Can your sense of smell predict when you’ll die?

Movements involved in fidgeting may counteract adverse health impacts of sitting for long periods

BY measuring how worms move toward an appealing, food-like scent, researchers at the Salk Institute, United States (US), were able to predict whether the worms would be long-lived.

The finding, publishing September 22, 2015 in the journal eLife, shows how nematodes (Caenorhabditis elegans) process information about the environment and how circuits in the brain change as an animal ages.

Also, new research suggests that the movements involved in fidgeting may counteract the adverse health impacts of sitting for long periods.

In a study published today in the American Journal of Preventive Medicine, a team of researchers, co-led by the University of Leeds and University College London (UCL), report that an increased risk of mortality from sitting for long periods was only found in those who consider themselves very occasional fidgeters.

They found no increased risk of mortality from longer sitting times, compared to more active women, in those who considered themselves as moderately or very fidgety.

The study examined data from the University of Leeds’ United Kingdom (UK) Women’s Cohort Study, which is one of the largest cohort studies of diet and health of women in the UK.

An assistant professor in Salk’s Molecular Neurobiology Laboratory, Sreekanth Chalasani, said: “We’re not saying that your ability to smell is going to make you live longer. But this odor behavior is likely indicative of some kind of underlying physiology.”

The small C. elegans has 12 pairs of specialized neurons in its brain that detect stimuli in the environment. Scientists had previously identified individual pairs of these neurons as required for the animals to respond to attractive odors. Chalasani and his colleagues wanted to understand this entire process in more detail.

In their new work, the researchers measured the responses of all 24 neurons as C. elegans was exposed to benzaldehyde — a chemical that gives off a pleasant, almond-like smell. Surprisingly, rather than the individual pairs that had been previously shown, they found that additional neurons were also involved.

Interestingly, these cells were divided into primary and secondary neurons. Primary neurons showed activity in response to the benzaldehyde, while secondary neurons responded to signals sent by the primary neurons. By having a neural circuit structured like this, the team hypothesizes, the worm can get better information on the strength or concentration of a smell.

“If you have multiple different cells that are all detecting a stimulus, you can use the combination of them to get more dynamic information,” says Sarah Leinwand, a graduate student in the Chalasani lab and first author of the new paper. “Using this strategy allows an animal to generate flexible behavioral responses to its environment.”

For instance, some behaviors could only be triggered when a smell is strong enough to cause activity in particular combinations of neurons. The researchers speculate that other species with larger brains may use similarly structured neural circuits to represent sensory information and fine-tune their behaviors.

The scientists went on to show a correlation between poor performance on a smell-based test (moving toward a point source of benzaldehyde), the activity of secondary neurons and the animal’s lifespan. Older animals that were more successful in finding the odor lived about 16 per cent longer than animals that were less good at moving toward the smell.

Study co-lead author Professor Janet Cade, from the School of Food Science and Nutrition at the University of Leeds said: “While further research is needed, the findings raise questions about whether the negative associations with fidgeting, such as rudeness or lack of concentration, should persist if such simple movements are beneficial for our health.”

Even among adults who meet recommended physical activity levels and who sleep for eight hours per night, it is possible to spend the vast majority of the day (up to 15 hours) sitting down.

The study builds on growing evidence suggesting that a sedentary lifestyle is bad for your health, even if you are physically active outside work.

Breaks in sitting time have previously been shown to improve markers of good health, such as body mass index and your body’s glucose and insulin responses. But until now, no study has ever examined whether fidgeting might modify an association between sitting time and death rates.