Researchers at the University of São Paulo analyzed inflammatory markers in cyclists who trained regularly and had been exposed to traffic-related pollution. The results of the experiment, which was conducted in São Paulo city, are published in the American Journal of Physiology (photo: Léo Ramos Chaves/Pesquisa FAPESP)
Published on 08/07/2023
By Karina Ninni | Agência FAPESP – Many recent studies suggest that endurance exercise in polluted environments can have undesirable effects on human health, but this may not be true for people accustomed to traffic-related air pollution, according to an article published in the American Journal of Physiology by members of the Aerobic Performance Research Group at the University of São Paulo’s School of Physical Education and Sports (EEFE-USP) in Brazil.
Also called aerobic exercise, endurance exercise includes activities that strengthen breathing and heart rate, such as walking, jogging, swimming or biking.
The participants in the study were ten male recreational cyclists, most of whom regularly trained on bike paths and the university campus in São Paulo city, where annual levels of traffic-related air pollution measured by CETESB, the São Paulo State Environmental Agency, exceed the ceiling considered tolerable by the World Health Organization (WHO).
In contrast with expectations, the researchers found that inflammation markers in the blood of these cyclists, such as interleukins 6 and 10 (IL-6 and IL-10) were not altered. On the other hand, they detected increased levels of brain-derived neurotrophic factor (BDNF), associated with the benefits of exercise for neuroplasticity, the brain’s ability to change and adapt in response to experience.
Based on these results, the researchers formulated the hypothesis that people who exercise in an environment with high air pollution may adapt to such conditions. This may apply particularly to cyclists in São Paulo city, which is notorious for its high levels of traffic-related pollution. “The benefits of exercise appear to more than offset the adverse effects of air pollution in this case,” said André Casanova Silveira, first author of the article.
Silveira explained that the group started from two studies by Rômulo Bertuzzi, head of the Department of Sports at EEFE-USP and coordinator of the Aerobic Performance Research Group. The studies used a constant-load exercise model and showed an increase in inflammatory markers after 60 minutes. “However, constant-load exercise models don’t evaluate performance, don’t mimic sporting performance well, and are very different from a race or contest. We designed an experiment involving more than 60 minutes of exercise and mimicking a competition,” he said.
The study was supported by FAPESP via a PhD scholarship awarded to Silveira.
“Real” pollution
The experiment was conducted in an environmental chamber located on the parking lot outside the Medical School (FM-USP) on Avenida Doutor Arnaldo in the center of São Paulo city, 20 m from the street and 150 m from a busy intersection. The chamber was designed by a group led by Paulo Saldiva, a professor at FM-USP with whom Bertuzzi collaborates.
The cyclists simulated participation in a 50 km time trial lasting roughly 90 minutes. A time trial (TT) is a road event in which each contestant races alone against the clock. “We put the bike on the rollers and the subject pedaled around a virtual-reality track. It was a simulated competition. They visualized a track on the computer screen. There was a certain amount of pressure so that they felt as if they were pedaling on the street. They could control the intensity and change gears,” Silveira said.
The chamber had two ducts through which air was introduced from outside by a pump, as well as a particulate matter filter and chemical filters to remove formaldehyde, hydrogen sulfide, sulfur dioxide, nitrogen oxide (NO), nitrogen dioxide (NO2) and other toxic gases. “The marker for our study was particulate matter, which is the parameter most used in the literature,” he said.
The cyclists were submitted to two sessions on different days with an interval of at least 48 hours between them. The trials were performed in polluted or filtered air on a randomized basis. “The pollution mimicked actual conditions. Previous research used a diesel engine to mimic pollution, but diesel produces very high levels of particulate matter, and there’s no mixture with anything else. In our case, the pollution came from the street and was real,” Silveira said.
All trials were performed in controlled temperatures ranging from 20 °C to 24 °C and took place two hours after the cyclist’s last meal. Data collection occurred in 2019, before the COVID-19 pandemic, between 10 a.m. and 4 p.m. Inflammatory markers (IL-6, C-reactive protein or CRP, IL-10 and intercellular adhesion molecule –1, or ICAM-1) and neuroplasticity (BDNF) were measured in blood samples collected before and after completion of each 50 km circuit.
Surprising results
Levels of IL-6, CRP and IL-10 did not differ significantly between the trials performed with and without pollution. In the former, however, BDNF levels rose and ICAM-1 levels fell after exercise. “Higher BDNF levels promote growth and proliferation of cells in the hippocampus [a complex brain structure in the temporal lobe, with a major role in learning, memory and emotion]. BDNF is also involved in neuron differentiation, plasticity, cell survival and learning. The increased BDNF levels we detected in the polluted environment were the most surprising result of our study. Exercise is supposed to suppress expression of this protein, according to the literature. In future research, we plan to conduct cognitive tests, in addition to measuring BDNF, in order to find out whether exposure to pollution correlates with performance and cognition, as we haven’t investigated this correlation yet,” Silveira said.
ICAM-1 plays a critical role in mediating the firm adhesion of leukocytes (white blood cells) to endothelial cells in various inflammatory diseases. “ICAM-1 increases at the start of an inflammatory process because it helps macrophages [immune system cells] adhere to damaged cells. It’s an early inflammation marker, indicating the onset of an inflammatory state,” Silveira said. “In our experiment, if we’d observed an increase in inflammation due to pollution, ICAM-1 could have been more expressed in the trial performed in the polluted environment, but that wasn’t the case. There’s little in the literature for us to be able to discuss ICAM-1 and the results relating to it so far.”
The research group assumed the cyclists’ performance would deteriorate because in a polluted environment, effort seems to increase in terms of subjective perceptions. “In a competitive setting, participants control the intensity of the exercise through their subjective perceptions of effort and make adjustments during the trial on this basis. I expected perceived effort to increase and performance to decrease in the polluted environment owing to the subjective symptoms of pollution, such as sore eyes and runny nose, but this wasn’t the case,” Silveira said.
“Another surprising point was the behavior of inflammatory markers. Previous research by our group showed an increase in these markers after 60 minutes. We therefore expected an increase in a lengthy time trial, which was more intense than constant-load cycling. The lack of difference between the markers in these situations was a surprise.”
The main finding from the study, he added, was that exercise is beneficial even in polluted conditions provided the practitioner has adapted to this kind of environment. “In my postdoctoral research, for which I recently submitted a proposal, I plan to make a distinction between groups with more and less exposure to pollution. I want to compare them in order to see whether the level of prior exposure affects inflammation, cardiovascular adaptation and the other effects of exercise,” he said.
The article “Effects of air pollution exposure on inflammatory and endurance performance in recreationally trained cyclists adapted to traffic-related air pollution” is at: journals.physiology.org/doi/abs/10.1152/ajpregu.00305.2021.
Source: https://agencia.fapesp.br/42084
