Catering for the elderly: the decline of smell and taste

In order to ensure that the elderly receive a healthy diet that is also appealing, it is important to understand the changes in their perceptions of smell and taste, which can lead to a decline in appetite and meal enjoyment and, eventually, to malnutrition.

A team headed by Claire Sulmont-Rossé from the National Institute for Agricultural Research (INRA) in Dijon, France, a member of the European Sensory Network (ESN), has put the sensory abilities of the elderly under the magnifying glass, investigating the senses of smell and taste of 559 people between the ages of 65 and 99.

Large individual differences

Studies over the last 25 years have shown that the sense of smell, and to a lesser extent the sense of taste, decline in the elderly. However, there exists a large variability in the elderly population.

Do the senses of taste and smell decrease to the same extent? Which aspects of odour perception are especially affected in the elderly? Which aspects are dependent on the person’s age?

The test series

To answer these questions, Claire Sulmont-Rossé and her team invited volunteers from four separate regions of France. The seniors participated in a series of tests that explored various aspects of their sense of smell and taste. They also answered questions concerning their living situation. Sulmont-Rossé explained, “We didn’t just want to single out a particular olfactory capacity, such as the odour threshold; we wanted to obtain an overall picture of the sense of smell. For this we used tests that showed how well a participant could perceive, differentiate and categorise the smells. It is quite possible that specific ageing processes govern these various olfactory abilities differently.”

Using a set of chemosensory tests, the researchers assessed the ability of the participants to detect odours at a small concentration, to discriminate between different odour qualities (for instance, discriminate between a beef odour and a fish odour) and to determine whether an odour is a food odour (strawberry, caramel) or a non-food odour (rose, perfume). Finally, the researchers used rising concentrations of salt solutions to determine the participants’ thresholds in perceiving and identifying the taste of salt, which is acknowledged to be more affected by ageing than the other tastes.

Four groups discovered

“We were somewhat surprised by the results,” said Claire Sulmont-Rossé. “With 40% of the seniors, the sense of smell and taste was only very slightly impaired.”

In their analysis, the researchers detected four different sensory clusters:

Cluster 1: Good sense of smell and taste (well-preserved chemosensory abilities)

43% of the seniors had a well-preserved sense of smell and taste. However, with the exception of salt detection, they did not do as well as a parallel group of 63 participants with a mean age of 28.

Cluster 2: Good sense of sense of smell but heavily impaired sense of taste (strong gustatory impairment)

33% of the participants had a well-preserved sense of smell but had lost a high degree of their sense of taste.

Cluster 3: Impaired sense of smell and taste (chemosensory impaired)

21% of the participants showed moderate impairment to both smell and taste. However, their sense of taste was still better than that of group 2.

Cluster 4: Strongly impaired sense of smell

Only 3% of the test subjects had lost most of their sense of smell and were unable to differentiate and categorise the various smells. Nevertheless, their sense of taste was less impaired than in cluster 2.

In general, the participants in cluster 1 were younger, did not take medication that would affect their sense of smell and taste, and were able to take care of their daily needs without help. Participants in clusters 3 and 4 were older as a rule, took medication that affected their sense of smell and taste, and needed help, either in their own homes or as residents of a facility for the aged. In terms of measured variables, cluster 2 did not stand out from the other clusters.

Smell and taste age independently

As expected, the research team found a correlation between the results of the various smell tests as well as a correlation between the results of the taste tests. However, the scientists did not find a correlation between the scores of the smell and taste tests. This suggests that the two sensory systems are affected by the ageing process independently from one another.

Why do the senses of smell and taste function separately from one another? Possibly each system reacts independently to the ageing process and such environmental influences as pollution. Claire Sulmont explained, “The olfactory neurons are in direct contact with the external environment. Thus they are more likely to be influenced by aggressive environmental factors than are gustatory cells.”

Food products conform to the target groups

Several physiological processes, such as drying of the olfactory mucosa, decrease in saliva flow and reduction in the number of sensory receptors, have been reported to play a role in the decline of sensory perception. However, results of the study strengthen the hypothesis that the diminishing of chemosensory abilities is not only caused by classic processes of physical ageing; rather, the events that usually accompany ageing play a major role. Health problems, dental disease and the use of particular types of medication can be contributing factors. Claire Sulmont-Rossé stated, “It appears that age per se influences the perception of low-intensity odour and taste stimuli. However, factors associated with a senior’s health status seem to have a negative influence on their ability to perceive even high-intensity chemosensory stimuli.”

How might the food industry and the institutions that care for the elderly benefit from these findings? “To be sure that people of every age group will enjoy their food, the key drivers for food choices should be ascertained in conjunction with the chemosensory abilities of the consumer,” Clair Sulmont-Rossé emphasised. “For instance, the visual aspects and texture of food could be modified so that people with a diminished sense of smell could have more enjoyment eating.”

Image credit: ©iStockphoto.com/Pamela Moore