Early Signs of Alzheimer's: The Link Between Sense of Smell and Cognitive Decline

2023-07-31 17:45:00

By Melanie Hoffmann, Medical Editor | July 31, 2023 at 7:45 p.m

Recognizing signs of Alzheimer’s disease as early as possible means that treatment can be started quickly. This is the key to keeping the disease – for which there is no cure – in check for as long as possible and slowing down its progression. A new study now points to a possible early symptom that, at first glance, one would probably not immediately associate with dementia. Medical editor Melanie Hoffmann explains the findings of the study.

When you think of symptoms of Alzheimer’s, examples like memory lapses, confusion or disorientation probably come to mind. But the sensory organs are also increasingly becoming the focus of research. For example, studies indicated B. pointed out that hearing loss can increase the risk of dementia (FITBOOK reported).1 The new study now confirmed a connection between impairments of the sense of smell, including the loss of smell, and later Alzheimer’s disease.

The Study

For their study, scientists from the University of Chicago (USA) analyzed data from 865 participants NSHAP, a representative national study on healthy aging. Among the information collected about the elderly subjects living at home was the sense of smell. This included both odor sensitivity and odor recognition. The former means the ability to perceive an odor. The second term refers to the ability to recognize and name a perceived odor. With the help of valid tests, the researchers determined the odor sensitivity of the subjects in 2010 and 2015, and odor recognition in 2005, 2010 and 2015.

In the years 2010 and 2015, measurements of the cognitive state (thinking and memory) were also carried out. The genotyping of the DNA samples also collected in 2010 made it possible to identify carriers and non-carriers of the “Alzheimer’s gene” APOE4. Statistical methods allowed the scientists to identify a possible association between APOE4, olfactory sensitivity, odor recognition and cognition.2

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Alzheimer gene, smell and cognition

Analysis of the data showed that carriers of the APOE4 gene were 37 percent less likely to have a good sense of smell than non-carriers.3

Restrictions in smell perception appeared first, namely between the ages of 65 and 69, while deficits in smell identification came later – between the ages of 75 and 79. Compared to the people who did not carry the Alzheimer’s gene, the second symptom (problems with smell recognition) worsened faster in the APOE4 carriers. In contrast, the odor sensitivity of the APOE4 carriers did not decrease faster with increasing age than that of the non-carriers.

Thinking and memory skills were similar in both groups (APOE4 carriers and non-carriers) at the start of the study. However, as might be expected, the cognitive abilities of those who carried the Alzheimer’s gene declined more rapidly over time than those who did not. The situation was similar with the limitations in odor detection, which also worsened faster for the wearers.

Loss of smell as an early warning sign of Alzheimer’s

In summary, the University of Chicago study found that there appears to be a link between the ability to smell, or loss of smell, and later Alzheimer’s disease. The APOE4 gene seems to first influence the decrease in odor sensitivity and only later on odor recognition and cognitive abilities. Accordingly, it was concluded, early testing of odor sensitivity or perception could help predict future cognitive dysfunction and ultimately Alzheimer’s.

More research is needed to understand the precise link between smell and brain health. Is there a causal relationship? What requires what? Questions to which there are no answers yet.