Today we are going to focus on … and the implications for obesity.
Start by focusing on study by Addy and colleagues.Was very micro in its focus. Looked at neighborhood characteristics. Researchers looked at…
Also looked at …So, they looked a little bit broader, but basically the focus was fairly small.
They wanted to see whether or not these physical features were associated with how physically active people were. So, not at their obesity or overweight risk per se, but rather if these physical features were associated in any way with how much time people spent being physically active. They looked at two different measures, the first was to look at how physically active people were measured by whether or not they spent 30 minutes or more on 5 days or more per week being physically active. Jogging, biking, walking, and if they did spend 30 minutes or more on 5 or more days per week, which is the CDC’s recommendation, then they were deemed to be active. They were coded as being insufficiently active if they were physically active, but perhaps for fewer than 5 days a week, or for a period of time that lasted less than 30 minutes. They were coded as being inactive if they had no moderate or vigorous physical activity.They also looked at a separate measure which was whether or not people said they were regular walkers, that is that they walked for 30 or more minutes 5 days a week. Irregular walkers were those who walked, but at a lower frequency, and non walkers were those who reported walking for no more than 10 minutes at a time through the course of a week.
What they found was…So,Addy and colleagues findings show that there is some association between neighborhood characteristics and being physically active at the micro level.
Were interested not in looking at physical activity, but whether the larger community environment affects the risk of being overweight or obese. So, they pointed to urban sprawl as perhaps being a culprit that was contributing to the rise in obesity rates.
How do the physical features in the communities in which we live affect our risk of overweight and obesity? Well, this is a question that some people here in the department have been looking at for several years now, and so we will talk a little about a study that they published in 2008, that was not part of your reading, but will serve as a background for the last study that is on your reading list. Didn’t know who people were, but knew characteristics of what the neighborhoods were like.
Had neighborhood characteristics that they thought reflected the 3 D’s that we have already talked about. With more intersections, they thought this would be a neighborhood where there would be more opportunities to walk and people would have lower BMI’s and lower rates of obesity.
This map shows the geographic variation in body mass indices across census block groups. There are little more than 500 census block groups within Salt Lake County. What is shown here is that generally speaking, on the East side, there is lower average BMI, and on the West Side of the county there is generally higher BMI, but there is a lot of variation even within those general statements. There are Higher BMI areas that are in the central part of the county, and lower BMI areas that are on the West as well. This map was constructed for both men and women together, but you can see in the lower right corner, that the overall mean BMI for men was … and for women it was … Now these are probably on the low side or are more conservative estimates of BMI because height and weight as reported on driver’s licenses is self reported, and especially women tend to underreport their weight, and men tend to overreport their height, which would lead the to be more conservative estimates. To give you a sense of what a number like 25.01 means, if you took a woman who was 5ft 3 inches tall and weighed 130 pounds, she would have a BMI of 23.2. so that should give you some sense then that the average resident of Salt Lake County, adults between the ages of 25 and 64, has a BMI that is on the border or slightly over the border between normal weight and overweight.
This slide shows the variation in obesity rates across Salt Lake County, and again, not surprisingly, you see the same type of pattern that we saw on the last slide. This groups together both men and women, … Statewide, obesity rates for Utah in 2005 was just under 22%, so Salt Lake county tends to be a little less likely to be obese than the state as a whole.
The multivariate analysis that they did looked to see if once you controlled for the socio-demographic characteristics of the neighborhood such as the median income level of the neighborhood and the racial- and ethnic composition of the neighborhood, did the physical features of the neighborhood affect the likelihood of being overweight? What can be seen in this graph is that controlling for all of the socio-demographic characteristics, that the odds of being overweight … the odds of being overweight goes up for both men and women, and it goes up for all 4 age groups that were looked at. So for even the youngest age group, age 25-34, if they live in a neighborhood with newer housing compared to a neighborhood with older housing, the odds of being overweight increases and the storyline here is that older neighborhoods tend to be neighborhoods that are more likely to have sidewalks, mixed land use, old trees that provide shade and are pleasant to look at. Newer neighborhoods are much less likely to have sidewalks, mix land use, and they are less likely to have the trees and other amenities that might invite people to be more physically active.
This shows what happens to the odds of… So this isn’t I say I walk to work and here is my BMI, they did not make that link, but rather, on average, for a block group, what fraction of the adults in the census reported that they walked to work. They then used this number to relate to individual BMI’s for people who lived in that block group. Again, here there is a pattern that for both men and women across age ranges, that as there is a decrease of the fraction of people who say they walk to work within a block group, there is an increase in the risk of being overweight. As an example, for a 35 to 44 year old female, the odds of being overweight go up to about 1.45 so about 45% more likely to be overweight than her counterpart that lives in a block group where 10% more of the people say that they walk to work. The effect seems to be a little lower for males, but they are also positive, again, if you focus on the 35-44 age group, you see that the odds of being overweight go up by about 28% for males if they live in a block group where 10% fewer people walk to work compared to an otherwise similar male who lives in a block group where 10% more of the population report walking to work. Again, walking to work is an indication of land use diversity, that means that there must be commercial destinations as well as residential destinations within the block group, and therefore there are more opportunities or more enticements to get people out and walking to work.
Finally, the other generally, but not completely consistent finding that they had was the impact of intersection density. They were measuring the number of intersections within a quarter mile radius of the resident’s home and here what can be seen is that for ll age groups and for most cases both men and women, but not always, as the number of intersections within a quarter mile radius is increased, the likelihood that they will be overweight is decreased,. As the number of intersections is decreased, the odds of being overweight are increased. This is a 10 point change in intersections, so the magnitude of effects for the intersection density are certainly much smaller than the magnitude of the effects for the percentage of people who walk to work, or the median year in which housing was built, but it still did have an effect. This is reflecting design, that is that neighborhoods that have greater intersection density may promote walkability because it is easier to get from point A to point B, and that is what Smith and colleagues found in their analysis.
What are the key findings within the literature that focuses on the physical environment and the promotion of physical activity that might reduce the risk of overweight and obesity? If you think about this in the context of the growing trends of greater overweight and obesity, you also have to think about… starting in the 1950;s and 1960’s, there was a move away from designs with high population density, high street connectivity, sidewalks, things of that sort, to the suburban design where there was very little land use diversity, there weren't’ always sidewalks or good street connectivity, and so the communities that have been built over the last 30, 40, maybe 50 years, are communities that don’t necessarily promote physical activity to the extent that older communities like the downtown areas within Salt Lake City, like Sugarhouse. We have been looking at energy expenditures, but we haven’t really looked at energy intake and the fact that there is a 7-11 with Big Gulps on many street corners these days. So, in the last lecture, we are going to focus on food environment.
Community Design and Physical Activity
Community Design Study by Addy et al. 2004 Data from predominantly rural south-eastern county Neighborhood characteristics Sidewalks Public recreation facilities Streetlights Pleasant walking Physically active neighborhood Traffic volume Unattended dogs Crime Perception of neighbors being untrustworthy
Community Characteristics Walking/bike trails Swimming pools Recreation facilities Parks Playgrounds Sports fields Schools Malls Places of worship Waterways Crime and safety concerns associated with recreation facilities
Measurement of Physical Activity Active = 30 minutes or more of physical activity on 5 or more days per week Insufficiently active = lower frequency of physical activity Inactive = no moderate or vigorous physical activity Regular walkers = 30 min. or more 5 days a week Irregular walkers = lower frequency of walking Nonwalkers = no walking for 10 minutes or more at a time
Addy et al. Findings Level of physical activity positively associated with… Street lighting Assessments that neighbors can be trusted Presence of community parks Walking behavior statistically associated with… People being active in the neighborhood Sidewalks Presence of community malls for physical activity
What about measures of the larger physical environment?Ewing et al., 2003 Data from the Behavioral Risk Factor Surveillance System Multivariate analysis that controls for demographic and behavioral covariates Found residents of “sprawl” counties were more likely to… Spend fewer minutes walking Be heavier Have hypertension When compared to otherwise similar residents of compact counties
What about here in Salt Lake?Smith et al., 2008 Research Question: Are less “walkable” neighborhoods associated with greater risk of adults (25-64) overweight? Study Population: Salt lake County, 2005, N=243,330 Men and 223,552 Women Data Source: Utah Population Database (UPDB) that holds de-identified information on all persons with a Utah Driver License and 2000 U.S. Census. UPDB holds data on residential address and height/weight derived from Driver License information. All addresses were converted to UTM coordinates & linked to 2000 Census block groups.
Measures of Neighborhood Walkability – 3D’s Higher Population Density: measured by population per square mile More Diversity of Destinations: measured by Median age of housing in the neighborhood The proportion of adults who walk to work More Pedestrian Friendly Designs: measured by intersections in ¼ mile radius of residence
Odds of Overweight for a 10 Year Increase in the Median Year in Which Homes were Built (Newer Homes) in a Block Group
Odds of Overweight for a 10 Point Decrease in the Percent of Working-Aged Adults in the Block Group Who Walk to Work
Odds of Overweight for a 10 Point Decrease in the Number of Intersections in a ¼ mile radius of the Resident’s home
Reviewing… Growing evidence that a community’s physical features may affect energy expenditures What has the design of new communities looked like over the past few decades? In Salt Lake County lower risk of obesity/overweight are associated with Greater diversity of destinations (as measured by housing age and % who walk to work) Design features that might promote walkability- higher intersection density. But what about the role of the food environment?