A poor sense of smell might matter more than you thought

As one of the five major senses, you could argue that our sense of smell is the least important. Sight, hearing, touch, and taste may poll better than smell, but try telling that to someone who has lost their sense of smell entirely.

The truth is that loss of the ability to smell comes with a significant cost, because olfaction serves several purposes that affect quality of life and even safety, including

• stimulation of appetite
• enhancement of the sense of taste
• alerting you to which foods should not be eaten (if they're rotting, for example)
• warning you of danger (as with smoke warning of fire).

Loss of smell can also be a sign of illness. For example, sinus infections, sinus tumors, and neurologic diseases such as multiple sclerosis may be associated with a reduced sense of smell. Smoking leads to increased mucus production, reduced clearance of airway mucus, and damage to olfactory cells in the nose responsible for the appreciation of odors. As a result, smokers often report poor olfaction and quitters may notice improvement — one more reason to quit! Certain medications (such as the statin-lowering drug atorvastatin, the blood pressure-lowering drug amlodipine, and the antibiotic erythromycin) may also impair one's sense of smell.

About 12% of people over the age of 40 report at least some trouble with their sense of smell, and it rises with age: nearly a quarter of men in their 60s reported a diminished sense of smell.

Loss of smell may predict future illness

For years, we've known that people with a poor sense of smell have higher rates of death, Parkinson's disease, and Alzheimer's disease. The reason for this isn't clear, but one possibility is that loss of smell might be an early indication that one of these conditions is present. Or, perhaps other conditions that affect smell increase the risk of these diseases. It could also be due to medications taken to treat symptoms of these conditions. Or there may be other explanations, but the connection remains mysterious.

New research explores connections between health and sense of smell

A new study explores the relationship between loss of smell and future disease — and attempts to explain it. Researchers tested the sense of smell of nearly 2,300 elderly people and monitored their health and cognitive function over 13 years. Compared with those who had good olfaction at the start of the study, those with the worst sense of smell

• tended to smoke, drink more alcohol, be older, and be male
• were more likely to have dementia, Parkinson's disease, and kidney disease at the start
• had a 46% higher chance of death over 10 years
• had a higher risk of death due to dementia, Parkinson's disease, and cardiovascular disease in the coming years.

Interestingly, sense of smell was a stronger predictor of death in those who were healthiest at the start of the study. The higher rates of neurologic disease only explained a small part of the higher rates of death among people with poor sense of smell.

Why does this matter?

These findings are interesting and confirm those of past research. But we need to figure out what do with this information. Does a poor sense of smell mean you should have extensive testing for neurologic or cardiovascular disease? Is there a direct, causal connection between problems with smell and higher rates of death — for example, does poor smell sensation indicate the presence of a fatal disease? Or might the link be indirect, with poor smell sensation and a higher risk of death due to some other factor? The answers to these questions could lead to better screening approaches to common conditions affecting the elderly, as well as insights into how these diseases develop.

The bottom line

We need more research on the links between poor olfaction and health. Until we do, let your doctor know if you notice that your sense of smell isn't what it used to be. It doesn't mean you have a serious disease — a 2016 study found that more than three-quarters of elderly people with the poorest sense of smell had normal brain function several years later. But losing your sense of smell warrants evaluation that could turn up something important — and possibly reversible.