I’m a resident of both New York City and Los Angeles, which means that I spend a lot of time in big cities breathing in air of dubious quality. And I’m not alone; more than 166 million people in the United States—52 percent of all Americans—are exposed to unhealthy levels of pollution, putting them at risk for premature death and other serious health effects.
The impact of air pollution on diseases like asthma, lung cancer, and heart disease is well-established. Less understood, however, is the impact that dirty air has on our brains. And yet, evidence is mounting that air pollution has a profound impact on our cognitive function as well as our long-term brain health.
An introduction to airborne particles.
Recent research has focused on particle pollution, one of the two main types of pollution in the United States (the other being ozone pollution). These particles are airborne, which gives them the ability to enter our lungs and circulate. The most dangerous types of airborne particles are those measuring 2.5 micrometers or smaller (PM2.5 for short). These particles are invisible to the naked eye (about 3 percent of the diameter of a human hair) and come from power plants, industrial processes, vehicle tailpipes, wood stoves, and wildfires.
Once inside of you, PM2.5 poses a strong risk to our vascular systems, contributing to dysfunction of the blood vessels. In a small trial, healthy people exposed to very high concentrations of PM2.5 had a steep decline in heart rate variability (an important measure of heart health) and an increase in heart rate. As you might imagine, vascular dysfunction is a contributing factor to heart disease, but it also plays a major role early on in the development of Alzheimer’s disease and other forms of dementia.
Pollution and the blood-brain barrier.
One vascular network that you certainly don’t want to mess with is the blood-brain barrier. This barrier keeps your damage-prone brain safe from chemicals in your blood that might harm it. Unfortunately, PM2.5 has been shown to cause blood-brain barrier dysfunction in young people and even promote the appearance of the two hallmarks of Alzheimer's disease. And disruption of this barrier isn’t just linked to Alzheimer’s disease; autism, multiple sclerosis, epilepsy, and Parkinson’s disease are all associated with blood-brain-barrier dysfunction.
One tiny PM2.5 particle is called magnetite. Magnetite is made of iron and is commonly found in the air of big cities. When we breathe it in through our noses, it's able to enter the body and travel up to the brain. Once there, it can "infect" multiple regions including the memory-processing hippocampus, which is among the first structures to be damaged in Alzheimer’s disease. Shockingly, these nanoparticles have been discovered in the brains of children as young as 3, causing inflammation and impaired cognitive function.
So can pollution actually cause dementia to develop? That’s an unknown at this time, but given all of the research above, it would seem plausible at the very least. One study, which sought to answer this very question, found that residing in an area with high levels of air pollution increased risk of cognitive decline by 81 percent and Alzheimer's disease by 92 percent. In fact, 20 percent of Alzheimer's cases may be due to exposure to high levels of fine particulate matter. (These are correlational figures, which would need to be validated by further research.)
Here's what you can do to protect yourself.
Alas, I don’t envision a mass exodus from the world’s greatest cities after people read this article. So if we do happen to live in a city with air pollution, what can we do to protect ourselves? Thankfully, modern science provides some clues as to how we might enhance our protection against these unsavory airborne antagonists. Here are eight of them:
1. Arm yourself with knowledge.
It’s easy to find out the level of PM2.5 in your city—just keep in mind that this figure varies day-to-day and even minute-to-minute. To find out if you're in a high-risk area, get your city's air quality index (AQI) here and then plug it in here to see your local PM2.5 exposure.
Levels over 35 micrograms of PM2.5 per cubic meter of air are considered high risk. On days when the Air Quality Index (which incorporates the PM2.5 concentration) exceeds 100, it’s probably best to keep outdoor activity light.
2. Eat your B vitamins, or consider a supplement.
In a small trial, healthy people who took a daily B complex containing 2.5 mg of folate, 50 mg of vitamin B6, and 1 mg of vitamin B12 seemed to be completely protected against pollution-induced vascular dysfunction and inflammation. How might this "B"? B vitamins assist in the body’s detoxification pathways, and it all comes down to methylation.
Methylation is a primary method of removing toxins in the phase 2 liver detoxification process. B vitamins (like methylfolate and methylcobalamin) provide methyl groups that convert toxins of all kinds from insoluble or fat-soluble compounds into water-soluble compounds. Only once these toxins are made water-soluble can they be easily eliminated from the body via urine, sweat, and bile. Unfortunately, deficiencies in vitamins B6, B12, and folate are common, due to intakes being suboptimal in perhaps 40 percent of the population. Consuming adequate B6, B12, and folate (from beef, chicken, eggs, and dark leafy greens) is critical. If you choose to go the supplement route, ensure that the brand you choose contains the activated form of folate as it increases bioavailability.
3. Consume omega-3-rich foods, or consider supplementing with fish oil.
Most people underconsume omega-3 fatty acids while overconsuming omega-6 fatty acids. Omega-3s are abundant in the fat of wild fish, pastured eggs, and grass-fed beef. In a small trial involving mice exposed to PM2.5, omega-3 fatty acids were found to both prevent and treat the inflammation and oxidative stress caused by air pollution, adding up to a 30 to 50 percent reduction in harm. Amazingly, this trial was reproduced in elderly people living in Mexico City with similar results.
4. Eat more cruciferous vegetables (especially broccoli sprouts!).
Raw cruciferous vegetables (like kale and broccoli) are rich in compounds called glucosinolates, which react with enzymes when they're chewed to create a new compound called sulforaphane. Sulforaphane is a potent activator of phase 2 detoxification in the body and helps you to excrete these particles. In a study performed in heavily polluted parts of China, participants given beverages containing sulforaphane significantly increased their metabolism and excretion of hazardous air pollutants (in this case, neurotoxins called benzene and acrolein). Another study found that sulforaphane protected against the pro-oxidant effects of diesel emission by stimulating the production of endogenous (made-in-the-body) antioxidant enzymes.
The top dietary source of sulforaphane is young broccoli sprouts, containing 50 to 100 times the sulforaphane-producing compounds of adult broccoli. On my own website, I have detailed the easiest method of growing your own broccoli sprouts, which I highly recommend you check out. I always have a batch on hand and regularly add them to my salads or smoothies.
5. Load up on antioxidant-rich foods.
In a study of people exposed to coal-burning emissions from an electric power plant, levels of vitamins C and endogenous antioxidants were reduced, suggesting that exposure to pollution depletes our body’s limited antioxidant abilities. However, six months of supplementation with vitamin E and C (800 mg and 500 mg, respectively) was effective in decreasing markers of lipid and protein damage and improved antioxidant defenses. Foods high in vitamin C include kale, berries, broccoli, and citrus fruits. Foods high in vitamin E include almonds, avocado, and spinach.
6. Get some sun, or consider supplementing with vitamin D.
Vitamin D regulates the expression of nearly 1,000 genes in the human body, many involved in immune homeostasis. Thankfully, your skin makes vitamin D quite simply—via exposure to the sun’s rays. The bad news is that those rays have a long way to travel before they hit your skin. And if you live in an area of high pollution, air particles can interfere with those precious UVB rays. City dwellers may be particularly vulnerable to vitamin D deficiency for this reason. My advice? Get your vitamin D levels checked by your doctor to ensure adequate levels (between 50 ng/mL and 80 ng/mL is considered ideal by the Vitamin D Council). If they’re low, consider a vitamin D3 supplement.
7. Get out into nature!
Trees are more than just nice to look at; they dutifully filter the air of airborne pollutants like PM2.5. That’s why we need more of them around, and any chance we get to spend time in nature should be one we relish. The U.S. Forest Service found that in New York City alone, trees save an average of eight lives every year. Generally speaking, the greater the tree cover, the greater the pollution removal. So, if you live in a polluted area, use weekends to frolic in nature, giving your detox systems a chance to catch up.
8. Consider an air filter mask for urban exercise.
Filter masks are graded according to the percentage of particles greater in size than 0.3 micrometers that they can filter out. An "N95" mask (here’s one example) means that the mask is able to filter out 95 percent of particles 0.3 micrometers or larger (PM2.5 particles are 2.5 micrometers, so these masks would easily filter them out). An N100 mask (such as this one) would filter out nearly 100 percent of these particles. While I’m not recommending wearing one all the time, they may be useful for things like biking in large cities, when you find yourself spending time exercising next to traffic—common in a pedestrian city like NYC.
9. Call up the Environmental Protection Agency (EPA) and demand stricter laws.
The EPA’s current guidelines limit the amount of PM2.5 in the air to an annual average of 12 micrograms per cubic meter of air. But this may not be strict enough, according to a recent analysis published in the New England Journal of Medicine (NJEM). The study found that even at 10 micrograms per cubic meter of air, PM2.5 contributed to a more than 7 percent increased risk of early mortality. Another study by the American Thoracic Society and the Marron Institute of Urban Management at New York University found that just by lowering the EPA’s standards from 12 μg/m3 to 11 μg/m3, 9,320 deaths and 21,400 serious health events (such as heart attacks, hospital admissions and emergency room visits) could be prevented annually.
Interestingly, the association between pollution (below national guidelines) and early mortality in the NJEM study I mentioned was particularly strong for minorities and low-income groups—the same groups that are at highest risk for nutrient deficiencies. My informed guess is that the harmful effect of pollution is fed by inadequate nutrition, which might hurt our ability to "detox" from some of these airborne pollutants. So, eat healthy today to make sure that you’re stacking the odds in your favor for a better tomorrow!