New Scientist
What if the air we breathe provides more than just oxygen? Tiny amounts of nutrients like iodine and manganese enter our bodies through the lungs and nose, potentially supporting health. These “aeronutrients” might explain benefits of nature and offer new ways to supplement nutrition, especially in confined spaces.
The wild idea that we all get nutrients from the air that we breathe
Author: Graham Lawton
AROUND 10 years ago, British tabloid newspaper The Sun ran a memorable article about a couple who claimed to be “breatharians”, able to survive on a little water and even less food. Instead, they said, they derived sustenance from air, sunlight and the energy of the universe. The story was picked up by media outlets across the world and propelled the couple and their unusual lifestyle to fame – and no small amount of ridicule.
Needless to say, humans – even self-described breatharians – can’t live primarily on air and sunlight, as some practitioners tragically discovered when they died trying. But weirdly, the concept turns out to be more substantial than it first seems. According to a duo of Australian scientists, we can and do derive nutrients from the air – nowhere near enough to live on, but perhaps enough to benefit our health. Is it possible that a source of nutrition has been under our noses all along?
“The evidence shows very clearly that we can absorb nutrients from the air we breathe,” says Flávia Fayet-Moore, a nutrition scientist at the University of Newcastle in Australia. Whether or not these “aeronutrients”, as the pair have dubbed them, make a significant contribution to our health isn’t yet clear, she says – but they could in the future.
Every day, we breathe around 7000 to 8000 litres of air, a mixture of nitrogen, oxygen, argon, water vapour and whiffs of other gases. Our lungs extract oxygen and replace it with waste carbon dioxide. But air can also contain trace amounts of compounds not normally thought of as airborne, many of which have nutritional value when we ingest them. Fayet-Moore and her colleague Stephen Robinson at RMIT University in Bundoora, Australia, are investigating what happens when we inhale them.
Their starting point was a 2019 article by Paul Trayhurn, a nutritional biologist at the University of Liverpool, UK, who argued that oxygen should be reclassified as a nutrient. Trayhurn pointed out that despite being absorbed through the airways rather than the gastrointestinal tract, oxygen meets the definition of a nutrient as “a substance that provides nourishment for the maintenance of life and for growth”.
The idea didn’t catch on, but it did catch the eye of Robinson. Over dinner one evening, he and Fayet-Moore got talking about the oxygen-as-nutrient concept and wondered whether air might contain other beneficial compounds that we absorb into our bodies. Curious, they trawled through the literature and uncovered ample evidence that it does, and we do.
“We were trying to disprove it, but the more we read into it, the more the evidence started piecing together and we were like, ‘How is this possible? How has no one ever noticed this until now?’ ” says Fayet-Moore.
To determine whether aeronutrients really were possible, the pair first needed to figure out the mechanisms by which inhaled compounds can be absorbed by the body. Inhaled air’s first port of call is the nasal cavity, where the nasal microvasculature, a dense bed of tiny blood vessels separated from the airway by a thin layer of cells, heats and humidifies it. Airborne molecules readily diffuse into this layer of cells, which is primarily how snortable drugs of misuse, such as cocaine, enter the bloodstream. Intranasal drug delivery – which, owing to the area’s permeability, is rapid – is also increasingly being explored for other uses, including analgesics, sedatives and migraine treatments.
The nasal cavity also provides direct access to the central nervous system via the olfactory epithelium, a patch of nerve endings linking the airspace to the brain’s smell centre, the olfactory bulb. This is the only part of the brain in direct contact with the environment and so offers an opportunity for the administration of drugs targeting the brain. Current research is exploring a “nose-to-brain” route for giving medication, such as intranasal insulin to treat dementia and post-traumatic stress disorder, and oxytocin to manage anxiety disorders.
The final destination for inhaled air is the lungs and these, too, are capable of transferring molecules from the air into the bloodstream. The terminal ends of the airways – tiny, densely capillaried sacs called alveoli – are principally involved in gas exchange, but can also facilitate the rapid absorption of other molecules, such as anaesthetics, nicotine, cannabinoids and opioids. In addition, therapeutic molecules, such as insulin, vitamin B12 and a form of vitamin A called all-trans retinoic acid, can enter the bloodstream via the lungs.
All of this suggests that, if there are nutrients in the air, they will be taken into the bloodstream, the brain, or both, says Fayet-Moore (see “How aeronutrients could work”, below). But are there nutrients in the air? Again, the existing literature says there are.
The most compelling evidence is for iodine, a trace element micronutrient required to synthesise thyroid hormones. We usually obtain it from food – seafood is an abundant source, as are dairy products and crops grown in naturally iodine-rich soil – however, access to those foods can vary. In 1960, around 60 per cent of the world’s population was iodine deficient, which can cause an enlarged or underactive thyroid. That situation has largely been rectified with iodised table salt, but significant pockets of deficiency remain.
In 1964, iodine expert Robert Vought at what was then the US National Institute of Arthritis and Metabolic Disease had a thought: maybe air was an important source of iodine? He and his colleagues found that the concentration of gaseous iodine in outdoor air ranged from zero to 7.4 micrograms per cubic metre and estimated that inhaling iodine-rich air could supply around 7.3 per cent of the US recommended adult intake of 150 micrograms per day. They also studied a group of laundry employees who were exposed to elevated atmospheric iodine at work, finding that their blood and urine contained higher amounts of the element compared with a matched group who worked outside. Vought speculated that they were absorbing iodine through their airways, but couldn’t rule out other routes.
We can absorb nutrients from the air we breathe
A few years later, in 1968, a team led by D. J. Morgan at the UK Atomic Energy Authority asked volunteers to inhale radioactive iodine gas – an isotope with a short half-life that is typically used in thyroid function tests and tracer studies – to determine the radiological hazard of an accidental release of the gas. The research found that iodine could indeed be absorbed by the airways and could be carried by saliva into the small intestine.
But research into inhaled iodine lay fallow until 2011, when a team led by Peter Smyth at the National University of Ireland in Galway took a look at airborne iodine absorption in the wild. The researchers compared three groups of people: some living near beaches where there was a lot of seaweed, a rich source of iodine gas; some living near beaches with little seaweed; and others living inland. The first group had the highest levels of iodine in their bodies and the lowest incidence of iodine deficiency, which Smyth surmised was because they were inhaling the stuff into their bloodstreams. “The eureka moment for me was these iodine studies,” says Fayet-Moore.
The evidence for other aeronutrients may be weaker, but it isn’t non-existent. We know, for example, that the micronutrient manganese, a component of the detoxifying enzyme glutamine synthetase in the central nervous system, can enter the brain via the olfactory epithelium. Manganese – in the right amounts – is a trace metal element essential for certain metabolic brain functions. Present in soil, it can be dispersed into the air as tiny particles through soil erosion or human industrial processes, such as fossil fuel combustion. Concentration depends on location – higher near industrial areas, lowest in rural areas. However, says Fayet-Moore, it is plausible that we acquire much of what we need by breathing it in .
At first glance, that appears unlikely: breathing in 7000 litres of air a day could deliver about 100 nanograms of manganese, which is a fraction of the US recommended dietary intakes of 2.3 milligrams for men and 1.8 milligrams for women. But manganese acquired through diet is largely excluded by the blood-brain barrier, the semi-permeable membrane that protects the central nervous system from potentially harmful substances in the blood, says Fayet-Moore. As a result, we have to eat considerably more than we require to see a benefit.
Nose-to-brain
The nose-to-brain route, on the other hand, delivers it directly to where it is needed, so its effect could be potent. “Not only can we absorb nutrients from the air, but we can absorb them more efficiently than we can from our guts,” she says. “The amounts of nutrients in air are minute, yes, but our respiratory airways are way more efficient at absorbing molecules than our gut.” In fact, it can be too efficient: welders exposed to high levels of airborne manganese are at risk of accumulating neurotoxic amounts via the nose-to-brain route, sometimes resulting in cognitive impairment and Parkinson’s-like symptoms.
Two other micronutrients, zinc and iron, may also enter the brain via the olfactory epithelium, says Fayet-Moore, but the evidence for these being present in air in significant amounts is lacking.
Another promising candidate is all-trans retinoic acid, which is typically acquired by eating carrots, sweet potatoes and other foods containing beta-carotene. It is essential to embryonic development, as well as cellular regeneration and immune function. All-trans retinoic acid has been shown to occur naturally at the air-water interface of rivers, lakes and oceans, suggesting that it could be in the air in significant amounts.
There could be other, yet-to-be-discovered nutrients in the air that we only acquire by breathing, says Fayet-Moore. But even if aeronutrients currently contribute little or nothing to our natural intake of micronutrients, there is an opportunity to exploit the fact that they could supply more. It is surprisingly common for people to lack micronutrients – a recent global analysis found significant deficits for 15 of them, including iodine, vitamin E and calcium – and supplementation by inhalation might be an effective way to address this, says Fayet-Moore. “One in two people globally are deficient in vitamin D. The prescription might be: ‘Sit here and inhale vitamin D for a few minutes and you’re sorted for the next month.’”
Fayet-Moore, who is also a space nutritionist, suggests that aeronutrients could be useful in artificial environments, where the air is filtered. “They are potentially going to play a big role in closed loop ecosystems like submarines and space stations.”
Aeronutrients may partially explain the mysterious health benefits of spending time in nature, too. “All the evidence that exists on nature therapy, like ‘forest bathing’, shows quite conclusively the health impact: if you spend more time in nature, you’re healthier,” says Fayet-Moore. “But no one really knows why. There are lots of hypotheses. We think that one of the reasons might be aeronutrients.”
When she and Robinson published their idea, also suggesting that inhaled bacteria, “aeromicrobes”, could similarly contribute to human health, in the journal Advances in Nutrition, they expected pushback from nutrition scientists. But the reception has been surprisingly positive, she says. “Typically, academics approach the concept of aeronutrients cautiously – until they read the evidence,” she says.
According to Jean Debédat at the University of California, Davis, the article has been shared among several nutrition working groups and many experts found it intriguing. He came across the idea when the journal invited him to write an accompanying editorial. “I have to admit I was initially really sceptical,” he says. “However, after digging deeper, I found the idea fascinating. It does make sense: we are breathing thousands, maybe millions, of small molecules with every breath. Like all molecules, some get absorbed, and likely have different bioactivities, some good, some bad. It’s clear to me that there is a lot of potential here.”
One in two people are deficient in vitamin D. The prescription might be: ‘Sit here and inhale it’
Trayhurn – the oxygen-as-nutrient scientist – is also impressed. “The concept that they develop is compelling, and the arguments and the evidence that they marshal are strong,” he says. “The data on manganese and iodine is particularly intriguing. There is, of course, a question of how large a contribution aeronutrients make – or could make – to intake, but the iodine studies suggest that, for some nutrients, it is considerable.”
Having tested the waters, Fayet-Moore and Robinson now want to test the air. “We need more research to understand the amount of nutrients that are naturally occurring in nature,” she says. They also want to test whether delivering micronutrients in inhalable form would work, although the existing literature on vitamin B12 and other therapeutic treatments suggests that it will.
After that, who knows? “We’re only at the very beginning of this field,” says Debédat. “It reminds me a bit of how the microbiome field looked 25 years ago: people knew it was there and probably important, but most researchers really didn’t pay too much attention to it. It wasn’t until new methodologies emerged that the field really exploded. I believe that the field of aeronutrients might follow the same path in the coming years.”
For a fusty old area like nutrition science, that would be a breath of fresh air.
Credits: TCA, LLC.