It is widely claimed that body mass index (BMI) is a poor measure of adiposity since it does not directly measure fat mass and does not give an indication of fat distribution. Measurements of central adiposity such as waist circumference or waist:hip circumference are said to be better predictors of adverse metabolic outcomes and more direct measurements of total or regional fat mass (such as obtained by DXA, MRI or CT scanning) are thought to better predict adverse outcomes than BMI. However, simple measurements of height and weight (that are used to derive BMI) are more feasible to complete in clinical and public health practice than methods that involve radiological examination, and BMI assessment is also likely to be easier and more reliable than measuring waist and hip circumference in clinical or public health practice. It is also possible that the best measure of adiposity (with respect to predicting adverse outcomes) differs by age and gender. To our knowledge very few studies have directly compared the magnitudes of association of BMI with other measurements of adiposity/fat distribution to determine the extent to which BMI may underestimate true associations with adverse outcomes. Several studies in adults have compared BMI and waist or waist to hip circumference but these have rarely made appropriate direct comparisons of standardised measurements. They have tended to include both measurements in multivariable models and conclude that the one remaining statistically significant is the better measurement. To our knowledge no study has attempted to make such comparisons across a range of cohorts of different ages. The aim of this project is to compare the magnitudes of association of different measurements of adiposity/fat distribution with metabolic and vascular outcomes and all-cause mortality (outcomes will vary and be appropriate to the cohort) in cohorts of different ages. Overall the project will use data from BWHHS, ALSPAC, Caerphilly, Speedwell, Boyd Orr (pending relevant permissions).

The specific aims of ALSPAC are:

1. To compare the magnitudes of association of BMI; waist circumference and DXA total and trunkal fat mass (all standardised), as measured at age 11 with each of the following outcomes:

a. Fasting insulin, glucose, lipids assessed at age 15

b. Blood pressure assessed at age 11, 13 and 15

We propose using anthropometry assessed at age 11 because a recent prosepective study (and meta-analysis presented at DoHAD conference) suggest clear associations of BMI assessed at this age and older in both girls and boys with future CHD risk. We think it important to assess associations with prospective outcomes but fasting blood assays for lipids, glucose and insulin are only available at age 15. Blood pressure will be assessed cross-sectionally (age 11) but also at 2 years and 4 years from the anthropometric assessment.

The final paper will have Amy Taylor as first author and Debbie Lawlor as last (supervising author) and co-authors from each study. We would be grateful if you could let us know who would be appropriate to include as co-authors from ALSPAC.