NEW YORK (Reuters Health) - People with seasonal affective disorder (SAD) have a sharper sense of smell than those who don't get the winter blues, a small study shows.

The findings suggest that olfactory stimulation could help boost the effectiveness of the light treatment used to treat SAD. But it's not yet clear whether this increased olfactory sensitivity is due to patients' depression--some past research has found depressed people have a sharper sense of smell--or to their response to the seasons.

People with SAD get depressed at certain times of the year, usually in the fall and winter. Debate continues on why, but whatever the cause, basking in bright light is known to lift the mood of people with SAD.

Studies have shown that removing the olfactory bulb, the structure responsible for smell, changes animals' response to seasonal shifts in light. So Dr. Teodor T. Postolache of the National Institute of Mental Health in Bethesda, Maryland, and colleagues theorized that there might be differences in the sense of smell between SAD patients and those without the disorder. Their findings are published in the December issue of the Archives of General Psychiatry.

In a study of 14 people with SAD and 16 healthy individuals, Postolache and his team found that SAD patients did indeed have a more acute sense of smell. The difference between the two groups was particularly pronounced in the summer. The researchers gauged olfactory sharpness by checking the dilution at which each person could detect the rose-like scent of a substance called phenyl ethyl alcohol, which specifically stimulates the olfactory nerve.

Studies in mammals--though not humans--have shown that the olfactory structures in the brain are linked to the suprachiasmatic nucleus of the brain's hypothalamus, the body's master timekeeper. Thus olfactory sensitivity could be tied to the timekeeper's light response, the researchers note. And areas of the brain close to where scents and emotions are processed, they point out, have been shown to be "overly active" in people with major depression.

The next step, Postolache told Reuters Health, will be to try to determine whether the increased sensitivity to smell in SAD patients is due to their depression or their "seasonality." He also plans tests to evaluate whether olfactory nerve stimulation could make light treatment more effective. This will be tough to study, Postolache noted, because it will be difficult to find a placebo for such experiments. Possible approaches, he added, would be to expose people to a scent or placebo while they were sleeping, or to an odorant diluted to a level at which it stimulates the olfactory nerve, but does not make a person conscious of smelling it.

Postolache noted that two of his patients with SAD pointed him toward the idea of studying the sense of smell in people with the condition. One patient told him that once she smelled a particular "rotten leaf odor" in the park, she knew her winter blues were lifting. Another told him she could not smell her husband in the winter, only in the summertime.

SOURCE: Archives of General Psychiatry 2002;59:1119-1122.

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