Abstract
The effects of interventions on multiple lifestyle and metabolic risk factors, initiated in midlife or later in a healthy population, on the long-term risk of first-ever stroke is not known. A particular methodological challenge in observational studies is to estimate the unbiased effect of a time-varying exposure in presence of time-varying confounders, if those confounders are affected by prior exposure. In such cases, the parametric g-formula can be applied to estimate an unbiased effect. We applied the parametric g-formula to estimate the 18-years (1994–2012) cumulative stroke risk under different scenarios of hypothetical interventions on levels of blood pressure, cholesterol, weight, physical activity, smoking and alcohol intake; and compared these to the observed scenario, to calculate the population risk ratios and risk differences. Among 14,796 eligible participants in the prospective, population-based Tromsø study (baseline mean age 46.1 years, 51% women), the observed 18-years stroke risk was 5.9%. A feasible joint hypothetical intervention on six lifestyle and metabolic risk factors would reduce the 18-year stroke risk by 32% (95% confidence interval 16, 44). A combination of more intensive interventions reduced the estimated 18-years stroke risk by 64% (95% confidence interval 40, 80). Blood pressure reduction and quitting smoking significantly reduced the risk when applied separately.
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Acknowledgements
We are grateful to Priyanka Jain, Stein Harald Johnsen, Inger Njølstad, Maja-Lisa Løchen for valuable contribution; and to all the participants in the Tromsø Study.
Funding
The Tromsø Study has been supported by the Research Council of Norway; the Norwegian Council on Cardiovascular Disease; the Northern Norway Regional Health Authority; the University of Tromsø; the Norwegian Foundation for Health and Rehabilitation; and the Odd Berg Research Foundation. AM. Vangen-Lønne receives a research grant from the Northern Norway Regional Health Authority.
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Vangen-Lønne, A.M., Ueda, P., Gulayin, P. et al. Hypothetical interventions to prevent stroke: an application of the parametric g-formula to a healthy middle-aged population. Eur J Epidemiol 33, 557–566 (2018). https://doi.org/10.1007/s10654-017-0344-x
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DOI: https://doi.org/10.1007/s10654-017-0344-x