Newsletter #231

We have known for some time that physical activity improves your brainpower.

One mediator of this effect is brain derived neurotrophic factor (BDNF), a molecule that helps generate new brain cells and strengthen existing ones, and plays a key role in learning and memory. Circulating BDNF levels increase following physical exercise, especially high intensity interval training.

Air pollution, on the other hand, appears to have negative impacts on the brain, which is probably not super surprising. For example, one study of a large French cohort found that even relatively low levels of outdoor air pollution were associated with significantly poorer cognitive performance.

Recently, researchers have become interested in how air pollution interacts with exercise, for a couple of reasons. For one thing, a lot of people engage in physical activity outside, including active commuting. Additionally, ventilation rate increases during exercise - especially intense activity - which can magnify the effects of pollutants since you’re taking in more air. In the process of exploring this relationship, evidence has emerged suggesting that air pollution might effectively cancel out some of the beneficial physiological effects of exercise on the brain, and even increase risk of degenerative disease over time.

Researchers looked at data from 8,600 middle-aged participants in the UK. For one week, these subjects wore accelerometers to capture physical activity intensity and duration. They also underwent MRI imaging to examine the volume and health of their brain tissue. All of this data was then analyzed with estimated levels of air pollution at the residences of these participants. They found that vigorous physical activity was associated with greater gray matter volume, as well as reduced white matter lesions. However, for participants who lived in more highly polluted areas, the beneficial impact of vigorous exercise on white matter lesions was abolished. That research team then looked at the same type of data from 35,562 adults, and also examined inpatient hospital records for these subjects. They found, similarly, that vigorous exercise was generally associated with reduced risk of dementia, but exposure to air pollution attenuated this relationship, so much so that those in the highest tertile of exposure did not appear to benefit from vigorous exercise with respect to dementia risk.

Researchers in Belgium recruited 38 physically fit volunteers, and had them perform two cycling trials, each performed 2-4 weeks apart from one another. One trial was performed near the busiest road section in Belgium (the Antwerp Ring). The other was performed in a “clean” room that was treated with air filters. The duration and intensity of cycling was controlled and kept the same for each volunteer for both cycling trials. As expected, serum BDNF levels went up after cycling in the air-filtered room (+14.4%), a magnitude of increase that is pretty typical after a short, moderate-intensity bout of exercise. In contrast, BDNF concentrations did not rise after cycling near the major traffic route. The researchers attributed this disparity to inflammation associated with the air pollution.

Researchers in China recruited 101 older adults from Shijiazhuang in the Hebei province. Participants’ exposure to air pollution was estimated based on levels of various pollutants at their residential address, and blood samples were analyzed via PCR to determine levels of DNA methylation at the promoter regions of the BDNF gene. Here’s why: methylation is an epigenetic mechanism that controls whether and how much a given gene is expressed. When methylation occurs at the promoter region of a gene, it can prevent transcription factors (which would activate the gene) from binding, thus basically locking the gene into an “off” setting. Sure enough, the researchers found that long-term exposure to particulate matter was associated with greater methylation. They didn’t measure BDNF levels in serum, but prior research has shown that higher methylation of the BDNF promoter leads to suppressed BDNF expression and in turn to lower BDNF levels. This is likely why methylation of the BDNF gene has been found in various psychiatric disorders like depression, and BDNF promoter methylation has even been proposed as a potential preclinical biomarker for Alzheimer’s disease.

There isn’t a whole lot that you can do individually about outdoor air pollution other than stay inside when levels of pollutants are high (or move somewhere with cleaner air I guess?).

But the indoor environment has its own perils. Indeed, the EPA has estimated that concentrations of certain recognized air pollutants can be 2-5 times higher in indoor environments than outdoors, due to compromised dilution capacity in enclosed spaces. And fortunately, indoor air is much more actionable.

In this How-to Guide, we identify the main types of indoor air pollutants and go over what you can do to mitigate or eliminate them, as well as some fact-checking on a very popular (but scientifically dubious) method for purifying indoor air.

This is obviously a relevant concern for those of us who work in offices most of the day, but it's also key if you're a member of the WFH brigade. One recent study that installed air monitors in the homes of people working remotely during the pandemic found that fine particulate matter levels in the homes of every single participant exceeded air quality standards established by the EPA for a healthy work environment.

That's why we created this guide. It will show you how to test indoor air quality, and support maintenance of better air quality in your indoor spaces, for a healthier body and sharper mind.

Thanks for reading, enjoy the weekend, and we will see y'all next week!

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