We all know hitting the gym (or at least a brisk walk) lowers your risk of dying early and keeps diseases like diabetes and heart disease at bay. But here’s the catch researchers have been scratching their heads over: what if you’re exercising while breathing dirty city air? Are you helping your body… or slowly wrecking it?

A new mega-study out of the UK tried to settle this once and for all.

The Setup

  • Who they studied: Hundreds of thousands of Brits from the UK Biobank.
  • What they tracked: Physical activity (both self-reported and measured with accelerometers) + exposure to multiple air pollutants.
  • What they wanted to know: Does air pollution cancel out the benefits of exercise on things like heart disease, diabetes, COPD (lung disease), cancer, and overall mortality?

The Findings (a.k.a. the good news)

  • Exercise wins. Across the board, people who moved more had lower risks of dying and developing chronic diseases.
  • Air pollution is still bad. Fine particulate matter (PM2.5) was strongly linked to COPD and other problems, but its damage wasn’t big enough to outweigh the benefits of staying active.
  • Type 2 diabetes stood out. Exercise showed the strongest protective effect here.
  • Data matters. Accelerometer-based activity tracking was way more accurate than people self-reporting how often they hit the treadmill (no surprise — we all exaggerate).

The Nuance

  • In South Korea (where air pollution is way higher), studies suggested that exercise in smoggy areas could increase cardiovascular risk. But the UK’s pollution levels aren’t as severe, so the “pollution cancels exercise” theory didn’t hold up.
  • Kids might be more vulnerable — some research hints at air pollution messing with asthma and fitness in children.

The Big Takeaway

Even if you live in a smoggy city, moving your body is still one of the best things you can do for your health. Exercise doesn’t erase the harm of air pollution (we still need cleaner air), but it doesn’t become “bad for you” just because the air isn’t pristine.

Or put simply: it’s still better to jog in London than to sit on the couch in clean mountain air.

Huang M, Olsen JR, Trost SG, Celis-Morales C, Pell JP, Ho FK. Physical activity, air pollution, and incident long-term conditions: a prospective cohort study. BMC Med. 2025 Aug 22;23(1):491. doi: 10.1186/s12916-025-04338-x. PMID: 40847357.