Physical and cognitive capability
Aims to identify the factors across life that influence how physical and cognitive capability change as we grow older.
Dr Hardy and Dr Cooper introduce
Physical and Cognitive Capability (Part One)
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Prof Ian Deary and Dr Marcus Richards introduce
Physical and Cognitive Capability (Part Two).
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What are physical and cognitive capability?
Physical capability refers to an individual’s capacity to undertake physical tasks needed for daily living. Cognitive capability refers to an individual’s capacity to undertake mental tasks needed for daily living.
Why study physical and cognitive capability?
Maintaining and even enhancing physical and cognitive capability as we grow older is important for healthy ageing, enabling people to live independently for longer and with a higher quality of life. Low levels or loss of capability are a threat to independent living, impact negatively on quality of life and are linked to risk of disease and death. Changes in physical and cognitive capabilities over time are useful indicators of the ageing process.
How are these capabilities tested?
Tests of physical capability include grip strength, standing balance, chair rises and walking speed. From the results of these tests we can study the full spectrum of capabilities, from low to high functioning.
A range of tests are used to measure cognitive capability. These tests assess memory, reasoning, speed of thinking and attention, and verbal and numerical skills. Sometimes specific tests are used to assess just one of these skills, and sometimes more general tests are used.
What we know and what we don’t know
Physical capability, and the body systems on which it depends, displays rapid growth in the first stages of life to reach a peak or plateau in early adult life, then declines with age in most people. This is also true for cognitive capabilities such as memory, reasoning, information processing speed and executive functions (responsible for processes like planning and multi-tasking).
Another kind of cognitive capability is based on knowledge ‘reserves’ that individuals accumulate over their lifetime. This can be assessed by studying, for example, people’s vocabulary. For most people this reserve is stable in later life and there is some evidence that it can influence the rate of decline in cognitive skills with age.
Genetic factors explain some of the variation in physical and cognitive capability. Environmental factors across life are also associated with the development and decline in capability.
What we did not know is whether the same links between lifetime factors and capability are found across different groups of people and at different ages.
What we are researching
We first examined whether there was consistent evidence that the objective measures of physical capability to be used across HALCyon were useful markers of ageing.
We then investigated the best ways to harmonise the measures of capability available in each of the HALCyon cohorts so that they could then be studied across cohorts in a comparable way.
Once the data were harmonised we explored age, gender and cohort differences in capability and examined whether declines in physical and cognitive capability were interlinked.
We have also examined lifetime predictors of cognitive and physical capability across cohorts, complemented where appropriate with in depth studies in individual cohorts, including:
- Lifetime socioeconomic position
- Birth weight, childhood growth and adult body size
- Childhood mental abilities
- Lifetime health status and lifestyles such as physical activity
We have also investigated whether physical or cognitive capability are linked with subsequent wellbeing (see also WP2).
Investigators working on this WP have also contributed to projects being undertaken across all the other WPs which have used measures of physical and cognitive capability as outcome variables. Results for these projects are summarised in the other WP pages.
What have we found so far?
Physical and cognitive capability
- In a systematic review and meta-analysis of all published data we showed that, after adjusting for age, those who have weaker grip strength, slower walking speed, greater difficulty getting up from a chair and poorer standing balance performance are more likely to die sooner and develop health problems than people who perform well in these tests. (Cooper et al., British Medical Journal 2010 and Cooper et al., Age and Ageing 2011). The BMJ paper received wide news coverage and was reported in national newspapers, including the Independent, Guardian and Daily Mail, radio news reports and internationally on internet news sites.
- We found that in UK populations, as in populations from other countries, physical capability levels decrease with age and that men have higher physical capability levels than women from mid-life onwards. However, the gender difference in grip strength got smaller with increasing age and the gender difference in walking speed was fully explained by differences in height (Cooper et al., PLoS ONE 2011).
- In a meta-analysis including all previously published studies, the HALCyon cohorts and other unpublished data we found evidence of modest associations between childhood socioeconomic circumstances and physical capability in adulthood; those people with lower childhood socioeconomic position had lower levels of physical capability later in life than people with higher childhood socioeconomic position (Birnie, Cooper et al., PLoS One 2011). The mean difference observed across the studies translates into an 11% increase in mortality for those most versus least deprived. Impact on quality of life may be greater.
- In an in depth study using data from the NSHD, we explored the relationship between lifetime socioeconomic position and physical capability further and showed that the associations between childhood socioeconomic position and physical capability in midlife were partially explained by growth, development and the home environment in childhood (Strand et al., European Journal of Epidemiology 2011).
- In another in depth study in the NSHD, a large increase in reports of functional limitations between 43 and 53 years was revealed as were growing socioeconomic and gender inequalities. These findings provide the first evidence that prevention of disability in old age should begin early in midlife, especially for women from manual occupation households (Murray et al., Journal of Gerontology: Medical Sciences 2011).
- In the NSHD we also showed evidence of cumulative benefits of physical activity across adulthood on physical performance in later life. We found no evidence of an association between lifetime physical activity and grip strength (Cooper et al., American Journal of Preventive Medicine 2011).
- In a systematic review and meta-analysis of all published studies we found consistent evidence of a positive association between birth weight and muscle strength which is maintained across the life course (Dodds et al., Journal of Nutrition, Health and Aging 2012).
- In a meta-analysis of eight of the HALCyon cohorts we found that higher body mass index in adulthood was consistently associated with slower chair rise and walking speeds and poorer standing balance performance. Low grip strength was also associated with poor physical performance. There was evidence of additive effects of BMI and grip strength; those with the lowest grip strength and highest BMI had the worst performance (Hardy et al., PloS One 2013)
- In the five HALCyon cohorts with data on physical capability and positive mental wellbeing (assessed using the Warwick-Edinburgh Mental Wellbeing Scale) we found evidence that higher levels of physical capability were associated with higher levels of positive mental wellbeing assessed five to ten years later. However, these effects were modest (Cooper et al., Age 2013).
- In the NSHD we showed that higher neuroticism in adolescence and slightly poorer scores on tests of cognitive function in midlife appeared to be dependent on cognitive ability in childhood (Gale et al., Journal of Gerontology: Psychological Science 2010).
- We reported that cognitive ability in earlier life appears to be protective against later cognitive declines in NSHD, although this may not happen across all stages of the ageing process or across all samples as this finding was not replicated in the older Lothian cohort (Gow et al., Intelligence 2012).
- In ELSA, we found that there was no evidence that being more depressed led to an acceleration in cognitive decline and no support for the hypothesis that there might be reciprocal dynamic influences between cognitive ability and depressive symptoms (Gale et al., Psychological Medicine 2012).
- In three birth cohorts we found consistent evidence of an association between achieving a university education and higher fluid cognition in later adulthood (Clouston et al., International Journal of Epidemiology 2012).
- In a HALCyon and IALSA systematic review which aimed to identify all studies of the longitudinal association between cognitive and physical capability published since 2000, only 7 studies were found that had examined the link between changes in fluid cognition and changes in physical capability. Overall, findings were not sufficiently strong or consistent to support evidence of a common process of decline (Clouston et al., Epidemiologic Reviews 2013).
Please see the Case for Support for a detailed, more technical overview of the work packages.
Kuh D, Cooper R, Hardy R, Richards m, Ben-Shlomo Y (Eds). A life course approach to healthy ageing. Oxford University Press to be published January 9th 2014.
- Chapter 2: A life course approach to physical capability
Dr Rachel Cooper, Professor Rebecca Hardy, Professor Avan Aihie Sayer, Professor Diana Kuh
- Chapter 3: A life course approach to cognitive capability
Professor Marcus Richards and Professor Ian J Deary