Air Pollution and Sleep Health - The Apeiron Life Perspective

What is it:

Air pollution is a major public health concern. According to the World Health Organization (WHO), nearly all people (99%) live in areas where ambient air pollution exceeds recommended guidelines. Over two billion people worldwide are exposed to harmful indoor air pollutants from using open fires or inefficient stoves. The WHO estimates that combined indoor and outdoor air pollution results in nearly seven million premature deaths yearly.

While low- and middle-income countries tend to experience the worst air pollution, the United States is far from exempt. Check where your city ranks on the American Lung Association’s resource listed in the references section at the end of this article.

Air pollution is an umbrella term for various compounds produced by vehicle emissions, manufacturing, construction, residential wood burning, road dust, paints, lacquers, plastics, pollen, molds, and anything else that produces small, airborne particles. The main offenders include fine particulate matter, oxides of nitrogen, sulfur dioxide, ground-level ozone, secondhand smoke, and carbon monoxide.

A growing body of evidence demonstrates associations between these pollutants and poor sleep quality. This article will give a broad overview of how air pollution negatively impacts health, summarize what we know about the specific effects on sleep, and suggest some actionable solutions to minimize exposure.

The purported claims:

Air pollution is associated with accelerated aging, cardiovascular disease, and worse mental health.
Airborne irritants can exacerbate sleep-disordered breathing and reduce the effectiveness of sleep apnea treatment.
Exposure during pregnancy can trigger epigenetic changes postpartum.

What the science says:

Every day, we come into contact with invisible airborne pollutants that interact with our skin, enter our airways, and can have a whole host of downstream effects on our physiology.

Skin is an essential protective barrier, but microscopic particles can cause allergic reactions and flare-ups such as atopic dermatitis. With chronic exposure to air pollution, DNA damage and inflammation can become sustained, which promotes cell dysfunction and aging.

Of greater concern is when these particles enter the body. Depending on the particle size, inhaled pollutants are deposited in the nose, upper airways, or even as far into the lungs as the alveoli themselves. The very smallest compounds can enter circulation, permeate a variety of tissues, disrupt the integrity of blood vessels, and even enter the brain.

Once in the brain — but also elsewhere in the body — these particles cause oxidative stress. This occurs when unstable molecules are left to run riot in the absence of neutralizing antioxidants, triggering cell damage and a subsequent immune response. Damage to blood vessels prompts pro-inflammatory cells to migrate to the damaged area, increasing the risk of plaque formation. Of great concern is when this occurs in the tiny blood vessels in the brain. It is thought to be one of the mechanisms by which air pollution is associated with Alzheimer’s disease and other dementias.

Both animal and human studies have shown that the worse the air pollution, the worse the cardiovascular health outcomes. Increased cardiovascular-related hospitalizations and deaths have been reported in areas where particulate matter (PM) is high. One hypothesis is that the lungs sense the fine PM and trigger an autonomic nervous system imbalance in favor of sympathetic output (i.e., “fight or flight” mode). It can trigger arrhythmias and increase blood pressure, putting individuals at greater risk of cardiovascular events.

PM is also associated with metabolic dysfunction. In a study of long-term PM2.5 exposure in Ontario, Canada, researchers noticed that participants had altered cell signaling in their adipose tissue, reduced insulin sensitivity, fatty liver, and endoplasmic reticulum stress. The endoplasmic reticulum is the important cell site for protein synthesis. When stressed, its ability to produce essential proteins becomes impaired. This prevents the cell from properly replenishing resources.

Aging

Hypertension is known to impair the brain's glymphatic system. This is a vital process that occurs during deep sleep, in which a convection current of cerebrospinal fluid becomes activated in the brain to flush out metabolic waste. This waste is directly associated with elevated odds of developing mild cognitive impairments and dementia, and may be one of the mechanisms by which air pollution indirectly promotes aging. The glymphatic system is sensitive to changes in neuroinflammation, autonomic arousal, and sleep disruption — all of which can be caused by air pollution.

Sleep is essential for promoting a longer healthspan and lifespan. It restores cell function and gives us the energy that we need to make the most of waking life. But it has been shown that sleep can be modulated by air pollution.

In a study of middle-aged and older adults in the UK, it was shown that PM with a size of less than 10 µm, along with nitric dioxide (NO2) were associated with poorer quality sleep and the highest rates of accelerated aging. PM2.5 can decrease the length of telomeres — the protective caps found at the end of our chromosomes which preserve our genome. PM can also lower mitochondrial DNA content and reduce expression of sirtuin-1, a gene coding for increased mitochondrial biogenesis and expression. Given that mitochondria produce energy for our cells, air pollution accelerates aging by reducing cell vitality. Sirtuin-1 expression has been shown experimentally to reduce aging in mice.

In a study of Chinese college students, the worse the air pollution exposure, the shorter the sleep duration. This may have been due to some direct pathway by which airborne pollutants disrupted sleep onset or consolidation, or indirectly as a result of worse health resulting from inflammation brought about by the polluting compounds.

Among other things, sleep supports the immune system. This becomes critical when the body is faced with excess inflammation due to air pollution insults. A vital part of the inflammation management system is a nightly dose of melatonin, a potent antioxidant, and hormone that becomes available to us at the onset of darkness. One can imagine a scenario where light pollution combines with air pollution to further curtail sleep, simultaneously depriving individuals of melatonin's significant antioxidant properties. Ambient air pollution is often worse in the most urbanized areas of the country, which also typically have the greatest noise and light pollution, which can converge to disturb sleep.

One of the mechanisms by which air pollution may directly impact sleep is through its ability to trigger vasoconstriction (the narrowing of blood vessels). A drop in core body temperature is needed for sleep to occur. This is one of the reasons that a warm bath or shower before bed makes many people fall asleep more quickly — peripheral blood vessels dilate to allow the body to cool itself. In a scenario where vasodilation is inhibited (perhaps due to airborne pollutants), there may be disruption in the sleep-onset process.

A recent study looked at how various air pollutants altered sleep architecture (that is, the time spent in different sleep stages across the night) in more than 4,800 people. A sub-sample of 50 people also completed additional cognitive tests and had their brains imaged. The researchers found that sleep architecture changed in different ways in response to different pollutants. Cognitive function also worsened across the board, reflected by brain changes in areas associated with executive function and learning. There's much still to learn about how different sleep stages relate to different aspects of health, but the changes seen in this study could be indicative of general disruption to the sleep-wake system.

Sleep Disordered Breathing

A review published in 2020 aggregated all of the studies on air pollution and sleep that were conducted between 2010-2019. The researchers couldn’t perform a meta-analysis of all the data due to significant differences in how they were collected. Still, they showed that nearly every study found sleep to worsen in the most polluted areas. The main reported sleep-related problems included irritated airways and exacerbated sleep-disordered breathing.

A meta-analysis published the following year found that PM and NO2 were significantly associated with poor sleep quality, presumably due to breathing-related conditions. Several studies have shown that air pollution can create sleep apnea where it wouldn’t otherwise exist. Poor air quality can also worsen mild cases, triggering a moderate or even severe suite of symptoms. Particles do this through a variety of mechanisms. First, they can damage the mucociliary lining of airways. They can also narrow the airways as a result of inflammation. Fine PM can also translocate through the olfactory nerve directly to the brain, where neuroinflammation may alter the brain areas that regulate ventilation during sleep.

Higher ground ozone (O3), sulfur dioxide (SO2), and humidity were associated with increased wheezing-related sleep disturbances in a study of young children. In another study, O3, PM, NO2, and carbon monoxide (CO) all decreased the effectiveness of the leading obstructive sleep apnea treatment — continuous positive airway pressure (CPAP).

Some evidence suggests that air pollution might decrease serotonin levels. Serotonin is essential for mood and plays a direct role in switching off rapid eye movement sleep in the brain, as well as promoting wakefulness. In a recent study of air pollution and psychological stress during pregnancy, it was shown that worse PM — particularly during second trimester — worsened the effects of psychological stress. This impaired the movement of serotonin between neurons. Interestingly, this was associated with changes in the newborn infant’s temperament.

Many researchers have linked air pollution with worse mental health, such as anxiety or depressive symptoms. It is theorized that neuroinflammation and sleep disturbance may play a causal role.

Our take:

The relationship between air pollution and sleep is complex, as health is an intricate web of feedback loops. There may be some direct pathways by which airborne particles disrupt the sleep-wake system, but similar to what happens in the event of a poor-quality diet or limited physical activity, a confluence of things can go wrong in the body in response to pollution, creating an unhealthy biological state that makes sleep more challenging. Air pollution worsens sleep via inflammation in the airways, but it is also linked to cardiometabolic disorders, obstructive sleep apnea, and mood problems.

Pollution sources extend beyond airborne particles alone. We are exposed to microplastics in our water and a variety of endocrine-disrupting compounds in personal care products, non-organic foods, and most food packaging. While avoiding these chemicals entirely is virtually impossible, there are a few easy, practical solutions to mitigate risk.

Consider using an air purifier in your home and workplace. A Wirecutter article with a variety of options is listed in the references below. Secondly, consider adding naturally air-purifying plants to your home. Many plants, including English ivy, peace lilies, snake plants, and Dracaena species have been NASA-tested for their ability to filter out benzene (found in gasoline, plastics, paints, and detergents) and formaldehyde (found in manufactured wood off-gases, carpet backing, and dry-cleaned clothes). An Architectural Digest article on how to strategically add plants to your bedroom is listed in the references below.

Beyond these simple home solutions, support green spaces in your community. Plants are not only potent chemical-filtration systems but also benefit mental health. A green space is preferable for exercise, any day of the week, but particularly on poor air quality days, so be sure to consider this in your routine.

Will this benefit me?

Airborne pollutants are one of the more insidious categories of pollution because they are so tricky to detect. Be sure to take a closer look at air quality inside and surrounding your home and workplace if you struggle with any inflammatory conditions — particularly if they are breathing-related. Targeting and ameliorating inflammation improves tissue function and quality of life.

Still curious to try it? If you do, here’s what to keep an eye on:

Prevent irritating airborne compounds from entering your home in the first place by opting for natural cleaning and personal care products. If you have any construction work done at home or in the office, or interior updates such as newly installed flooring or upholstery, be sure to ventilate the space well in the days that follow. Lastly, when it comes to central heating and cooling, change filters regularly, and have furnaces inspected by trained professionals.

References & additional materials:

Air pollution near you - https://www.lung.org/research/sota/city-rankings/most-polluted-cities

EPA air quality trends - https://www.epa.gov/air-trends/air-quality-national-summary

Air pollution and skin aging - https://pubmed.ncbi.nlm.nih.gov/35883663/

Air pollution and cardiovascular disease - https://pubmed.ncbi.nlm.nih.gov/25882781/

Glymphatic system and air pollution - https://pubmed.ncbi.nlm.nih.gov/37777345/

Air pollution meta-analysis - https://pubmed.ncbi.nlm.nih.gov/32912798/

Air pollution systematic review - https://pubmed.ncbi.nlm.nih.gov/32443219/

Air pollution and sleep duration - https://pubmed.ncbi.nlm.nih.gov/31514480/

Air pollution and aging - https://pubmed.ncbi.nlm.nih.gov/26672058/

Aging and SIRT1 - https://pubmed.ncbi.nlm.nih.gov/32084459/

Air pollution and sleep architecture - https://pubmed.ncbi.nlm.nih.gov/35258725/