Air pollution negates some of the beneficial effects of vigorous-intensity exercise.

Components present in air pollution – a mixture of toxic chemicals, gases, and particulate matter – can cross biological barriers, including the blood-brain barrier. Exposure to air pollutants is associated with poor health outcomes and an increased risk for both acute and chronic diseases. A recent study suggests that air pollution negates some, but not all, of the beneficial effects of vigorous-intensity aerobic exercise.

Robust evidence demonstrates that vigorous-intensity aerobic exercise (defined as activity that achieves a heart rate that is 70 to 80 percent of one’s maximum) benefits brain health. For example, vigorous-intensity aerobic exercise appears to activate the endocannabinoid system to promote motor sequence memory and learning. Other evidence suggests it improves mood.

The study involved 8,600 adult participants enrolled in the UK Biobank study. Participants wore wrist accelerometers to track their physical activity. They also underwent magnetic resonance imaging (MRI) to assess their structural brain volumes and identify the presence of white matter hyperintensities – areas of the brain that show up as distinct white areas on MRIs and indicate cerebral small blood vessel disease. The investigators estimated the participants' exposure to air pollution based on where the participants lived.

The investigators found that the more physically active participants were, the less their brains showed evidence of shrinkage, and the fewer white matter hyperintensities they exhibited – an effect roughly equivalent to being three years younger. Participants who were exposed to more air pollution exhibited greater brain shrinkage than those with less exposure – about the amount observed in one year of normal aging. However, participants who exercised the most and had the most exposure to air pollution demonstrated no evidence of more brain shrinkage, but they exhibited more white matter hyperintensities, especially if they engaged in vigorous-intensity aerobic exercise.

These findings support earlier studies that demonstrate the beneficial health effects of vigorous-intensity exercise on the brain but suggest that exercising in areas where air pollution is high negates some of these benefits. The authors recommended that because most air pollution comes from vehicle exhaust, people should exercise in areas far from heavily trafficked roads.

• View study abstract.

• Read about the many beneficial health effects of aerobic exercise in our overview article.