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Neighbourhood greenspace and physical activity and sedentary behaviour among older adults with a recent diagnosis of type 2 diabetes: a prospective analysis
  1. Shanley Chong1,2,
  2. Soumya Mazumdar1,2,
  3. Ding Ding3,
  4. Geoff Morgan3,
  5. Elizabeth Jean Comino4,
  6. Adrian Bauman3,
  7. Bin Jalaludin1,5
  1. 1 Population Health, South Western Sydney Local Health District, Liverpool, New South Wales, Australia
  2. 2 South Western Sydney Clinical School, University of New South Wales, Sydney, New South Wales, Australia
  3. 3 Faculty of Medicine and Health, University of Sydney, Sydney, New South Wales, Australia
  4. 4 Centre for Primary Health Care and Equity, University of New South Wales, Sydney, New South Wales, Australia
  5. 5 School of Public Health and Community Medicine, University of New South Wales, Sydney, New South Wales, Australia
  1. Correspondence to Professor Bin Jalaludin; Bin.Jalaludin{at}health.nsw.gov.au

Abstract

Objectives Greenspace is one of the important factors that can promote an active lifestyle. Thus, greener surroundings may be a motivating factor for people with newly diagnosed diabetes to engage in more physical activity. Given that diagnosis of type 2 diabetes (T2D) may serve as a window opportunity for behavioural modification, we hypothesise that the association between neighbourhood greenspace and physical activity among people with newly diagnosed T2D may be greater than those not diagnosed with T2D. The aim of this study was to investigate the association between access to greenspace and changes in physical activity and sedentary behaviour, and whether these associations differed by T2D.

Design Prospective cohort.

Setting New South Wales, Australia.

Methods We used self-reported information from the New South Wales 45 and Up Study (baseline) and a follow-up study. Information on sitting, walking and moderate to vigorous physical activity was used as outcomes. The proportion of greenspace within 500 m, 1 km and 2 km road network buffers around participant’s residential address was generated as a proxy measure for access to greenspace. The association between the access to greenspace and the outcomes were explored among the newly diagnosed T2D group and those without T2D.

Results Among New T2D, although no significant changes were found in the amount of walking with the percentage of greenspace, increasing trends were apparent. There was no significant association between the percentage of greenspace and changes in amount of moderate to vigorous physical activity (MVPA). Among No T2D, there were no significant associations between the amount of MVPA and walking, and percentage of greenspace. For changes in sitting time, there were no significant associations with percentage of greenspace regardless of buffer size.

Conclusions In this study, there was no association between access to greenspace at baseline and change in walking, MVPA and sitting time, regardless of T2D status.

  • physical activity
  • diabetes
  • green space

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Strengths and limitations of this study

  • This is the first study to explore environmental influences on the behaviours of people who transition into living with type 2 diabetes (T2D), and compare its association with those without type 2 diabetes .

  • This is a large population-based cohort with data available at two time points.

  • A limitation is that the change in duration of physical activity and sitting were calculated from self-reported surveys.

Introduction

Type 2 diabetes (T2D) is a lifelong condition and is associated with increased risk for cardiovascular, renal disease1 and mortality.2 3A healthy lifestyle that includes, for example, regular physical activity, can help maintain healthy blood glucose levels and reduce the risk of complications of T2D.4–7 However, only about half of Australians with diabetes achieve adequate control of their blood glucose level.3

It is recommended that adults, including those diagnosed with T2D engage in at least 30 min of physical activity every day.8 In a population-based study in Australia, participants with incident T2D reported lack of changes in their walking and moderate to vigorous physical activity (MVPA) after their diagnosis. Studies reported that 60% of people aged 35–64 years with diabetes (types 1 and 2) were not achieving the recommended level of physical activity,9 one third of adults with T2D were completely inactive10 and only a third exercised on regular basis.10 Physical activity behaviour is determined by a range of biological, psychosocial and environmental factors.11 Built environment attributes are frequently found to be associated with physical activity,12 and activity-unfriendly environments may be associated with higher T2D incidence.13 For example, a study reported that one of the barriers among inactive patients with diabetes (both type 1 and 2) was lack of local facilities.14

One environmental attribute that plays an important role in physical activity is greenspace.15–17 Greenspace is defined as any vegetated land adjoining an urban area which includes bushland, nature reserves, national parks, outdoor sports fields, school playgrounds and rural or semi-rural areas immediately adjoining an urban area.18 Several studies have found that people who have better access to parks and green spaces are more likely to report that they engage in physical activity.19 20 The potential mechanism for these associations may be that greenspace prompts, facilitates, and reinforces location-specific physical activity,21 while simultaneously discouraging sedentary lifestyles. Thus, greener surroundings may be a motivating factor among people with newly diagnosed diabetes to engage in more physical activity. Given that diagnosis of T2D may serve as a window opportunity for behavioural modification,22 23 we hypothesise that the association between neighbourhood greens pace and physical activity among people with newly diagnosed T2D may be greater than those never diagnosed with T2D.

Using data from a large cohort study in New South Wales (NSW), Australia, we aimed to investigate the associations between the access to neighbourhood greenspace and changes in physical activity and sitting time by T2D diagnosis status.

Materials and method

Study population

The study area was the Sydney Statistical Division (figure 1A) which has a population of approximately 4.12 million people and covers an area of 12 428 km2. It is the largest urban agglomeration in Australia, with a wide range of environmental features and diverse sociodemographic characteristics.

Figure 1

Sydney statistical division (A) and 500 m polygon-based network buffer (B).

Information about physical activity and relevant covariates at the individual level was obtained from the baseline 45 and Up Study and the follow-up Social, Economic and Environmental Factors (SEEF) Study. The 45 and Up Study is a population-based cohort survey of NSW residents aged 45 years and older. Recruitment was undertaken between 2006 and 2009. Potential participants were randomly selected from the Medicare Australia database (Australia’s universal public health insurance system). Participants joined the study by completing a mailed self-administered questionnaire and providing consent for long-term follow-up, including linkage to various personal health records. The response rate was 18% and participants comprised 11% of the NSW population aged 45 years and over.24 The full study cohort consists of 267 153 people aged 45 years or older at the time of recruitment.

In 2010, the SEEF Study questionnaire was distributed to the first 100 000 participants of the 45 and Up Study, of whom 60 404 returned the completed questionnaire. The average follow-up period was 3.3 ± 0.9 years (median=2.8 years, IQR=2.6–4.6 years). Questionnaires for both the 45 and Up and the SEEF Study are available from the Sax Institute website. Of the 60 404 participants, 24 220 resided in the study area at the time of the baseline 45 and Up Study.

Measures

Exposure: access to greenspace

We used the percentage of greenspace within 500 m, 1 km and 2 km polygon-based road network (PBRN) buffers (figure 1B) around participants’ residences (available for the baseline survey only) as proxies for geographic access to greenspace. These buffer sizes were chosen as they are considered as walkable distance.25

Greenspace data were obtained from StreetPro (PitneyBowes, North Sydney, Australia). In this dataset, greenspace includes national parks, nature reserves, historic sites, state forests, State recreation areas, wildlife refuges, conservation parks, protected areas, wildlife reserves, urban recreation parks and other urban greenspaces. The PBRN buffers were created using the StreetPro Navigation (PitneyBowes) road network file and ArcGIS network analyst to calculate the endpoints of all possible routes up to the specified distance (500 m, 1 km and 2 km) along the road network for each participant’s residence. The endpoints were then connected to form irregular polygons. Percentage of greenspace within PBRN buffers were categorised into 0%–5%, >5%–10%, >10–15%, >15%–20% and >20%. We combined >15%–20% and >20% for greenspace within 500 m buffers due to the small sample sizes.

Outcomes: duration of sitting and physical activity

Information on sitting (hours per week), walking (minutes per week) and MVPA (minutes per week) was collected in both surveys. Duration of sitting was adapted from the International Physical Activity Questionnaire which has acceptable reliability26 and validity.26 Physical activity was assessed using the Active Australia Survey27 which also has acceptable reliability28 and validity.29 In this instrument, walking is defined as walking for recreation or exercise or to get to or from places. Vigorous physical activity refers to any activity that causes a participant to breathe harder or puff and pant. Moderate physical activity refers to less intense activities such as gentle swimming, social tennis, vigorous gardening or work around the house. Total weighted minutes of MVPA per week is calculated by the sum of minutes of walking, moderate physical activity and twice the minutes of vigorous physical activity.28 Reported time spent on walking and MVPA greater than 14 hours per day was considered as an impossible value and recoded to 14 hours.30 We conceptualised walking and total MVPA as two separate outcomes because walking is expected to be more specifically related to neighbourhood greenspace while total MVPA is commonly used as a measure of overall levels of health-enhancing physical activity.

T2D diagnosis

New cases of T2D were defined as those participants who did not report T2D at the baseline survey but reported T2D at the follow-up survey (New T2D). The comparator group was participants who did not report T2D at both baseline and follow-up surveys (No T2D). The questions asked to determine a diagnosis of T2D at the baseline survey were ‘Has a doctor ever told you that you have diabetes’ and ‘Have you taken Diabex, Diaformin, Metformin for most of the last 4 weeks’.

Participants who reported that they had been told by a doctor that they had diabetes were then also asked about their age at diagnosis. For participants with newly diagnosed T2D, the time lapse since diagnosis to completion of the SEEF Study questionnaire was also calculated (age at time of completion of SEEF Study questionnaire minus age at T2D diagnosis). Self-reported diagnosis of T2D in the 45 and Up Study has high sensitivity (83.7%) and specificity (97.7%) compared with administrative hospitalisation data.31

Covariates

A directed acyclic graph (DAG) was used to identify potential covariates (figure 2), measured at baseline, to predict physical activity and duration of sitting. The list of covariates, reported at baseline, include sociodemographic characteristics (age, gender, country of birth (English-speaking countries, Europe, Middle-East, Asia, Other)) and an area-level deprivation score. Area-level deprivation was measured by the 2006 Index of Relative Socio-Economic Disadvantage (IRSED) quintiles at the postcode level. The IRSED was created by the Australian Bureau of Statistics to compare social and economic disadvantage across geographical areas in Australia. The index is derived from the 2006 Census variables such as income, educational attainment, unemployment and people working in unskilled occupations.32

Figure 2

Directed acyclic graph of the relationship between neighbourhood greenspace and physical activity and sitting. BMI, body mass index.

We also included physical functioning at baseline (measured using the Medical Outcomes Study Physical Functioning Scale; it ranges from 0 to 100 and was categorised into no limitation (100), minor limitation (95–99), moderate limitation (85–94), or severe limitation (0–84)),33 psychological distress at baseline (Kessler-10 (K10); a K10 score of ≥22 reflects high or very high psychological distress34 and body mass index (BMI) at baseline as potential covariates.

As several studies have reported the beneficial effect of greenspace on mental health,35–37 and that poor mental health can impact on physical activity,38–40 we also tested whether psychological distress at baseline could be a potential mediator between neighbourhood greenspace at baseline and changes in physical activity at follow-up (see DAG figure 2).

Similarly, we also tested for BMI reported at baseline as another potential mediator between neighbourhood greenspace at baseline and changes in physical activity at follow-up. Increased greenspace has been associated with reduced weight,41 less weight gain,42 and people are less likely to be obese in greener areas.43 Moreover, people who are overweight or obese reported spending less of time in physical activity than those who are normal-weight.44–46

Statistical analysis

The Kruskal-Wallis test was used to compare continuous baseline lifestyle variables between the two T2D groups. Separate regression models were used to examine the association between neighbourhood greenspace access and change in outcome variables (in MVPA, walking and sitting). To adjust for correlation between participants within local government areas (LGA), generalised estimating equations model was applied. Assuming no specific order between observations in the same LGA, the compound-symmetric correlation structure was used. BMI and psychological distress were tested for mediation between neighbourhood greenspace and physical activity. There were no associations between neighbourhood greenspace and BMI and psychological distress. However, BMI, but not psychological distress, was associated with changes in the outcome variables and therefore included in the final models. Psychological distress was not included in the final models. The final set of variables included in the final models was age, gender, educational attainment, level of physical functional limitation, IRSED, BMI at baseline, and duration of T2D diagnosis (New T2D group only), follow-up time and the baseline value of each outcome in specific models. To examine whether the association between greenspace and change in outcome variables modified by the presence of T2D, a two-way interaction between the status of T2D (New T2D and No T2D) and percentage of greenspace was explored. We then developed regression models, stratified by the presence of T2D. Predicted values of change and associated 95% CIs were reported. To adjust for multiple comparison, Bonferroni method were used in the final models. Statistical analyses were conducted using SAS V.9.4.

Patient and public involvement

Patients and the public were not involved in the design of this study.

Results

Of the 24 220 participants living in Sydney Statistical Division, 628 were excluded due to inconsistent reporting between baseline and follow-up surveys, 1498 were excluded due to reporting T2D at both baseline and follow-up and an additional 4000 were excluded because of severe level of physical function, making physical activity challenging or infeasible, leaving 18 094 participants in the analytical sample (figure 3).

Figure 3

Flow chart of sample selection. SEEF, Social, Economic and Environmental Factors; T2D, type 2 diabetes.

Of the 18 094 participants, 260 (1.4%) reported T2D in the follow-up survey but not in the baseline survey (New T2D) whereas 17 834 (98.6%) participants did not report T2D at both baseline and follow-up (No T2D). The average duration of time since diagnosis was 1.8 ± 1.1 years (median=1.7 years). More than half of all the participants were female (52.0%) and the average age of participants was 59.5 ± 9.6 years. The majority of participants were born in an English-speaking country (85.2%) and about one-quarter had not completed high school education (table 1).

Table 1

Changes in outcome variables at follow-up by baseline characteristics

Table 1 shows changes in outcome variables at follow-up by baseline sociodemographic characteristics and access to greenspace. There were significant associations of age group, IRSED, physical functional limitation, BMI, with change in the amount of walking and MVPA. Significant associations were also found between gender and change in the amount of walking and sitting. Educational attainment was significantly associated with a change in sitting time. There were no significant associations between greenspace and changes in MVPA, walking and sitting.

Baseline correlates of the outcomes

Table 2 presents the outcome variables at baseline by T2D group. The amount of time spent on MVPA at baseline was significantly higher among the ‘No T2D’ group. There were no significant differences in the amount of time spent on walking and sitting between New T2D and No T2D.

Table 2

Outcome variables at baseline by type 2 diabetes status

Although the interactions between access to greenspace for each buffer size and status of T2D was not statistically significant for each outcome variable except for the changes in MVPA with percentage of greenspace within 2 km (p=0.039), the differences in trends between status of T2D were apparent as shown in figure 4.

Figure 4

Change (with 95% CI) in outcomes by proportion of greenspace (Bonferroni method was applied for multiple comparison). T2D, type 2 diabetes.

Greenspace and outcomes by diagnosis of T2D

Figure 4 presents marginal mean changes in the amount of walking, MVPA and sitting, and associated 95% CI by proportion of greenspace. A change in the outcome variable of greater than zero indicates an increase in that outcome at the follow-up study relative to the baseline study. Regardless of diabetes status and buffer size, there were no associations between percentage of greenspace and changes in amount of walking and sitting. For example, the 95% CI of changes in the amount of walking were overlapping between each category of greenspace regardless of buffer size. Although there were no significant changes in amount of walking with the percentage of greenspace, increasing trends were apparent among New T2D which peaked at >15%–20% of greenspace, whereas fairly stable trends were found among No T2D. Similar trends were also found for changes in the amount of MVPA.

Among New T2D, there was no significant association between the percentage of greenspace within 2 km buffer and changes in amount of MVPA. However, increasing trend was apparent with the peak at >15%–20% of greenspace. Among No T2D, the changes in amount of MVPA remained fairly stable with increasing percentage of greenspace (figure 4).

For changes in sitting time, there were no significant associations with percentage of greenspace regardless of buffer size. Among New T2D, the changes in amount of sitting decreased at percentage of greenspace >10%. Among No T2D, the changes in amount of sitting significantly decreased at follow-up and remained stable with increasing proportion of greenspace.

Discussion

This is the first study to explore environmental influences on the behaviours of people who transition into living with T2D. Overall, we found that there was a lack of association between access to greenspace at baseline and change in walking, MVPA and sitting time. We found no statistically significant interactions between access to greenspace and status of T2D for each outcome variable, except for the changes in MVPA with percentage of greenspace within 2 km. Although no significant interactions were found, possibly due to the small sample size of those with newly diagnosed T2D, the magnitude of changes in walking and MVPA increased as percentage of greenspace increased among New T2D while remain fairly stable among No T2D. There was no significant association between greenspace and sitting time with fairly stable trends among both New T2D and No T2D.

Among participants with newly diagnosed T2D, there were gradual increases in walking and MVPA with increasing proportion of greenspace within 1 km and 2 km buffers. However, these increases in walking and MVPA were no longer evident with >20% greenspace. This may be because around half of the participants with more than 20% of greenspace within a 2 km buffer (around 3% of the total sample) live near larger greenspace (area >1 km2). These large greenspaces are mainly national parks and nature reserve that may have limited public access points. These areas are often located in suburbs on the outskirts of the city with minimal pedestrian or other infrastructure to facilitate the regular use of greenspace for physical activity.47 Francis et al suggested that the type and functionality of the greenspace may be a salient factor in addition to quantity.48

Furthermore, the lack of association found between greenspace and walking and MVPA may be due to the increased participation in fitness activities taking place outside of neighbourhood greenspace. Such fitness activities include aerobics, gym activities, Pilates, weight training and yoga.49 In Australia, fitness centre/gym activities is the second most popular physical recreational activity after walking.50 Similarly, a Dutch study15 found no significant association between the amount of greenspace within 1 km radius of respondents’ home and meeting the Dutch public health recommendation for physical activity possibly due to a high density of fitness centres and so that access to greenspace is not a necessary condition for being physically active.15

The weak associations between sitting and proportion of greenspace may be due to the lack of detailed information on the setting and domains of sitting (home, car, work or recreation environment). In the 45 and Up Study, only total sitting time was measured at both baseline and follow-up. Self-reported total sitting time is subject to substantial measurement errors and does not distinguish occupational and transportation sitting from recreational sitting. Previous studies have found that correlates of sitting differed considerably by domain of sitting.51 Wallmann-Sperlich et al found a weak association between sitting duration and access to parks and recreation facilities52 and suggest that research investigating association between sitting time and environment should consider the diverse domains of sitting.52

Overall, the association between proportion of greenspace and change in physical activity appeared more prominent in New T2D than No T2D. These findings suggest that greenspace may have more motivating effect on physical activity among those newly diagnosed with T2D. Diabetes Australia recommends people with T2D start with at least 30 min of moderate physical activity every day or between 60 and 90 min every day if they are trying to lose weight.53 However, it appears that proximity to greenspace alone may not be sufficient to meet Diabetes Australia recommendations for those with newly diagnosed T2D.

The strengths of this study include a prospective design and a large population-based cohort study. Although diagnostic or clinical information was not available to confirm the diagnosis of T2D among participants, in this sample self-reported diagnosis of T2D has high sensitivity and specificity compared with hospital administrative data collections.31 Having outcome measures at two time points only over 2–5 years has limited our ability to track changes in lifestyle behaviours over longer periods of time.

A few additional limitations apply. We were not able to differentiate between different domains of MVPA and sitting, such as recreational, transport or occupational physical activity and sitting. We also don’t know whether each activity took place within the local greenspace. Further, greenspace included state forests and national parks which may or may not be conducive to walking and MVPA as urban parks and trails. We also could not categorise greenspace into more usable categories, for example, sports fields, bushland, presence of picnic facilities and so on, nor do we have access to the quality of the greenspace. Moreover, although we adjusted for a number of important potential confounders, there may yet be some residual confounding. However, we share this limitation with most other published studies on neighbourhoods and health.

Conclusion

This study indicates that neighbourhood greenspace is related to active lifestyles only to a very limited extent among people with newly diagnosed T2D. This is particularly so when there is moderate amount of greenspace (15%–20% of the neighbourhood). Future studies should consider including more comprehensive environmental measures about greenspace and other environmental attributes (eg, recreational facilities), more specific measures of physical activity and sedentary behaviour, such as the domain and location of each activity, and the more follow-up measures over longer period of time.

Acknowledgments

This research was completed using data collected through the 45 and Up Study (www.saxinstitute.org.au). The 45 and Up Study is managed by the Sax Institute in collaboration with major partner Cancer Council NSW; and partners: the National Heart Foundation of Australia (NSW Division); NSW Ministry of Health; NSW Government Family & Community Services—Carers, Ageing and Disability Inclusion; and the Australian Red Cross Blood Service. We thank the many thousands of people participating in the 45 and Up Study.

References

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Footnotes

  • Contributors SC participated in the design of the study, carried out the statistical analyses and drafted the manuscript. SM participated in the design of the study, helped draft the manuscript, helped with the interpretation and revised the manuscript. DD helped draft the manuscript, helped with the interpretation of the data and revised the manuscript. GM, EJC and AB helped with the interpretation of the data and revised the manuscript. BJ supervised the study, helped draft the manuscript, helped with the interpretation of the data and revised the manuscript.

  • Funding The research was funded from a NH&MRC Preventative Healthcare and Strengthening Australia’s Social and Economic Fabric Program Grant.

  • Map disclaimer The depiction of boundaries on this map does not imply the expression of any opinion whatsoever on the part of BMJ (or any member of its group) concerning the legal status of any country, territory, jurisdiction or area or of its authorities. This map is provided without any warranty of any kind, either express or implied.

  • Competing interests None declared.

  • Patient consent for publication In the 45 and Up Study, participants completed a baseline questionnaire and have provided informed consent for long-term follow-up and for the use of their data for research purposes.

  • Ethics approval The baseline 45 and Up Study and the SEEF Study were approved by the University of New South Wales Human Research Ethics Committee and the University of Sydney Human Research Ethics Committee, respectively.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data may be obtained from a third party and are not publicly available.

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