In the Rancho Bernardo Study (depicted), women that had a low birth weight and were obese as adults had the highest prevalence of the metabolic syndrome (about 30%). Other studies have also reported an interaction between low birth weight and measures of adult obesity. For example, the study by Hales and colleagues, previously mentioned, found that the highest prevalence of impaired glucose tolerance and diabetes was seen in those who were small at birth and obese as adults. In a South Wales study population, the association between low birth weight and coronary heart disease was entirely restricted to those who had a high body mass index in adulthood (Frankel S, et al., 1996).

The Pima Indians are another study population where the potential for effect modification was examined. Investigators found that birth weight was inversely related to subsequent development of diabetes only among infants that were not breastfed. These studies suggest that the relationship between birth weight and the adult metabolic syndrome may be modified substantially by the presence of other risk factors, findings that are important for identifying opportunities for prevention.