Country air could be good for us because it’s slightly poisonous

11 Jul

just looking out of a window on to a natural scene
helped patients recover more quickly after surgery than those whose
view was of a brick wall.

Smell the difference

More recently, a UK study showed that people who live in coastal
locations take significantly more exercise than those inland. And a
Japanese study on physiological effects of shinrin-yoku – literally
“forest bathing” – found that participants had lower blood pressure
and lower levels of the stress hormone cortisol when they took
country walks than when they walked city streets.

These are not the only ways in which the countryside could impact
our health. Graham Rook of University College London argues that
blue-green space improves the regulation of our immune system,
because it exposes us to bacteria and parasites with which we
co-evolved. I have a new theory to add to the mix: the country and
sea air is good for us because it is slightly poisonous.

Take a stroll by the ocean or in the woods, and you can smell the
difference compared to a town or city. It’s more than just a lack of
pollution. What you are sensing is an airborne plethora of particles
and chemicals produced by plants, fungi and bacteria.

Wave action produces microscopic droplets of seawater, bringing with
them compounds from marine cyanobacteria, algae and seaweed. The
presence of these biomolecules in the atmosphere represents a
radical departure from the urban environment, which is more likely
to contain synthetic pollutants and mildew.

Of particular interest to me are compounds called phytochemicals,
derived from plants, algae and cyanobacteria. Some of these are
polyphenols – antioxidants which often act as natural defences
against pathogens and predators. Others are volatile terpenoids,
which are responsible for the scents of plants. What is so special
about these chemicals?

When I came across the concept of biophilia 10 years ago, I wondered
if chemical factors in the environment might be responsible for the
beneficial effects of nature. I now think that breathing in and
ingesting these natural chemicals may have a positive effect on our
physiology. They may even be able to block the progression of many
diseases such as diabetes and cancer, as well as certain
neurodegenerative processes (Environmental Research, vol 140, p 65).

During the course of human evolution our ancestors were exposed to a
legion of phytochemicals, through inhalation and their diet. Though
many of these are toxic at high concentrations, this long-standing
exposure made us tolerant to low doses. In fact, exposure to low
levels of these toxins can be of benefit due the mild stress they
induce, which triggers repair mechanisms and enhances tolerance to
bigger doses – an effect known as hormesis.

Abundant evidence exists that dietary phytochemicals have this
beneficial hormetic effect, particularly the antioxidants found in
many vegetables, fruits and medicinal plants. If eating food
containing these substances is good for us, such as in the
Mediterranean-style diet, then ingesting them via an airborne route
may also be beneficial.

How exactly could these chemicals boost health? By inhibiting an
important system, the mTOR pathway, that controls many aspects of
cell function and growth.

When this signalling system is overactive, it can lead to diabetes,
inflammation, certain cancers and neurodegeneration. Inhibiting the
mTOR pathway activates a number of protective systems such as tumour
suppression and autophagy – the destruction of damaged cellular
components, allowing new ones to form.

Some phytochemicals also appear to have biological effects similar
to those of severe calorie restriction, which inhibits mTOR and has
been shown to have health benefits for humans and increase lifespan
in many animal species.

And mTOR may not be the only cell-signalling pathway targeted by
these airborne molecules. Phytochemicals in food can influence other
systems, such as the MAPK/ERK pathway which plays a key part in
cancer progression, and AMPK, a protein which monitors the energy
level of cells.

This “biogenics” hypothesis remains untested at the moment. It is
uncertain whether the levels of bioactive chemicals in natural
aerosols are sufficient to influence cell signalling, although my
colleagues at the University of Exeter and I plan to study the
effects of low concentrations of phytochemicals in mice. However, we
already know that certain airborne phytochemicals can interact with
cell signalling pathways to cause hypersensitivity in the immune
system – giving rise to hay fever, for example – and that minute
amounts of airborne algal toxins can induce asthma.

Planners are putting increasing emphasis on creating urban parks as
ever more people move to the city from the country. But maybe there
are other ways to bring the country to the city.

If it turns out that airborne natural molecules do indeed boost our
health, then this leads to the question of whether we could “bottle”
the benefits of country and seaside air. Natural phytochemicals
could be added to aerosols for use in the home and in public spaces
such as shopping malls. They could even be added to our diet.

The modern built environment represents a significant change of
airborne milieu for humans. City air is not only more polluted but
lacks the diversity of biologically derived molecules that humans
have been exposed to throughout our evolutionary history. In light
of this, any health benefits we experience in the natural
environment should perhaps be regarded not as a boost to well-being
but as a return to our baseline state.

It seems that when we venture out to “take the air”, we get a great
deal more besides.

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