Our study has several limitations
Our study has several limitations and assumptions. RR estimates for the association between physical activity and cancer in the Brazilian population are inexistent. We used RR derived from a recent dose-response meta-analysis using data from cohort studies conducted mainly in US and European countries. These estimates might not be applicable to Brazil, especially if the prevalence of effect modifiers differs between settings []. Some RR estimates included in this meta-analysis were adjusted by body mass index. Therefore, our preventable fractions estimates are likely to be underestimated by not considering the overall effect of physical activity mediated through adiposity, which is an established risk factor for breast and colon cancers [61,62].
In our study, physical activity level was self-reported and therefore misclassification may have occurred. However, the PNS questionnaire showed reasonable reliability and validity compared to the Global Physical Activity Questionnaire, a validated questionnaire for physical activity surveillance recommended by the WHO . Participants were asked about frequency and duration of physical activity in a typical week, but the questionnaire did not include information about intensity of activities. To define intensity of activities, we used a standard method by applying MET (Table S1) related to each domain of physical activity as described in the 2011 compendium of physical activities . Questionnaires assessing physical activity level in the typical week tend to overestimate total NPS-2143 expenditure compared to objective-measures (e.g., doubly labelled water) . Therefore, our estimates of preventable fractions due to physical activity may be underestimated. We used prevalence data from the most recent representative population-based survey conducted in Brazil in 2013, assuming that trends of physical activity have remained unchanged over time. In fact, leisure-time physical activity slightly increased in the 27 federative units in Brazil over the past few year, while a decrease in transportation physical activity was also observed . Whether these changes affected total physical activity level in the whole country remains unknown and a matter of future studies.
Authorship contribution statement
Funding Leandro Fórnias Machado de Rezende receives a doctoral scholarship from Sao Paulo Research Foundation (FAPESP), grant #2014/25614-4 and #2016/21390-0. Leandro Martin Totaro Garcia has undertaken this work under the auspices of the Centre for Diet and Activity Research (CEDAR), a UKCRC Public Health Research Centre of Excellence which is funded by the British Heart Foundation, Cancer Research UK, Economic and Social Research Council, Medical Research Council, the National Institute for Health Research, and the Wellcome Trust.
Conflict of interest
Introduction According to the World Health Organization (WHO), there were approximately 3.7 million deaths attributable to environmental air pollution in 2012, 88% of those deaths occurring in low- or middle-income countries and approximately 6% being from lung cancer . In an estimate of the patterns of cancer incidence and mortality in 40 European countries in 2012, lung cancer was found to be the fourth most common type of cancer, with 410,000 new cases, and the leading cause of death from cancer, with 353,000 deaths . According to the Brazilian National Cancer Institute, there were an estimated 17,330 and 10,890 new cases of tracheal, bronchial, or lung cancer among men and women, respectively, in Brazil in 2016, corresponding to an estimated incidence of 17.49 cases/100,000 men and 10.54 cases/100,000 women . Although smoking is considered a potential risk factor for lung cancer, exposure to environmental carcinogens has been associated with the occurrence of the disease. The International Agency for Research on Cancer (IARC) has stated that there is strong evidence that diesel engine exhaust is carcinogenic to humans, therefore classifying its constituents as Group 1 carcinogens . The IARC subsequently concluded that exposure to elevated levels of outdoor air pollution, especially particulate matter, increases the risk of lung cancer, being both classified as carcinogenic to humans (Group 1) .