Tag: olfaction

How do the Myriad Smells of Nature Benefit Health?

Photo by Elly Johnson on Unsplash

Contact with nature can lift our well-being by affecting emotions, influencing thoughts, reducing stress and improving physical health, as shown by studies. Even brief exposure to nature can help. One well-known study found that hospital patients recovered faster if their room included a window view of a natural setting.

Knowing more about nature’s effects on our bodies could not only help our well-being, but could also improve how we care for land, preserve ecosystems and design cities, homes and parks. Yet studies on the benefits of contact with nature have typically focused primarily on how seeing nature affects us. There has been less focus on what the nose knows. That is something a group of researchers set out to change, publishing their approach in Science Advances.

“We are immersed in a world of odorants, and we have a sophisticated olfactory system that processes them, with resulting impacts on our emotions and behaviour,” said Gregory Bratman, a University of Washington assistant professor of environmental and forest sciences. “But compared to research on the benefits of seeing nature, we don’t know nearly as much about how the impacts of nature’s scents and olfactory cues affect us.”

Bratman and colleagues from around the world outline ways to expand research into how odours and scents from natural settings impact our health and well-being. The interdisciplinary group of experts in olfaction, psychology, ecology, public health, atmospheric science and other fields are based at institutions in the US., the UK, Taiwan, Germany, Poland and Cyprus.

At its core, the human sense of smell, or olfaction, is a complex chemical detection system in constant operation. The nose is packed with hundreds of olfactory receptors, which are sophisticated chemical sensors. Together, they can detect more than one trillion scents, and that information gets delivered directly to the nervous system for our minds to interpret – consciously or otherwise.

The natural world releases a steady stream of chemical compounds to keep our olfactory system busy. Plants in particular exude volatile organic compounds, or VOCs, that can persist in the air for hours or days. VOCs perform many functions for plants, such as repelling herbivores or attracting pollinators. Some researchers have studied the impact of exposures to plant VOCs on people.

“We know bits and pieces of the overall picture,” said Bratman. “But there is so much more to learn. We are proposing a framework, informed by important research from many others, on how to investigate the intimate links between olfaction, nature and human well-being.”

Nature’s smell-mediated impacts likely come through different routes, according to the authors. Some chemical compounds, including a subset of those from the invisible realm of plant VOCs, may be acting on us without our conscious knowledge. In these cases, olfactory receptors in the nose could be initiating a “subthreshold” response to molecules that people are largely unaware of. Bratman and his co-authors are calling for vastly expanded research on when, where and how these undetected biochemical processes related to natural VOCs may affect us.

Other olfactory cues are picked up consciously, but scientists still don’t fully understand all their impacts on our health and well-being. Some scents, for example, may have “universal” interpretations to humans — something that nearly always smells pleasant, like a sweet-smelling flower. Other scents are closely tied to specific memories, or have associations and interpretations that vary by culture and personal experience, as research by co-author Asifa Majid of the University of Oxford has shown.

“Understanding how olfaction mediates our relationships with the natural world and the benefits we receive from it are multi-disciplinary undertakings,” said Bratman. “It involves insights from olfactory function research, Indigenous knowledge, Western psychology, anthropology, atmospheric chemistry, forest ecology, Shinrin-yoku – or ‘forest bathing’ – neuroscience, and more.”

Investigation into the potential links between our sense of smell and positive experiences with nature includes research by co-author Cecilia Bembibre at University College London, which shows that the cultural significance of smells, including those from nature, can be passed down in communities to each new generation. Co-author Jieling Xiao at Birmingham City University has delved into the associations people have with scents in built environments and urban gardens.

Other co-authors have shown that nature leaves its signature in the very air we breathe. Forests, for example, release a complex chemical milieux into the air. Research by co-author Jonathan Williams at the Max Planck Institute for Chemistry and the Cyprus Institute shows how natural VOCs can react and mix in the atmosphere, with repercussions for olfactory environments.

The authors are also calling for more studies to investigate how human activity alters nature’s olfactory footprint — both by pollution, which can modify or destroy odorants in the air, and by reducing habitats that release beneficial scents.

“Human activity is modifying the environment so quickly in some cases that we’re learning about these benefits while we’re simultaneously making them more difficult for people to access,” said Bratman. “As research illuminates more of these links, our hope is that we can make more informed decisions about our impacts on the natural world and the volatile organic compounds that come from it. As we say in the paper, we live within the chemical contexts that nature creates. Understanding this more can contribute to human well-being and advance efforts to protect the natural world.”

Sense of Smell Loss Uneven in Elderly

Photo by Thought Catalog on Unsplash

Contrary to previously held scientific belief, the declining sense of smell in older people is not uniform, and their liking of many smells remains the same. Researchers at the University of Copenhagen reached this conclusion after examining a large group of older Danes’ and their intensity perception of common food odours.

The decline in smell has been demonstrated scientifically. Sense of smell gradually begins to decline from about the age of 55, and 75% of those over 80 show major olfactory impairment. While it was previously believed that one’s sense of smell broadly declined with increasing age, a study from the University of Copenhagen reports that certain food odours are significantly more affected than others.

Eva Honnens de Lichtenberg Broge and her fellow researchers tested the ability of older Danes to perceive everyday food odours. The researchers measured how intensely older adults perceived different food odours — as well as how much they liked the odours.

“Our study shows that the declining sense of smell among older adults is more complex than once believed. While their ability to smell fried meat, onions and mushrooms is markedly weaker, they smell orange, raspberry and vanilla just as well as younger adults. Thus, a declining sense of smell in older adults seems rather odor specific. What is really interesting is that how much you like an odour is not necessarily dependent on theintensity perception,” observed Eva Honnens de Lichtenberg Broge.

For example, liking seemed to be largely unaffected for fried meat, onions and mushrooms, despite the largest decline in intensity perception was seen for these specific odors. The ability to smell coffee declined, among other things, though they didn’t like the aroma of coffee to the same degree as younger adults.

The test subjects included 251 Danes between the ages of 60 and 98 and a younger group consisting of 92 people between the ages of 20 and 39.

Everyday food odours

Instead of using odours of chemical origin, which is commonly the procedure when testing the sense of smell, Eva Honnens de Lichtenberg Broge developed a test kit including 14 natural food odours familiar from everyday life, including bacon, onions, toast, asparagus, coffee, cinnamon, orange and vanilla. The odours, mainly made from essential oils, were presented to participants by sniffing sticks.

The food odours were chosen based upon commonly consumed foods and dishes that older people often eat and enjoy most according to meal plans and surveys from a Danish catering company that provides food for the elderly.

What’s the story?

The researchers can only speculate as to why the declining sense of smell in older adults seems to be odours specific, especially for savoury food smells and why, in some cases, liking is largely unaffected. 

“This may be due to the fact that these are common food odours in which saltiness or umami is a dominant taste element. It is widely recognised that salty is the basic taste most affected by aging. Since taste and smell are strongly associated when it comes to food, our perception of aroma may be disturbed if one’s taste perception of saltiness is impaired to begin with,” Eva Honnens de Lichtenberg Broge suggested.

Nutriton and quality of life

The researchers hope that their findings will help improve nutrition for the elderly. While the sense of smell is important for stimulating appetite and our serotonin levels as well, according to Eva Honnens de Lichtenberg Broge, their study demonstrates that the sensitivity of one’s sense of smell need not be decisive — participants’ liking of certain foods remained unchanged.

“Our results show that as long as a food odour is recognisable, its intensity will not determine whether or not you like it. So, if one wants to improve food experiences of older adults, it is more relevant to pay attention to what they enjoy eating than it is to wonder about which aromas seem weaker to them,” concluded Eva Honnens de Lichtenberg Broge.

Source: University of Copenhagen – Faculty of Science

Journal information: de Lichtenberg Broge, E.H., et al. (2021) Changes in perception and liking for everyday food odors among older adults. Food Quality and Preference. doi.org/10.1016/j.foodqual.2021.104254.