Scottish Longitudinal Study
Development & Support Unit
Modelling Environmental Risk for Dementia in the Scottish Mental Survey 1947 sample
Luisa Parkinson, Alzheimers Scotland Dementia Research Centre (ASDRC), University of Edinburgh
Dr Tom Russ, ASDRC, University of Edinburgh
Prof Finn Lindgren, University of Edinburgh
15th February 2021
Using the Scottish Longitudinal Study sample of Scottish Mental Survey 1947 linked to health data to ascertain dementia outcomes, this study investigates the role of environmental factors in childhood and later life (over 55 years old) on the risk of developing dementia. The aims of the study will be to explore the following questions:
- Can environmental factors, such as air pollution and drinking water quality, explain some or all of the non-random geographical variation in dementia risk?
- Are the effects of environmental factors cumulative over a lifetime or does either early or late life exposures exert a greater effect?
Dementia is a life-course disease with the risk increasing with age, so increasing life expectancy and demographic shifts towards an ageing population, mean that the prevalence of dementia is predicted to increase to over 1 million people by 2025 and 2 million people by 2050 In the UK (Prince et al, 2013). As a result the current associated costs of around £17 billion are also predicted to rise.
Previous studies have shown a non-random geographic variation in the risk of developing dementia (Russ et al, 2012), which remains even after accounting for genetic variation (Gatz et al, 2006; Russ et al, 2015). There is growing evidence that some of this geographic variation in dementia risk may be explained by environmental factors, such as air pollution and the different solutes in drinking water (Killin et al, 2016; Marabotti et al, 2017, Russ et al, 2019). However, most of these studies are cross-sectional and use a snapshot of exposure to environmental factors, rather than trying to address the varying exposure over a life-course. Therefore, questions remain about whether there is a sensitive period to exposure, such as childhood, mid-life, or later life, or whether the effects are cumulative over a life-course.
The combination of both childhood and later life data provides a unique data set, in which to explore the life-course effects of environmental factors on the risk of developing dementia, whilst controlling for other factors that may influence that risk.
Deary, Ian J., Lawrence J. Whalley, and John M. Starr. 2009. “A lifetime of intelligence: Follow-up studies of the Scottish Mental Surveys of 1932 and 1947.” Washington: American Psychological Association.
Gatz, Margaret, Chandra A. Reynolds, Laura Fratiglioni, Boo Johansson, James A. Mortimer, Stig Berg, Amy Fiske, and Nancy L. Pedersen. 2006. “Role of Genes and Environments for Explaining Alzheimer Disease.” Arch. Gen. Psychiatry 63 (2): 168–74. https://doi.org/10.1001/archpsyc.63.2.168.
Huang, Zengyi, Zhiqiang Feng, Chris Dibben, Caroline Brett, and Ian Deary. 2017. “The Scottish Longitudinal Study 1936 Birth Cohort.” SLS-DSU Technical working paper 7. https://calls.ac.uk/wp-content/uploads/LSCS-WP-7_March2017.pdf
Killin, Lewis O. J., John M. Starr, Ivy J. Shiue, and Tom C. Russ. 2016. “Environmental Risk Factors for Dementia: A Systematic Review.” BMC Geriatr 16 (October). https://doi.org/10.1186/s12877-016-0342-y.
Marabotti, Claudio, Paolo Piaggi, Paolo Scarsi, Elio Venturini, Romina Cecchi, and Alessandro Pingitore. 2017. “Mortality for Chronic-Degenerative Diseases in Tuscany: Ecological Study Comparing Neighboring Areas with Substantial Diﬀerences in Environmental Pollution.” Int J Occup Med Environ Health 30 (4): 641–53. https://doi.org/10.13075/ijomeh.1896.00972.
Prince, M., M. Guerchet, and M. Prina. 2013. “The Global Impact of Dementia 2013-2050.” London: Alzheimer’s Disease International.
Russ, T. C., G. D. Batty, G. F. Hearnshaw, C. Fenton, and J. M. Starr. 2012. “Geographical Variation in Dementia: Systematic Review with Meta-Analysis.” International Journal of Epidemiology 41 (4): 1012–32. https://doi.org/10.1093/ije/dys103.
Russ, Tom C., Margaret Gatz, Nancy L. Pedersen, Jean Hannah, Grant Wyper, G. David Batty, Ian J. Deary, and John M. Starr. 2015. “Geographical Variation in Dementia: Examining the Role of Environmental Factors in Sweden and Scotland.” Epidemiology 26 (2): 263–70. https://doi.org/10.1097/EDE.0000000000000230.
Russ, Tom C., Lewis O. J. Killin, Jean Hannah, G. David Batty, Ian J. Deary, and John M. Starr. 2019. “Aluminium and fluoride in drinking water in relation to later dementia risk.” The British Journal of Psychiatry: 1-6. https://doi.org/10.1192/bjp2018.287.
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