The role of physical activity in preventing the risk of death from cardiovascular diseases, cancer, and all causes significantly weakens at particulate matter concentrations above 25 micrograms per cubic meter. As reported in the journal BMC Medicine, at higher particulate matter levels, the effect of physical activity is even more significantly reduced, particularly with regard to the risk of death from cancer.
Physical activity reduces the risk of developing and dying from cardiovascular diseases and cancer. However, people often exercise outdoors, which also exposes the body to fine particulate matter (PM2.5) with a diameter of 2.5 micrometers or less. Long-term exposure to PM2.5 is known to be associated with the development of various health conditions, from systemic lupus erythematosus to breast cancer and dementia. In 2021, high concentrations of PM2.5 in the air were responsible for 4.48 million deaths from cardiovascular disease worldwide.
The idea that the beneficial effects of physical activity on the risk of all-cause mortality, cardiovascular disease, and cancer mortality may be offset by exposure to PM2.5 has been around for some time. However, the sheer volume of data obtained from prospective cohort studies has not allowed for definitive confirmation of this hypothesis.
A team of scientists led by Li-Jung Chen of the National Taiwan Sport University conducted a systematic review and meta-analysis of studies examining the independent or combined association of physical activity and PM2.5 air pollution with all-cause mortality in adults. The analysis included seven cohort studies with a total sample size of 1,515,094 participants, an average follow-up period of 12.3 years, and 115,196 deaths.
The primary analysis showed that higher levels of physical activity were associated with a reduced risk of death from cardiovascular disease, cancer, and all causes. However, this effect was weakened in regions with higher PM2.5 levels. Subgroup analyses showed that moderate-intensity physical activity lasting 150–300 minutes per week was associated with a reduced risk of death by approximately 30 percent at PM2.5 concentrations less than 25 micrograms per cubic meter. The effect decreased by approximately 15 percent at PM2.5 concentrations greater than 25 micrograms per cubic meter (p < 0.001). Compared with the lowest PM2.5 level (less than 10 micrograms per cubic meter), the role of physical activity did not change significantly across the PM2.5 concentration range from 10 to 25 micrograms per cubic meter. The authors separately analyzed the results of three cohort studies with a total sample of 869,038 people who were followed for an average of 11.29 years. It turned out that here too, the protective effect of physical activity significantly decreased at PM2.5 levels above 25 micrograms per cubic meter. At concentrations of 35–50 micrograms per cubic meter, the effect of physical activity became insignificant in most subgroups, particularly with respect to the risk of cancer death. The study's authors believe these results should be interpreted with caution due to the fact that most of the included studies were conducted in high-income countries. Furthermore, physical activity levels were assessed inconsistently across studies and relied on self-reporting. The researchers plan to address these shortcomings in the future. We previously reported that women exposed to air pollution before egg retrieval for IVF significantly reduced the likelihood of a live birth following a subsequent frozen embryo transfer.
