The aims of the proposed project are to assess the effects of exposure to soy-based infant formula in infancy on 1) vocabulary acquisition in males and females at ages 15 and 24 months, and 2) the time to onset of puberty in males and females. The rationale for this investigation is that soy-based infant formula contains hormonally active phytoestrogen compounds (specifically, genistein and daidzein) which may have the capacity to influence various aspects of neurological and physical development. It is of particular interest to observe how early life exposure to these estrogenic compounds may differentially effect development in boys and girls.

The longitudinal nature of the ALSPAC data makes it an ideal resource for looking at the effects of early life exposures on developmental outcomes occuring later in childhood. This data set contains infant feeding data that would inform us with respect to our exposure of interest [soy, or 'soya,' formula]. Additionally, ALSPAC documentation indicates that vocabulary has been assessed at both 15 and 24 months using the MacArthur-Bates Communicative Development Inventories. Ideally, these vocabulary outcome measures will be combined to develop language acquisition trajectories that can be analyzed via mixed model regression to compare rates across exposures and genders. Multiple measures of pubertal onset (age at menarche, Tanner staging) have also been repeatedly assessed at 5 time points between 97 and 157 months. Survival analysis will be implemented in the analysis of time to onset of puberty.

We do recognize that the prevalence of soy-based infant formula usage is lower in the UK than in the United States, and expect that this will be reflected to some degree in the ALSPAC data. However, given the substantial size of the ALSPAC cohort, we are confident that the proportion of soy exposed infants in ALSPAC will be sufficiently informative and allow for the conduct of sound and meaningful analyses.

An alternative design would be to conduct a randomized control trial of soy-based formula, cow milk formula and breast milk infant feeding regimes. However, this alternative study method is not feasible for the current investigators due to time and other resource limitations. Time is particularly prohibitive for our second outcome of intrest (time to onset of puberty), where approximately 10 or more years would be necessary for all relevent data to be collected. Given that the ALSPAC data has already been collected, using it in the proposed study is certainly the most effecient approach possible.