Is it Safe to Walk or Run Outdoors When Air Pollution is High?

Today, on the 8^th of December 2022, the Air Quality Index (AQI) in my neighborhood in Mumbai is 318. This poor air quality is considered severe air pollution. Most of the Western world has AQIs less than 20-50…a value of 318 puts Mumbai on par with Delhi, considered among the most polluted cities in the world.

The general recommendation is not to exercise outdoors when the AQI is above 100 or 150, because the harder we breathe, the more we inhale PM_2.5 and other noxious particles, leading to short and long term adverse consequences. Two recent articles have shown an increase in the incidence of heart attacks and deaths with both short-term and long-term exposure to air pollutants [1,2].

I went for a run two days ago when the AQI was above 300 and I just could not run as fast as usual. I have also developed a rasping cough over the last 2-3 days, which I believe is due to the marked increase in the poor air quality around me. I am wondering whether I should go for a run/walk this morning or exercise indoors.

To set the context. Air pollution is the single largest leading cause of death in our country and most parts of the world. As I wrote last year, there is hardly any part of the country that meets current guidelines of good quality air, whether we use the WHO guidelines (PM2.5 exposure should be less than a mean of 5 µg/m3 annually, with a 24-hour mean of less than 15 µg/m3) or the Indian guidelines (PM2.5 of 60 µg/m3 annually with a 24-hours mean of less than 40 µg/m3). On the other hand, physical activity (PA) is the single best preventive method to increase our healthspan and lifespan, as we have seen multiple times over the last two years.

There are three questions to be answered.

1. Is it safe to exercise and be physically active in environments with high levels of air pollution as compared to not being active?

There are many studies that have assessed the impact of PA in settings of moderately high air pollution and shown that any PA is better than none across all levels of air pollution [3]. In the long term, the beneficial effects of PA trump the harmful effects of air pollution at all levels of physical activity. So, irrespective of the extent of air pollution, it is still better to exercise than not.

2. Should you exercise at home or is it safe to walk or run outdoors even when the AQI is high, with the assumption that the indoors environment has a reduced AQI due to air-filters?

With moderate to vigorous PA, there is an increase in the respiratory rate and respiratory airflow with more mouth breathing, which can potentially increase the impact of particulate matter pollutants in the short and medium term.

If indoor barriers to air pollution do not exist (e.g. open windows, no air filters), then it doesn’t matter where you exercise.

There aren’t too many studies that have addressed this question, but the general understanding is that it doesn’t really matter whether you are indoors or outdoors, unless you are at risk for respiratory diseases (e.g. asthma, other illnesses). One study from Dhanbad [4] has suggested that there is increased inhalation of air pollutants when outdoors while exercising as compared to indoors. The authors then go on to suggest that it is best to exercise before 7 AM, avoid peak traffic conditions and avoid major urban roadways.

3. Is there a limit to how much you should exercise when the AQI is high?

One study [5]  has addressed the “tipping point” and the “break-even point” concepts, where the beneficial effects of PA are balanced out by the harmful effects of air pollution (tipping point) or negated (break-even point).

The authors present a model with a sliding scale, where after 70 minutes of walking, or 30 minutes of cycling in a > 300 AQI environment, the tipping point is reached. This would translate to around 40 minutes of running.

So what does this mean for you and I? Any PA is better than none, irrespective of the AQI. However, at AQI levels of above 300, it is best to restrict the PA to moderate amounts, both in terms of time and vigorousness of the activity (e.g. not more than 30-40 minutes of slower running than usual or 60-70 minutes of walking), preferably in the morning and as far as possible on side-roads, away from busy main roads and highways. Indoor PA may be better, perhaps every other day, if there are ways to reduce the indoor air pollution with air filters, otherwise it makes no difference whether you exercise indoors or outdoors in high AQI environments. A little common sense also helps when there are no definitive guidelines.

Footnotes

1. Rajagopalan S, Narula J. The Perils of Anthropogenic Air Pollution: When All Roads Led to Rome. J Am Coll Cardiol. 2022 Nov 8;80(19):1829-1832.

2. Chen R et al. Hourly Air Pollutants and Acute Coronary Syndrome Onset in 1.29 Million Patients. Circulation. 2022 Jun 14;145(24):1749-1760.

3. Guo C et al. Effects of air pollution and habitual exercise on the risk of death: a longitudinal cohort study. CMAJ. 2021 Aug 16;193(32):E1240-E1249.

4. Gupta SK, Elumalai SP. Size-segregated particulate matter and its association with respiratory deposition doses among outdoor exercisers in Dhanbad City, India. J Air Waste Manag Assoc. 2017 Oct;67(10):1137-1145.

5. Tainio M et al. Can air pollution negate the health benefits of cycling and walking? Prev Med. 2016 Jun;87:233-236.

Table of Contents

The Guide * The Atmasvasth Guide to Living Long, Healthy - 15 Aug 2021 Understanding the Steps and Taking Control Taking Control * Atmagyan, Atmasurakshit, Atmanivaaran and Atmanirbar - the four Atmas to be Atmasvasth - 16 May 2021 * The Healthy 7 is also the Happy 7 - 13 Mar 2022 * Prev…

AtmasvasthBhavin Jankharia

The Atmasvasth Guide to Living Long, Healthy

The premise of Atmasvasth is that we can control our health, lengthen our healthspan and lifespan, and be atmasvasth, on our own, with just a little help, if at all, from doctors and the healthcare system. The very first article that I published last December explains this in detail. The

AtmasvasthBhavin Jankharia