School of Social and Community Medicine University of BRISTOL Longitudinal analysis of diet in ALSPAC Laura D Howe EUCCONET, Bristol, October 2011

School of Social and Community Medicine University of BRISTOL Outline  Trajectories of energy intake and macro- nutrients  Planned analysis  Very preliminary results

School of Social and Community Medicine University of BRISTOL

School of Social and Community Medicine University of BRISTOL

School of Social and Community Medicine University of BRISTOL Data issues  Different # measures per individual  Exact ages of measurement vary  FFQ and diary data  Want a full trajectory that is comparable for all individuals  Want to reduce the dimensionality of the data

School of Social and Community Medicine University of BRISTOL Multi-level models: Random-slopes model  Effect of time varies between individuals (u 1i )  The model estimates:  The regression coefficients a and b  Individuals intercepts (a + u 0i )  Individual slopes (b+u 1i )  The covariance between the intercept and slope y ij = a + u 0i + (b+u 1i )t ij + e ij y ij =weight for individual i at occasion j, time t ij

School of Social and Community Medicine University of BRISTOL Multi-level models in pictures! kCal Age Average regression line

School of Social and Community Medicine University of BRISTOL Multi-level models in pictures! kCal Age

School of Social and Community Medicine University of BRISTOL But the real world isn’t always linear...  Model the data as a curve?  Model the data as piecewise linear?

School of Social and Community Medicine University of BRISTOL What shape?

School of Social and Community Medicine University of BRISTOL What shape?

School of Social and Community Medicine University of BRISTOL Raw data

School of Social and Community Medicine University of BRISTOL

School of Social and Community Medicine University of BRISTOL Next steps  Include adjustment for over-reporting  Repeat for fat, protein, carbs, unhealthy sugars  Repeat for energy-adjusted fat, protein, carbs, unhealthy sugars

School of Social and Community Medicine University of BRISTOL Using the models: diet as the exposure  Individual-level residuals = how an individual deviates from the normal  Use in standard regression techniques  Obesity  NAFLD  Cardiovascular risk factors  etc

School of Social and Community Medicine University of BRISTOL Using the models: diet as the outcome  Include the exposure in the multilevel models  e.g. SEP  For each category of SEP, allow: 1.Different intercept 2.Different slope in each period

School of Social and Community Medicine University of BRISTOL

School of Social and Community Medicine University of BRISTOL

School of Social and Community Medicine University of BRISTOL Acknowledgements  Emma Anderson  Kate Tilling  Debbie Lawlor  ALSPAC nutrition team