Abstract
Objectives Associations of cognitive function assessed in adulthood with coronary heart disease (CHD) and stroke might reflect a causal effect or could be explained by residual confounding or a common underlying pathology (atherosclerosis) that links both declines in cognitive function and increased risk of cardiovascular disease (i.e. reverse causality). Our objective was to examine the association of childhood intelligence (assessed at an age when generalised atherosclerosis would be extremely unlikely) with risk of CHD and stroke in later life in a cohort of females and males on whom information on a wide range of potential confounding factors is available. Methods Cohort study of 11,125 individuals born in Aberdeen, Scotland, between 1950 and 1956, who had childhood intelligence measured at ages 7, 9, 11 and who have been followed up by linkage to hospital admissions and mortality data. Results The cohort contributed 264,672 person years of follow-up and over this time 93 females experienced CHD and 56 experienced a stroke; 264 males experienced CHD and 67 a stroke. There were inverse associations of childhood intelligence measured at all 3 ages (7, 9, 11 years) with both CHD and stroke, with some evidence that the association with intelligence assessed at age 11 was stronger than at younger ages. The magnitude of associations were similar for CHD and stroke. Adjustment for a range of potential confounding factors did not markedly attenuate the associations and there was evidence that the association was stronger in females than in males. For example, the age adjusted hazard ratio of a combined outcome of CHD and stroke per 1 standard deviation (SD; 1SD = 15 points) difference in intelligence score at age 11 in females was 0.52 (95% CI: 0.42, 0.64) and in males was 0.78 (95% CI: 0.68, 0.90), with adjustment for all potential confounding factors these became 0.60 (95% CI: 0.48, 0.76) and 0.84 (95% CI: 0.72, 0.98) respectively; P-value for interaction with gender in both models =0.002. Adjustment for educational attainment attenuated both associations to the null and removed evidence of a gender difference. Conclusions Our results suggest an association of intelligence in childhood with future CHD and stroke that is unlikely to be explained by reverse causality and was robust to adjustment for a wide range of confounding factors. This association appeared to be mediated by educational attainment. The gender difference seen in our study requires replication in other studies.
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Acknowledgements
We are very grateful to Raymond Illsley for providing us with the data from the Aberdeen Child Development Survey and for his advice about the study. Graeme Ford played a crucial role in identifying individual cohort members and in helping us initiate the process of revitalisation. Doris Campbell, George Davey Smith, Bianca de Stavola, Marion Hall, David Godden, Diana Kuh, Glyn Lewis, Susan MB Morton and Viveca Östberg collaborated with the authors to revitalise the cohort. Margaret Beveridge assisted Heather Clark in the study management. We would also like to thank staff at the ISD (Edinburgh), GRO (Scotland) and NHSCR (Southport) for their substantial contributions and John Lemon who undertook the linkage to the Aberdeen Maternity and Neonatal Databank. Finally, we thank the study participants.
Funding
The Aberdeen Children of the 1950s Study was funded as a component project (G0828205) of a Medical Research Council Co-operative Group Life-course and trans-generational influences on disease risk (G9819083). The Scottish Chief Scientist Office provided funds for a study of relationships of childhood intelligence. D. A. Lawlor is funded by a Department of Health (UK) Career Scientist Award and David Batty is a Wellcome Trust Fellow. The UK Medical Research Council (MRC) and the University of Bristol provide core funding for the MRC Centre for Causal Analyses in Translational Epidemiology. The UK MRC and University of Edinburgh provide core funding for the MRC Centre for Cognitive Ageing and Cognitive Epidemiology. The MRC Social and Public Health Sciences Unit receives funding from the UK Medical Research Council and the Chief Scientist Office at the Scottish Government Health Directorates. The views expressed in this paper are those of the authors and not necessarily any funding body. The authors had full access to data and the funding bodies did not influence the data collection, analysis or interpretation of results.
Ethics
The Scottish multi-centre research ethics committee and local research ethics committees plus the Scottish Privacy Advisory Committee approved the revitalisation of the Children of the 1950s cohort. All record linkage was undertaken by ISD, who provided us with an anonymised dataset for analysis.
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Lawlor, D.A., David Batty, G., Clark, H. et al. Association of childhood intelligence with risk of coronary heart disease and stroke: findings from the Aberdeen Children of the 1950s cohort study. Eur J Epidemiol 23, 695–706 (2008). https://doi.org/10.1007/s10654-008-9281-z
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DOI: https://doi.org/10.1007/s10654-008-9281-z