The link between exercise, Alzheimer’s and mortality

Older people, exercise

A cohort study in Hong Kong, take a look at how physical activity can effect the development of Alzheimer’s disease, lung related illnesses and the risk of falls.

Physical activity (PA) is a very important and potentially modifiable factor of health – especially in modern living where one enjoys high level of automation. PA is likely to be equally important in older people who are more likely to have chronic diseases and disabilities. However, there is lack of information surrounding how PA interacts with physical fitness, the types and doses of PA, and the clinical outcomes on which PA has greater influence.

To address these questions, one needs to rely on data in prospective cohort studies. In Hong Kong, our research centre has been conducting the MrOS and MsOS Hong Kong cohort study which was originally designed to examine the risk factors of osteoporotic fractures in older people. Between 2001-2003, we recruited from the community 2000 men and 2000 women aged 65 to 82 years. Detailed information about their health and lifestyle was collected at baseline and mostly repeated at year two, four, seven and 14.

Physical activity and mortality

PA has been shown to be associated with lower mortality risk. But this may be confounded by cardiorespiratory fitness, as physically fit people are generally fitter than those who are sedentary. During year seven of the MrOS and MsOS cohort study, cardiorespiratory fitness was measured in a subgroup of subjects, and physical activity pattern was measured by the Physical Activity Scale for Elderly (PASE). When we looked at the mortality at 5.3 years after that follow-up, we found that higher level of self-reported PA was associated with reduced risks of all-cause mortality independent of cardiorespiratory fitness (p for trend=0.015).1 The implication is that PA would benefit older people with the whole spectrum of cardiorespiratory fitness.

Accelerometers-measured physical activity in older people

Research in PA has relied on self-reported questionnaires which have limited validity because of recall bias. This is especially pertinent in older people who are prone to have cognitive impairment. In recent years, there has been a move towards continuous monitoring of physical activity by wearable accelerometer. At our research centre, we have chosen to use the Actigraph GT3X accelerometer (Pensacola, FL, USA) worn over the wrist. The advantages are convenience of use and better acceptability by older subjects, which would hence improve wear compliance. At year 14 follow-up, wrist accelerometer data over seven days was available in 641 subjects.

PA and falls

We examined the association between PA as estimated by wrist accelerometers and incidence of falls in the year after the year 14 follow-up of MrOS and MsOS cohort study. Interestingly, we found that older people who were inactive or highly active had a two-fold increase in fall rate when compared with those who were moderately active. Upon separating the accumulative nature of PA, bouted PA (PA accumulated in episodes ≥10 minutes) have contributed to the significant finding. The effect of bouted PA on rate of falls were independent of other important fall-related risk factors (e.g., fall history, cognitive function). This indicates that the most active were as at risk as the inactive in fall risk among older people.

PA and cognitive impairment

Among those MrOS and MsOS study subjects who had wrist accelerometers data at year 14, 265 had normal cognitive function, 97 had mild cognitive impairment (MCI) and 21 had dementia according to Montreal Cognitive Assessment score and clinical examination. We combined this data with that of 217 subjects with early Alzheimer disease (AD) and 15 with MCI in another cohort study. When compared with subjects with normal cognition, the subjects with AD were less active and spent more time in sedentary behaviour. But MCI subjects were not different from normal subjects in any PA parameters.

The lack of association between MCI and PA may be due to the selection bias towards better cognitive function among those participating in follow-up. The subjects with later stages of MCI might have been under-represented in our sample. Further follow-up of the MrOS and MsOS study subjects may shed more light on the potential changes in PA in people with MCI.

PA and lung function

PA may be limited by impaired lung function which is common in older people. On the other hand, PA may help in preserving lung function with ageing. We examined the association between lung function and PA in 364 older subjects without chronic lung diseases, half of whom were participants of MrOS and MsOS cohort study. It was found that older men with better lung function had higher activity counts, spent more time in bouted activities (more than five minutes at a time) and spent less time in sedentary behaviour.

To our surprise, there was no significant association between PA and lung function for women. A possible explanation for this is that PA in older women are more related to daily chores that they are committed to do irrespective of their exercise tolerance. Observational studies aiming to examine the effect of PA on lung function should take this gender difference into account.

Future direction

PA will continue to be a major research focus for our centre. Our colleagues in Architecture has developed algorithms which can estimate the amount of green space and other environmental variables, based on home addresses and historical satellite data. By correlating these environmental variables and accelerometer data, one can gain more insight on how home environment may impact on the PA pattern of older people. The year 16 follow-up of the MrOS and MsOS cohort is due to start very soon. The prospective data particularly in accelerometers will inform on the factors of PA decline in the old-old.

When compared with wrist worn accelerometers, thigh worn accelerometer provides better quality data on PA, posture and sleep. Our centre has recently joined the Pro Pass research consortium which seeks to foster international collaborations in using thigh worn accelerometers to predict outcomes. Apart from the MrOS and MsOS cohort study, we plan to collect thigh worn accelerometer data in the young old and nursing home residents.

All in all, the technology of accelerometer offers exciting opportunities to examine the potential influences of PA on health outcomes in older people. Our centre would welcome international collaborations in this important area of gerontological research.

Please note, this article will appear in issue 32 of SciTech Europa Quarterly, which is available to read now.

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