Cohort Profile: Updating the cohort profile for the MRC National Survey of Health and Development: a new clinic-based data collection for ageing research

Abstract

In a previously published cohort profile,1 we showed how the MRC National Survey of Health and Development (NSHD), the oldest of the British birth cohort studies, has played an important role in identifying the early origins of adult health and function. The study has a wealth of existing prospective data from birth; and with study members now in their early sixties and approaching conventional retirement age, the NSHD offers the opportunity to investigate how lifetime experience and exposures affect the chance of healthy ageing and reduction of functional decline and chronic disease in later life. Ageing populations, and the heterogeneity observed among ageing individuals, pose a grand challenge to society. We need to understand better how factors acting across the whole of life can affect the chance of living a long, healthy and independent life.2,3 The NSHD, one of the UK’s rich set of longitudinal cohort resources, facilitates a life course approach to the study of ageing, a strategic priority of the Medical Research Council4 and the other UK research councils and funders.5–7 Evidence is accumulating from the NSHD and from other cohort studies with information from birth, infancy or childhood that adult function and age-related chronic disease have their origins in early life experience and environment and share common risk factors operating across the life course.8–13 There is a growing consensus that biological ageing (a progressive, generalized impairment of function resulting in a loss of adaptive response to life challenges) is caused by the rate of accumulation of molecular and cellular damage from the beginning of life.14 Modifiable factors (such as nutrition and physical activity) and non-modifiable or random factors acting across the life course can alter exposure to sources of damage, and the effectiveness of body systems for maintenance and repair. The MRC Unit for Lifelong Health and Ageing (LHA) was established in 2008 to maximize the scientific potential of the NSHD and develop it into an interdisciplinary study of ageing. The LHA research team and their scientific collaborators secured MRC funding to invite study members to take part in their first adult clinic-based data collection to obtain new ageing outcomes, as well as repeat measures of health, function and life circumstances, previously collected by research nurses at home visits. Collection of data took place in 2006–07 in a feasibility study on 10% of the NSHD sample living near the Wellcome Trust Clinical Research Facility (CRF) Manchester, and since 2008 has been taking place on the remainder of the sample at five other UK CRFs (due for completion March 2011). The ageing outcomes in the latest NSHD follow-up were chosen to facilitate the testing of life course hypotheses that capitalized on the existing study data, and because they represented important public health problems or intermediate markers of such problems thought to be potentially modifiable. Quantitative ageing traits were preferred over binary outcomes as they provide greater power for analysis, which is important given that the sample contains less than 3500 study members still alive and living in Britain. The choice of outcomes also took into consideration whether the measures would be sufficiently attractive to induce study members in their early sixties to travel a considerable distance for a clinical assessment. For this data collection between ages 60 and 64 years, we chose to focus on physical and cognitive capability, the capacity to undertake the physical and mental tasks of daily living, as measured by physical performance tests (such as grip strength, chair rises, standing balance) and cognitive performance tests (such as verbal memory and information processing). These tests reflect underlying ageing processes rather than specific diseases per se; are the foundation for continued independence and quality of life, as we grow older; and predict future risk of disability, disease, morbidity and mortality.15–18 We also chose to study the structure and function of musculoskeletal and cardiovascular (CV) body systems because age-related changes in these systems threaten capability and account for a major proportion of the disease burden in the ageing population and because there may be opportunities to delay, if not reverse, adverse biological changes. We hypothesize that together these ageing outcomes co-vary in ways that have important practical implications for daily living, and for understanding the ageing process, the development of frailty, disease and longevity. The existing life course prospective data make this cohort particularly suited to test several hypotheses, namely: (i) early as well as adult life exposures and risks impact on these aspects of ageing; and (ii) exposure to earlier sources of risk (from gestation to early adulthood) adds substantially to, or is dependent on, the burden of mid-life risk. Our conceptual framework is that NSHD data