Urban residential environments and senior citizens' longevity in megacity areas: the importance of walkable green spaces. .

Study objectives: To study the association between greenery filled public areas that are nearby a residence and easy to walk in and the longevity of senior citizens in a densely populated, developed megacity.

Design: Cohort study.

Methods: The authors analysed the five year survival of 3144 people born in 1903, 1908, 1913, or 1918 who consented to a follow up survey from the records of registered Tokyo citizens in relation to baseline residential environment characteristics in 1992.

Main results: The survival of 2211 and the death of 897 (98.9% follow up) were confirmed. The probability of five year survival of the senior citizens studied increased in accordance with the space for taking a stroll near the residence (p<0.01), parks and tree lined streets near the residence (p<0.05), and their preference to continue to live in their current community (p<0.01). The principal component analysis from the baseline residential environment characteristics identified two environment related factors: the factor of walkable green streets and spaces near the residence and the factor of a positive attitude to a person's own community. After controlling the effects of the residents' age, sex, marital status, and socioeconomic status, the factor of walkable green streets and spaces near the residence showed significant predictive value for the survival of the urban senior citizens over the following five years (p<0.01).

Conclusions: Living in areas with walkable green spaces positively influenced the longevity of urban senior citizens independent of their age, sex, marital status, baseline functional status, and socioeconomic status. Greenery filled public areas that are nearby and easy to walk in should be further emphasised in urban planning for the development and re-development of densely populated areas in a megacity. Close collaboration should be undertaken among the health, construction, civil engineering, planning, and other concerned sectors in the context of the healthy urban policy, so as to promote the health of senior citizens.

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It is generally recognised that greenery filled public areas provide comfortable and pleasant living environments for urban residents. (1,2) Comfortableness, feeling comfortable, in relation to physical environments in densely populated areas has been studied by measuring people's preferences. (3) However, there is a controversy as to whether substantial positive health outcomes result from living in localities with greenery filled public areas. (4) Hence, the tendency has been to regard the provision of greenery filled public areas merely as a matter of preference.

For convenience, this paper will refer to greenery filled public areas that are nearby and easy to walk in such as parks and tree lined streets as "walkable green spaces".

The health influences of residential environments have not been investigated adequately. (5) It generally has been acknowledged that it is difficult to demonstrate an association between health outcomes and residential environments because the health consequences often are not apparent until some years have passed, and because many other health determinants also affect both the environmental conditions of residential areas and the health status of residents. However, there is a growing concern for physical environmental factors in facilitating or modifying different health behaviours conducive to health. (6) Thus, we conducted a longitudinal cohort study to obtain evidence showing the health consequences of living in a residence that has walkable green spaces nearby.

It has been reported that in an urban society a wide variety of physical, social, and economic factors exhibit interrelationships while also affecting the health of residents. (7-10) Therefore, in this cohort study, we considered multiple variables concerning physical, social, and economic environments, and we analysed independent effect of walkable green spaces on the longevity of senior citizens.

Health promotion of older people in a megacity has become a prime concern in an aging society. (11-13) It is well known that a sedentary lifestyle is a key risk of premature morbidity and mortality. (14) For older adults, a sedentary lifestyle is a greater risk of reducing their physical function than that for younger adults. (15) Therefore, to facilitate healthy aging, physically active living should be encouraged by deliberate arrangements. Giving an exercise prescription was reported as an effective intervention for sedentary patients to facilitate their physically active living. (16,17) To approach a healthy population in general before they become sedentary patients, we considered there are some appropriate physical environment conditions conducive to their physically active living and longevity. We were particularly interested to study whether walkable green spaces provide a supportive environment that promotes the health of senior citizens in densely populated urban areas.

Collaboration of the health and urban planning sectors would be more firmly grounded if there were evidence of the health promoting outcomes of particular environments that can be realised through urban planning. People's preferences regarding a comfortable living environment are subjective and often are based on intangible factors. In contrast, longevity is an objective measure that can be directly quantified. Health issues can provide strong, logical factors to be considered in urban planning decision making. Demonstrable evidence that living in an area that has walkable green spaces has a positive impact on longevity would constitute key evidence for policy making and could facilitate intersectoral collaboration regarding health promoting urban planning.

Thus, the objective of this study was to investigate, through a cohort study of older people, the association between walkable green spaces near the residence and the longevity of senior citizens in a densely populated, developed megacity in order to provide facts for evidence based policy making and to advance intersectoral collaboration in urban planning so as to promote the health of senior citizens.

METHODS

Sampling

A representative sample of residents born in 1903, 1908, 1913, or 1918 was selected from resident registration records in two cities in the Tokyo metropolitan area--one in the east part and the other in the west part--in 1989. The following sampling rates were applied: 1/2 for people born in 1913 or 1918, and 1/1 for people born in 1903 or 1908. A total of 7362 people were selected and asked to participate in a mail follow up survey of their individual functional status and health. A total of 5924 people consented for this mail questionnaire follow up survey. In 1992, a subsequent questionnaire survey was conducted of those who agreed to participate. We asked about their residence's environmental conditions, and about their functional status, lifestyles, living arrangements, and socioeconomic status. A total of 3144 people …