Aging and the Chemical Senses

Everyone is aware that the visual and auditory senses dim with age, and expects the elderly to need reading glasses and hearing aids. What about the chemical senses of smell and taste? In what ways do our perceptions of the volatile and water-soluble molecules we smell and taste change? How pronounced is that change? And how early in life does it begin? Before addressing these questions, it is important to recognize that smell (olfaction) and taste (gustation) are distinct physiological systems. They have different receptor types and peripheral neural pathways, and they respond, by and large, to different types of chemical stimuli. On the other hand, brain responses to many smell and taste stimuli overlap. Thus, when food is eaten—simultaneously releasing some molecules that stimulate taste receptors in the oral cavity and some that flow through the throat to the nose and stimulate olfactory receptors—it is perceptually very difficult to distinguish which components of the resulting flavor perception are smells and which are tastes. In fact, however, research at Monell and other institutions has shown that these two aspects of food flavors are not equally affected by ageing: diminutions in olfactory sensitivity are more pronounced than diminutions in gustatory sensitivity.