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Thursday 10 September, Parallel session B
Methods
A novel approach to testing the lifecourse effect of body sizes on blood pressure in later life using partial least squares regression
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  1. Y-K. Tu1,2,
  2. A. Woolston1,
  3. P. Baxter1,
  4. M. S. Gilthorpe1
  1. 1
    Biostatistics Unit, Centre for Epidemiology and Biostatistics, University of Leeds, Leeds, UK
  2. 2
    Leeds Dental Institute, University of Leeds, Leeds, UK

    https://doi.org/10.1136/jech.2009.096719o

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      Introduction

      Recent studies claimed that postnatal catch-up growth might have a stronger impact on health in later life than birth size. As growth is a continuing process in lifecourse, the challenge is therefore to tease out the impact of body size in difference critical phases of lifecourse. One problem is that it is impossible to use ordinary least squares regression to differentiate the effects of birth sizes, growth and current body sizes, because growth is generally defined as the difference between birth and current size. The aim of this presentation is to propose a novel approach to testing lifecourse effects of body sizes on health outcomes using partial least squares (PLS).

      Materials and Methods

      Longitudinal data from a cohort of 960 males and 834 females recruited in Philippines during 1983–4 were used for statistical analysis. Body weight z-scores were used as the measure for body sizes, and the outcomes were systolic (SBP) and diastolic (DBP) blood pressure measured in 2002. PLS regression was used to test the impact of birth weight z-scores, change in body weight z-scores during different stages of growth, and current body weight z-scores on SBP and DBP.

      Results

      For SBP, birth size had a small negative association and the change in z-scores between age 1 and 2 had a stronger positive association than the change between birth and age 1. Growth after age 8 had a much stronger association than early growth, but current body size had the largest association. For DBP, birth size had a small positive association, and early growth had small associations in females. Growth after age 8 had a much stronger association than early growth, but current body size still had the largest positive association. In contrast, early growth had stronger associations with DBP in males, whilst current body size still had the largest association.

      Conclusion

      PLS regression estimates the associations between birth sizes, changes in body sizes at different phases of lifecourse and current body sizes simultaneously, and therefore misinterpretation such as reversal paradox can be avoided. Results from PLS analysis suggested that current body size had the largest positive association with SBP and DBP, whilst birth size had small negative or positive associations with blood pressure. Later growth in childhood and adolescence had stronger associations with SBP than early growth before age 2, but the associations between growth in body sizes and DBP were more complex.