Urban greenness and physical activity in a national survey of Canadians

Recent research suggests that urban greenness has important beneficial effects on health. While some epidemiological studies have investigated associations between measures of greenness and participation in physical activities, the findings have been inconsistent and several have relied on self-reported rather than objectively determined measures of greenness. Further, there have been few national studies. Our aim was to characterize associations between residential measures of greenness and physical activity within a nationally representative sample of Canadians. Moreover, we sought to determine to what extent these associations were modified by age, sex and income. Our analyses are based on data collected from participants of the 2001 Canadian Community Health Survey. Analyses were restricted to 69,910 individuals who were: 20 years of age and older, lived in urban areas, and for whom a residential measure of greenness could be assigned. The Normalised Difference Vegetation Index (NDVI), which is an objectively defined measure of greenness based on satellite imaging, was assigned to the residential addresses of the participants. Our NDVI values were based on 30 m and 500 m buffers from the centroid of the provided postal codes. Logistic regression was used to estimate odds ratios (ORs) and their 95% confidence intervals to describe associations between greenness and several measures of physical activity. The ORs were adjusted for age, sex, smoking status, marital status, and income. We found that participants who resided in the highest quartile of greenness, based on a 500 m buffer, were more likely to participate in leisure-time physical activity (adjusted OR=1.34, 95% CI=1.25-1.44) when compared to those in the lowest quartile. Positive associations were observed between greenness and physical activity in all income groupings. A key finding was the observation of a stronger association between greenness and measures of physical activity among younger adults, especially women. Our findings have important public health implications as they suggest that access to urban green environments contributes to increased participation in leisure-time physical activity which has demonstrable health benefits.