In our study, we found that both higher levels of physical activity (PA) and higher relative intensity of PA were associated with lower mortality. This inverse trend was apparent after adjusting for a wide range of confounders. Ill health, discomfort, fear of adverse effects, and well-meaning efforts of others to protect older persons from potential harm all potentially contribute to activity limitations. Since ill health may also be a consequence of low physical activity we included variables in a third model, which we conjectured to be possible consequences of physical activity such as hip fracture, falls, and history of heart attack. After adjustment for potential confounders as well as possible causal pathways variables (comorbidities) a significant trend of lower mortality with increased levels of duration and intensity of PA persisted.
Observational studies in the general adult population which included people aged 75 years and over have found a reduced risk of mortality with increased physical activity in both older women and men [9
]. The evidence has been inconsistent as to the levels of physical activity required to maximize health benefit. A recent systematic review of the benefits of moderate activity found a 19% reduction in mortality risk with 2.5 hours per week compared to no activity. The additional survival benefit from 7 hours activity per week was fairly small (24%) [15
]. Interestingly the benefit was somewhat stronger in the older age group (65 years and over) compared to the younger age groups. Other studies have been conducted specifically in the older age group [23
]. It is problematic to make a direct comparison between these studies and ours due to different methods of assessment and categorization of physical activity, different length of followup,and lack of stratified analysis by age 75 years and over. The UK Nottingham Longitudinal Study on Activity and Ageing measured customary physical activity (type, frequency, and duration) in people aged 65 years and over categorized as low, intermediate, and high [23
]. Relative to the high group, an increased 47% 12 year mortality risk was observed in men for the “intermediate" group and a 75% increased mortality for the “low” group. The increased risk was observed only for the low-activity group for women. A prospective study conducted in the US of community dwelling people aged 65 years and over found that walking more than 4 hours/week was associated with a 27% reduced risk of death [27
]. However, this association was substantially diminished by adjustment for cardiovascular risk factors and measures of general health status. Other studies in older people have reported improved survival from any level of physical activity compared to none [24
], or a mortality benefit from 3 or more hours per week of activity of at least moderate-intensity compared to none, even among frail people [26
] and a lower mortality rate over 10 months among frail people who did at least 2 hours activity a week [28
]. A US-based study of people aged 65 years and over found those who walked more than 4 hours per week had a lower mortality although this was significant only among persons aged 75 years and older [27
]. Bembom et al. concluded that the benefits of at least 22.5 metabolic equivalents (MET) hours per week could be greater for people aged 75 and over than for aged 54–74 years, but they had little detail on physical activity [25
We had no information on previous leisure activities in our study. Other studies have shown that the greatest declines in physical activity over time are associated with the highest mortality rates in men but not in women [29
], but that increasing leisure time activities even in later life is beneficial [30
]. The levels of habitual physical activity (of moderate or high intensity) in our study based on a community sample of people aged 75–84 years are reasonably high for this age group with half of participants achieving the current recommendation of at least 5 × 30 minutes of moderate physical activity per week. The Health Survey for England (HSE) reported that 72% of men and 82% of women aged 75 and over do not achieve at least 30 minutes per day on one- to four- days a week of at least moderate intensity [32
]. Direct comparison between our study and the Health Survey for England is not possible, because we did not measure frequency. The closest comparison is that 42% of participants in our study managed less than 120 minutes of at least moderate physical activity per week. This difference may be partly accounted for by the fact that the HSE categorized heavy housework and outdoor maintenance/DYI as moderate activity for the survey population of all ages. Our judgment was that for people aged 75 years and over, intensity of heavy housework as defined in our study (e.g., scrubbing floors on knees, moving furniture, spring cleaning, and polishing brass) and outdoor maintenance/DIY (e.g., washing, polishing and repairing the car, carpentry, erecting a fence or shed, brick/concrete laying, moving heavy loads,etc.) requires energy expenditure justifying inclusion in the heavy-intensity of PA category. Other studies in Europe which have included either domestic and DIY activities [33
] or leisure time activities [14
] have reported higher levels of PA in older people with up to two thirds of participants reporting moderate or high levels of physical activities.
Data on PA in our study covered a large range of typical activities in older people and took account of widely varying intensities and frequencies. Low level everyday mobility activities as well as shorter bouts of activities (e.g., time spent on feet in shops and stair climbing) were recorded. These are not usually counted in other studies such as the HSE even though some activities, such as hoovering, are included in the UK Department of Health recommendations. It is controversial whether domestic activity has health benefits [33
]. Domestic activity and shopping were included in a category of “consumptive” activity that did not predict mortality among people aged 70 and over during a 10–13 year follow-up after the analyses were adjusted for demographic factors, education, comorbidity, and physical and cognitive functioning [34
]. On the other hand, in a wider agegroup there was some indication of reduction in all-cause mortality for men and women over an average follow-up of 8 years [35
]. Some authors have suggested that psychosocial pathways, such as stress, may limit the benefits of domestic work [34
], at least for some groups [36
]. It is possible that our study participants were more health conscious and active than in the HSE survey. This could further explain the overall higher levels of PA achieved by our study subjects. In view of this, the intensity variable may be considered a better measure of PA performed. We categorized people in the high-intensity group on the basis of performing any high-intensity activity. We found no difference in models that excluded or included people with less than an hour's heavy activity a week.
We used questions adapted from the Allied Dunbar National Fitness Survey. We could not identify any validation studies conducted on the survey instrument. Discriminant validity was suggested in our study by the predictive association with thirds of physical activity and health status. Similar to other studies which used questionnaire methods to assess physical activity, we cannot exclude errors in the reporting of physical activity, for example, due to recall problems, over reporting due to perceived social desirability and the collection of data at a single point in time. However, results of assessment by a seven-day physical activity recall interview administered in a community health survey, a randomized clinical trial, and two worksite health promotion programmes suggest that physical activity recall provides useful estimates of habitual physical activity for research in epidemiological and health education studies [37
]. Moreover, self-report has some advantages over objective measures in that the latter often have to exclude those in the worst physical state [26
Undertaking physical activity is a complex behavior. Descriptive variables may be meaningfully partitioned into various categories as long as they are mutually exclusive of each other [38
]. In preparation for constructing new summary measures of PA from the questionnaire we conducted a structured review of the literature specific to the question of categorizing self-reported physical activity into relevant derived physical activity variables in older people. This work was further supported by conducting an overview of the exercise physiology of old age. The most frequent categorization of PA found was by total quantity (in minutes per week) and by intensity, frequency, and type of PA (e.g., walking). From the point of view of the older person the most problematic measurement is the intensity of activity undertaken. The frequently used classification of physical activity by rate of energy expenditure using energy expenditure values in METs based on young adults can be misleading due to the bigger effort, and thus higher energy expenditure, required in older age to accomplish given tasks. We have, therefore, taken the approach used mainly in Scandinavian studies where physical activity is graded in levels using a modified version of the scale developed by Grimby [14
]. We categorized participants into categories of “inactive” (engage in no or very few activities of only light intensity of not more than 30 minutes/week), “lightly active” (engage in light- and moderate-intensity activities up to one hour/week), “moderately active” (engage in light and moderate intensity activities up to 2.5 hours/week), “active” (engage in moderate physical activities for more than 2.5 hours/week and including at least 30 minutes of heavy intensity activity or active exercise/week) and “highly active” (engage in moderate physical activity for more than 4 hours/week or heavy intensity activity or exercise for over 2 hours/week). However, given the relatively high volume of physical activity performed by participants in our study and reduction in our original sample size due to incomplete data on confounders and co-morbidities, we categorized physical activity into tertiles by total amount of PA and three mutually exclusive categories of intensity (low, medium, and high) described in detail in the methods section.
There are a number of limitations in our study. Although we took account of a large number of potential confounders there may be other unmeasured confounders which could have attenuated our results. People with higher levels and intensity of physical activity had fewer health problems than those with the lowest levels. In common with other observational studies of physical activity in older people, it is difficult to establish whether poor health is a consequence of low physical activity or whether low physical activity is a consequence of poor health. Since poor health is associated with mortality, we controlled for this by including the major health conditions in our models. Although we did not have information on the severity of some conditions such as emphysema or angina, we included a measure of functional limitation (ADL) as a proxy indicator of poor health. We did not have any objective measures of physical activity. Using data from the US NHANES survey, Troiano et al. found differences in levels of physical activity based on self-report compared with accelerometers suggesting over estimation by study participants [41
]. However, as noted by the authors, accelerometry may underestimate physical activity because it does not take account of activities such as bicycling, swimming, and upper body activities.
Our results do not apply to people in long-stay hospital or nursing homes (an exclusion criterion for the trial) in whom physical activity levels are likely to be substantially different from the community sample. The response rate in our study was 71% and nonresponders were more likely to be women and current smokers. However, there were no other major differences in health measures between responders and nonresponders, and the mortality rates were similar. The 35% of responders who did not have full data on possible confounders were similar to those with full data. Moreover, the Model 1 and 2 mortality estimates for those with incomplete data were essentially the same as those with complete data.
Our results for people aged 75 to 84 years support the existing evidence that physical activity is beneficial and is associated with improved survival in those aged 75 years and over. Regular physical activity and/or exercise enable older people to retain higher levels of functional capacity (notably cardiovascular and neuromuscular function) and possibly slow the age-related decline in cognitive function. The benefits of increased levels of exercise in relation to mortality found by us and in previous studies apply to a range of daily activities and are by no means specific to structured exercise. Our study also shows that doing more strenuous physical activity (as well as light and moderate) has benefits in terms of survival. Significant natural reduction in muscle mass and consequent loss of strength is a natural irreversible process. However, considerable strength improvement of existing muscle mass with vigorous training is possible into the ninth decade of age [42
]. Since muscle strength is crucial to mobility, performing heavy physical activity will also undoubtedly lead to increased self-sufficiency in older age and there is a case for making resistance training a core component of disability postponing programmes for the elderly.
Although we were not able to report on the frequency of exercise below the weekly time unit and cannot, therefore, say with certainty how many times per week physical activity should be performed, the nature of our observations about daily customary activities suggests that activity took place on most, if not all, days. If customary physical activity such as housework, gardening, shopping, and walking is the main or sole component of physical activity for older people, it should be emphasized that increased activity (above the current recommended level) has considerable longevity benefit. While recommendations for older people appropriately focus on the provision and promotion of physical activity classes [6
], this should be integrated with an approach which additionally emphasizes home-based activities.