We cover a large study that linked sense of smell and dementia, but this isn't a reason to worry that it is caused by dementia.
A study of nearly 3,000 people in the US found that older adults with a poor sense of smell were more likely to develop dementia later in life. Although the link between smell and dementia risk is an important finding, there are some key questions we need to answer.
First, if someone fails the test, how likely are they to develop dementia? Despite the fact that risk of dementia was greater in people with poor sense of smell, only nine in 100 people who failed the test would be expected to get a dementia diagnosis within five years. This reflects the fact that it’s common for people to experience changes to their senses, and people shouldn’t worry that this is an early sign of dementia.
Second, if someone passes the test, how likely are they to develop dementia? The test has a clearer answer to this question, as 97 out of 100 people who pass the test won’t develop dementia. So it seems that this test is more useful for telling us who won’t develop dementia than who will.
In practice, no single test can diagnose dementia. Doctors use a range of different examinations; the strengths and weaknesses of new tests need to be compared to existing methods to understand where improvements can be made.