ESRC/MRC interdisciplinary postdoctoral fellowship

Title: Lifecourse exposure to socioeconomic circumstances and physical function

Main discipline: Statistics, Methods and Computing

Secondary discipline: Medical Sciences

Applicant: Kate Birnie

Mentor: Professor David Gunnell

Physical function refers to an individual's ability to undertake physical tasks needed for daily living. Measures such as gait speed and balance tests are simple, objective measures of physical function that have also been shown to act as markers of current health and predict subsequent disability and death in older people. The ability to carry out physical performance tests involves muscle strength, agility, speed, balance control and cognitive understanding of what the test requires.

Physical capability, and the body systems on which it depends, shows rapid growth in early life to reach a peak or plateau in young adulthood and declines with age in most people. This research proposal is extends work from my PhD investigating diet and socioeconomic circumstances in childhood and physical function in old age, measured by walking speed and balance ability in the Boyd Orr and Caerphilly studies, supervised by Professors Yoav Ben-Shlomo and Richard Martin. We found, for example, that accumulating socioeconomic disadvantage from childhood to adulthood is associated with worse physical function in old age. Participants who moved from a low socioeconomic position in childhood to a high socioeconomic position in adulthood had walking times that were 3% (95% CI: -2%, 8%) slower than people who had a high socioeconomic position in both periods. Participants who moved from a high socioeconomic position in childhood to a low adulthood socioeconomic position had walking times that were 5% (95% CI: -2%, 12%) slower. People with low socioeconomic position in both childhood and adulthood had walking times that were 10% slower (95% CI: 5%, 16%; P for trend less than 0.001). Higher body mass index was associated with reduced ability to perform the flamingo balance test; a standard deviation increase in midlife body mass index and in old age body mass index was associated with a 4% slower walk time in old age.

To understand the dynamics of poor functioning in old age, we wish to study physical performance in childhood and consider its lifetime determinants; this may offer possibilities for intervention in earlier life to develop and maintain peak levels of performance or to slow its rate of decline with age. Early life factors may influence both the development of biological capital promoting physical capability, and, alongside adult factors, the timing and rate of decline.

There is evidence that early growth and development affect functional measures, such as muscle strength. A hormonal pathway such as variations in insulin / insulin-like growth factor (IGF) levels, could link growth and nutrition in early life with physical function. The IGF system includes two nutritionally-influenced peptides (IGF-I and -II), important regulators of fetal and post-natal growth, and their binding proteins (IGFBP 1 to 6). Both IGF-I and IGF-II increase muscle mass and strength and hence might influence measures of physical function. There is little previous research on this topic.

There is a strong inverse association between smoking behaviour and Parkinson's disease (PD) a neurodegenerative disorder of later life associated with dopamine deficiency. This finding is strong and consistent across different populations where the confounding structures would be expected to be different. It is also seen amongst young onset cases suggesting it cannot be due to selective mortality. Two possibilities remain (a) causal effect of nicotine or smoking products that are neuroprotective; (b) dopamine levels are also associated addictive prone behaviour so tht non-smoking is a crude proxy measure of a pre-clinical susuceptibility to later PD. We can examine whether subtle differences in motor behaviour prior to onset of smoking is associated with initiation and maintenence of smoking in adolesence. Our prior hypothesis is that non-smokers will perform worse after conditioning on other determinants of smoking behaviour.

Data from ALSPAC would be used investigate the following hypotheses; that poor balance/motor ability at ages 7-11 years is associated with:

1. Socioeconomic disadvantage

2. Poor diet and short stature (a marker of poor nutrition during the growing years) in childhood

3. Adiposity in childhood

4. Low IGF-I and IGF-II levels (controlling for IGFBP-2 and IGFBP-3)

5. Non-smokers will have worse pre-smoking motor function.

This work would form part of an ESRC/MRC postdoctoral fellowship to produce publications, disseminate research findings and carry out additional research linked to the PhD. Data from ALSPAC would greatly contribute to the evidence base of lifetime exposures on physical function.