In the last year I’ve moved to Los Angeles, one of the smoggiest cities in America. On top of the heat and the smog that settles in around the foothills of LA, in August and September, there’s fire season. As I type this up, I’m looking out my window onto ominous skies and a light dusting of ash raining down thanks to the Bobcat fire making its way through the San Gabriel mountains less than 20 miles from my home.
If you’re like me, there’s no better mood booster than taking your daily workout outdoors. You may also sometimes wonder if you should head out for a run when your weather app is blaring an “unhealthy air quality for sensitive groups” warning and/or ash is raining from the sky from some local fire. So, let’s take a look at some of the research and recommendations around air quality and exercise.
Air Pollution Risk
If there’s one thing I learned from my environmental health class in graduate school, it’s that air pollution poses a major risk to health. On the other hand, exercise is known to have many health benefits including lowering risk of high blood pressure, stroke, insulin resistance, certain cancers, depression, even Alzheimers… the list goes on.
Unfortunately, athletes are at a higher risk of inhaling pollutants when exercising outdoors simply because of an increase in breathing (respiration rate) during exercise, increased airflow velocity carrying pollutants deeper into the respiratory tract, and breathing through the mouth which bypasses some of the nasal mechanisms for filtration of particles in the air.(1) That being said, different types of pollution may pose different risks and have various effects on training.
Common Types of Air Pollutants:
Carbon Monoxide (CO)
A number of studies have noted that CO exposure has been associated with elevations in heart rate, and less than optimal exercise performance in both healthy individuals and individuals with pre-existing conditions.(3)
Similarly, ozone may have an adverse effect on exercise performance, although there is still insufficient research on exposure and impact on training. Additionally an inflammatory response in the airways has been linked to ozone exposure, suggesting that pollution may promote oxidative stress in the airways, and this response may be increased with exercise. It is unclear, however, to what extent exposure may amplify the systemic inflammatory reaction one already has in response to acute bouts of exercise. (3)
Particulate matter also appears to have a negative impact on aerobic exercise capacity. Exercise itself is know to increase oxidative stress and inflammation, and particulate matter exposure during exercise may promote or exacerbate oxidative stress and inflammation. Additionally exposure to particulate matter during exercise may impact vascular function; however, more research is clearly needed.(3)
What About Wildfire Smoke?
Wildfire smoke is a tad different than your typical smog, but it’s actually one of the largest sources of unhealthy air quality. It’s often composed of carbon dioxide, water vapor, carbon monoxide, particulate matter, hydrocarbons, nitrogen oxides, trace minerals, and various organic chemicals.(8) Similarly, the major concerns when it comes to smoke are primarily carbon monoxide and particulate matter, which as we know aren’t great for your health, and may potentially cause respiratory symptoms, reduction in lung function, and pulmonary inflammation. Breathing in smoke can also have immediate health effects including: coughing, headaches, runny nose, trouble breathing, chest pain, shortness of breath, and fatigue, so you may want to be extra careful around smoke.
Air Pollution and Diabetes
Crazy enough, exposure to air pollution has also been associated with increased risk of diabetes (type 2, type 1, and GDM) in a number of studies, and some studies suggest that people with diabetes may be more susceptible to air pollution. That being said, to my knowledge, there have been no studies looking specifically at exposure during physical activity in people with diabetes.
Weighing the Pros and Cons
In general, the long-term benefits of regular physical activity outdoors are thought to outweigh the risks of potential harmful effects related to increased exposure to air pollutants that comes with regular exercise outdoors. That being said, exposure to higher levels of pollutants may actually negate some of the positive benefits associated with physical activity. Additionally, exercise outdoors in smoky conditions should be avoided if possible.
Here are a few tips when considering your Workout:
1. Monitor Air Quality and Consider the Following Guidelines:
Consider checking out AirNow, a website (& app) by the EPA which publishes air quality (AQI) levels as well as tracks smoke on their interactive map.
AQI 101-150 is considered unhealthy for sensitive groups, which includes pregnant women, children, seniors, and people with respiratory conditions (including asthma) or heart conditions. You may want to consider limiting your exposure, especially if you fall within one of the above groups. It might be helpful to take your workout indoors, keep windows closed and keep air conditioning on if you have it.
AQI 151-200 is considered unhealthy, and everyone is advised to reduce prolonged or strenuous activity and to take more breaks when exercising outdoors. The sensitive groups (listed above) are advised to avoid prolonged or heavy exertion and to move activities indoors.
AQI 201-300 is considered very unhealthy and everyone is advised to consider moving activities indoors. Sensitive groups are further advised to avoid all physical activity outdoors
AQI >300 is considered hazardous and it is recommended that everyone avoid all physical activity outdoors.
2. Switch up your route:
Even when the air quality is relatively good, you may want to avoid busy roads and high traffic areas, especially at rush hour, when emissions are higher. Reducing your exposure to pollutants in the long run may be beneficial.
3. Consider timing your outdoor activities for low pollution times:
Ozone levels are usually higher in the afternoon, especially on hot and sunny days. The best time for outdoor physical activity is before noon or after 6:00 PM
4. Choose cooler days:
Pollution levels tend to be higher on hot sunny summer (or California Fall) days, and lower on cool, rainy, or windy days.
5. Avoid strenuous work or exercise if in a smoky area
Curious whether there’s smoke in your area? Check out the AirNow interactive fire and smoke map!
- Carlisle AJ, Sharp NCC. Exercise and outdoor ambient air pollution. British Journal of Sports Medicine 2001;35:214-222.
- Exercise and air quality: 10 top tips. Breathe (Sheff). 2015;11(3):239-242. doi:10.1183/20734735.ELF113
- Giorgini P, Rubenfire M, Bard RL, Jackson EA, Ferri C, Brook RD. Air Pollution and Exercise: A REVIEW OF THE CARDIOVASCULAR IMPLICATIONS FOR HEALTH CARE PROFESSIONALS. J Cardiopulm Rehabil Prev. 2016;36(2):84-95. doi:10.1097/HCR.0000000000000139
- Roberts JD, Voss JD, Knight B. The association of ambient air pollution and physical inactivity in the United States. PLoS One. 2014;9(3):e90143. Published 2014 Mar 5. doi:10.1371/journal.pone.0090143
- Jiayun Yao,Michael Brauer,Julie Wei,Kimberlyn M. McGrail,Fay H. Johnston,and Sarah B. Henderson 2020. Sub-Daily Exposure to Fine Particulate Matter and Ambulance Dispatches during Wildfire Seasons: A Case-Crossover Study in British Columbia, Canada. Environmental Health Perspectives 128:6 CID: 067006 https://doi.org/10.1289/EHP5792
- Anderson JO, Thundiyil JG, Stolbach A. Clearing the air: a review of the effects of particulate matter air pollution on human health. J Med Toxicol. 2012;8(2):166-175. doi:10.1007/s13181-011-0203-1
- Sinharay, Rudy et al, ‘Respiratory and Cardiovascular Responses to Walking down a Traffic-Polluted Road Compared with Walking in a Traffic-Free Area in Participants Aged 60 Years and Older with Chronic Lung or Heart Disease and Age-Matched Healthy Controls: a Randomised, Crossover Study’ (2018) 391(10118) The Lancet (British edition) 339
- Larsen, A. E., Reich, B. J., Ruminski, M., & Rappold, A. G. (2018). Impacts of fire smoke plumes on regional air quality, 2006–2013. Journal of Exposure Science & Environmental Epidemiology, 28(4), 319–327. https://doi.org/10.1038/s41370‐017‐0013‐x
- Haikerwal, A., Akram, M., Del Monaco, A., Smith, K., Sim, M. R., Meyer, M., Tonkin, A. M., Abramson, M. J., & Dennekamp, M. (2015). Impact of fine particulate matter (PM2.5) exposure during wildfires on cardiovascular health outcomes. Journal of the American Heart Association, 4(7). https://doi.org/10.1161/jaha.114.001653
- Wildfire Smoke: A Guide for Public Health Officials, 2016
- Janghorbani, M., Momeni, F. & Mansourian, M. Systematic review and metaanalysis of air pollution exposure and risk of diabetes. Eur J Epidemiol 29, 231–242 (2014). https://doi.org/10.1007/s10654-014-9907-2