A magazine for friends of the Warren Alpert Medical School of Brown University.

Odors by the Hours


Smell sensitivity varies with circadian rhythm, study suggests.

It has always been apparent that some individuals have a better sense of smell than others, but a new study of 37 teens provides the first direct evidence that within each person, smell sensitivity varies over the course of each day. The pattern, according to the data, tracks with the body’s internal day-night cycle, or circadian rhythm.

“This finding is very important for olfactory perception science,” says Rachel Herz, PhD, lead author of the study in Chemical Senses and an adjunct assistant professor of psychiatry and human behavior. “This hadn’t been known before and this is the first clear, direct evidence.”

As one of the five senses, smell is an important ability, Herz says, not only for experiencing and enjoying the world, but also for receiving information about danger, such as nearby fire or spoiled food, and for basic functions like eating. Changes in the sense during the day can affect all these capabilities.

Herz, an expert in the sense of smell, made the findings in collaboration with sleep expert Mary Carskadon, PhD, a professor of psychiatry and human behavior. Carskadon is conducting a larger study with a hypothesis that circadian timing and sleep habits may affect the eating habits of teens, potentially contributing to obesity.

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