Regular physical activity (PA) can reduce the risk of developing several chronic diseases, including cardiovascular disease (CVD), and also reduces the risk of early mortality (U.S. Department of Health and Human Services, 2008; Physical Activity Guidelines Advisory Committee, 2008). PA is often categorized into four domains based on the location or purpose of activity, including leisure, domestic, occupational, and transportation (Craig et al., 2003; World Health Organization). Active transportation (AT) is defined as any self-propelled human-powered mode of transportation, which primarily includes walking or bicycling. AT is increasingly recognized as one of many ways individuals can achieve recommended PA levels outlined in the 2008 National PA Guidelines (U.S. Department of Health and Human Services, 2008; United States Department of Health and Human Services, 2015; U.S. Department of Health and Human Services, 2015; Centers for Disease Control and Prevention, 2011), which encourage adults to engage in ≥150 min of moderate-intensity PA per week (Physical Activity Guidelines Advisory Committee, 2008; Furie and Desai, 2012).

To promote population-based AT, several national initiatives and priorities have recently emerged (U.S. Department of Health and Human Services, 2008; United States Department of Health and Human Services, 2015; U.S. Department of Health and Human Services, 2015; Centers for Disease Control and Prevention, 2011). These include, but are not limited to, AT-related objectives that are outlined in Healthy People 2020, such as PA-13 (Increase the proportion of trips made by walking) and PA-14 (Increase the proportion of trips made by bicycling), and the 2015 Surgeon General’s Call to Action to Promote Walking and Walkable Communities (United States Department of Health and Human Services, 2015; U.S. Department of Health and Human Services, 2015). The Surgeon General’s report promotes walking across multiple PA domains, including transportation, and encourages communities to improve access to safe and convenient places to walk, bike, use a wheelchair, and be active in other ways (U.S. Department of Health and Human Services, 2015). In 2016, the U.S. Community Preventive Services Task Force determined there was sufficient evidence on the association between the built environment and AT to recommend built environment strategies to improve pedestrian and bicycle transportation systems, and land use and environmental design interventions to encourage PA (Centers for Disease Control and Prevention, 2017a). Despite these national initiatives and priorities to promote AT among individuals and in communities, data from various national surveillance systems have demonstrated inconsistent trends in the prevalence of AT among adults (Whitfield et al., 2015).

Few studies to date have described the health benefits of AT among U.S. adults (Furie and Desai, 2012; Gordon-Larsen et al., 2009; Boone-Heinonen et al., 2009). To our knowledge, only one study has reported significant associations between AT and measured CVD risk factors (Furie and Desai, 2012). Using nationally representative data from 2007 to 2010, the investigators found that adults engaging in AT had lower odds of hypertension and diabetes. Additionally, adults engaging in AT had a lower body mass index (BMI) and smaller waist circumference (Furie and Desai, 2012).

However, it is unknown whether national initiatives and priorities implemented over the past several years have influenced the uptake and prevalence of AT. Furthermore, the associations between AT and CVD health previously reported could be examined with a wider array of measured outcomes (Furie and Desai, 2012). The objectives of this study were to (1) describe the prevalence of and assess trends in AT among adults (≥20 years) using data from the National Health and Nutrition Examination Survey (NHANES) over five cycles (2007–2008, 2009–2010, 2011–2012, 2013–2014, and 2015–2016) and (2) to comprehensively examine the associations between AT levels and measured CVD risk factors from the most recent NHANES cycles (2011–2016).

The NHANES is a nationally representative survey of the U.S. civilian, non-institutionalized population with a complex, multistage sampling design. Since 1999, NHANES has operated continuously and data are released in 2-year cycles. Participants completed in-home interviews and physical examinations in a mobile examination center. NHANES was approved by the National Center for Health Statistics (NCHS) Research Ethics Review Board and written informed consent was obtained from participants. Additional details are available elsewhere (Centers for Disease Control and Prevention, 2012; Centers for Disease Control and Prevention, 2014).

Fig. 1 presents AT prevalence among adults aged ≥20 years who were interviewed in the 2007–2016 NHANES cycles and responded affirmatively to engaging in at least 10 min of AT in a typical week. For adults engaging in at least 10 min of AT in a typical week, the prevalence of high AT (≥150 min/week) increased from 13.1% in 2007–2008 to 17.9% in 2011–2012, and then decreased in 2015–2016 to 10.6%, suggesting a statistically significant quadratic trend (p = 0.004), or a nonlinear trend in the data over time (e.g., change in direction). No significant trend for low AT was observed (p = 0.069 for quadratic trend).

Table 1 presents descriptive characteristics of U.S. adults aged ≥20 years who were examined in the most recent NHANES cycles (2011–2016) by AT level. The majority of adults (74.4%) did not walk or bike for > 10 min for transportation in a typical week, 11.4% engaged in low AT levels, and 14.3% engaged in high AT levels. Compared to the percentages of adults who reported no AT, higher percentages of adults who engaged in low and high levels of AT were younger, male, reported a race/Hispanic origin other than non-Hispanic white, less educated, lower income, were current smokers, met national PA guidelines from non-transportation PA, and resided in urban areas. The prevalence of CVD risk factors—hypertension, hypercholesterolemia, low HDL cholesterol, diabetes, and obesity—generally decreased with increasing AT level.

Table 2 presents the unadjusted and adjusted results from the multivariable logistic regression models examining the associations between AT level and each CVD risk factor. Adjustment attenuated observed associations for all CVD risk factors, except low HDL cholesterol. While attenuated, the adjusted associations between high AT levels and all CVD risk factors remained significant. Most of the adjusted associations between low AT levels and the CVD risk factors also remained significant, except for hypercholesterolemia and obesity. After adjustment for all covariates, compared to reporting no AT, engaging in high AT levels was inversely associated with most CVD risk factors including hypertension (aOR = 0.84, 95% CI 0.71, 0.99), hypercholesterolemia (aOR = 0.79, 95% CI 0.64, 0.97), low HDL cholesterol (aOR = 0.70, 95% CI 0.58, 0.85), diabetes (aOR = 0.69, 95% CI 0.56, 0.84), and obesity (aOR = 0. 66, 95% CI 0.58, 0.76). Compared with no AT, low AT was associated with a decreased odds of hypertension (aOR = 0.77, 95% CI 0.64, 0.91) and diabetes (aOR = 0.68, 95% CI 0.54, 0.85).

The current study described AT prevalence and trends, and examined associations between AT level and a comprehensive set of CVD risk factor measures among a national representative sample of adults aged 20 years and over. Despite the increased attention to AT from several national initiatives implemented or sustained in the past few years (United States Department of Health and Human Services, 2015; U.S. Department of Health and Human Services, 2015; Centers for Disease Control and Prevention, 2017a), we observed a quadratic trend in the prevalence of high AT, with a peak prevalence in 2011–2012, followed by a decline through 2015–2016, which resulted in lower levels to those observed in the beginning of the study period. In an evaluation of AT surveillance data through 2012 across multiple national household health and transportation surveys that utilize a variety of AT measures, AT prevalence from 2007 to 2012 was relatively stable across these varying data sources. This evaluation also included data from NHANES 2007–2012, which was the only data source that showed an increase in 2011–2012 (Whitfield et al., 2015). However, our analysis showed that this increase in 2011–2012 was not sustained and that prevalence of high AT, as measured by NHANES in 2007–2008 and 2015–2016, was similar. In addition to the Call to Action to Promote Walking and Walkable Communities by the Office of the Surgeon General of the U.S. Department of Health and Human Services (U.S. Department of Health and Human Services, 2015), other national multisectoral efforts were made during the current study’s time period to promote AT. The Federal Highway Administration developed a Strategic Agenda for Pedestrian and Bicycle Transportation, which aimed to guide federal pedestrian and bicycle activities (Federal Highway Administration, 2016). In 2016, an update to the National Physical Activity Plan was released by a coalition of organizations across nine sectors to promote walking and walkable communities through crosssector collaborations (National Physical Activity Plan, 2016). The extent to which these previously reported national efforts contributed to the observed trends in this analysis is not known, and more research may be needed to evaluate the effectiveness of national initiatives that promote AT (Centers for Disease Control and Prevention, 2017b).

As with other studies, our results suggested that engaging in AT was more prevalent among adults reporting certain demographic characteristics, specifically adults who were younger, male, Hispanic or non-Hispanic black, within lower education or income groups, meeting PA guidelines through other domains, and residing in urban areas (Furie and Desai, 2012; Whitfield et al., 2015). Continued surveillance of AT over time, using consistent measures, and among diverse population subgroups may inform initiatives to increase AT uptake (Whitfield et al., 2015). Additional surveillance and research may also be needed to monitor neighborhood and environmental features that can support increased AT uptake across these varied population subgroups (U.S. Department of Health and Human Services, 2015; Centers for Disease Control and Prevention, 2017b; Fulton et al., 2016).

Few studies exist that have examined the associations between AT and CVD risk factors among U.S. adults (Furie and Desai, 2012; Gordon-Larsen et al., 2009; Berger et al., 2017), and only one study conducted in 2011 utilized objective measures to assess CVD risk (Furie and Desai, 2012). Using the most recent nationally representative data, we found that high AT levels were associated with a decreased odds of all of the CVD risk factors assessed, including hypertension, hypercholesterolemia, low HDL cholesterol, diabetes, and obesity. Additionally, compared to no AT, adults who engaged in low AT levels had lower odds of having hypertension and diabetes. Furie and Desai used combined NHANES data from 2007 to 2010 and reported inverse associations between AT and hypertension, diabetes, lower BMI, and waist circumference. In contrast to our study’s findings which demonstrated high AT was associated with decreased odds of low HDL cholesterol, the investigators found no significant associations for low HDL cholesterol (Furie and Desai, 2012). Another study by Gordon-Larsen and colleagues investigated associations between walking or bicycling to work and various measured CVD risk factors and serum measures among young adults aged 18–30 years from Birmingham, Alabama; Chicago, Illinois; Minneapolis, Minnesota; and Oakland, California. They found that active commuting to work was inversely associated with blood pressure, triglyceride levels, insulin level, BMI, and obesity among men (Gordon-larsen et al., 2013). Finally, a study conducted by Berger and colleagues of a convenience sample of adults in Minnesota reported significant associations between bicycling for AT and decreased odds of hypertension and obesity (Berger et al., 2017). While these investigations provide information on the relationships between AT and various CVD risk factors, these studies either did not utilize recent nationally representative data, assessed only younger adults, focused on one mode of AT or only AT for commuting to and from work, or did not adjust for urbanization level. Additionally, some of these studies relied on self-reported measures. Given prior research has demonstrated differences between self-reported and device-based measures when examining associations between total PA and measured CVD risk factors at the national level (Tucker et al., 2016; Atienza et al., 2011), future research may be needed to examine these differences between self-reported and device-based measures of AT and associations with objective CVD outcomes.

The present study’s findings were also consistent with studies published from other countries. In a meta-analysis of eight studies that examined the relationship between active commuting and various CVD risk factors in Europe and Japan (Hamer and Chida, 2008), active commuting demonstrated a protective effect on cardiovascular outcomes, including coronary heart disease (Hu et al., 2007; Wagner et al., 2002), stroke (Hu et al., 2005), hypertension (Barengo et al., 2005; Hayashi et al., 1999), and diabetes (Hu et al., 2003). Similar to the aforementioned studies conducted in the U.S., the studies in the meta-analysis were subject to limitations in that they only considered AT to and from work and did not adjust for urbanization level (Hamer and Chida, 2008).

The current study revealed fluctuating trends in AT prevalence from 2007 to 2016, and inverse associations between AT and certain CVD risk factors in recent years. Despite the potential health benefits and national recommendations that have identified AT as one of many ways individuals can achieve recommended PA levels (U.S. Department of Health and Human Services, 2008; Physical Activity Guidelines Advisory Committee, 2008; United States Department of Health and Human Services, 2015), the majority of U.S. adults do not engage in any AT. After increasing through 2012, the prevalence of high AT has since declined to levels comparable to those in 2007–2008. These results may inform public health research designed to promote AT, such as those outlined in the Surgeon General’s Call to Action to Promote Walking and Walkable Communities (U.S. Department of Health and Human Services, 2015) and the Guide to Community Preventive Services (Centers for Disease Control and Prevention, 2017a).