the patients’ depression or to their response to the seasons.

Reference: Postolache et al, Archives of General Psychiatry 2002;59:1119-1122

© HMG Worldwide 2002
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