Context: Higher mean and rapid increases in body mass index (BMI) during infancy are associated with subsequent obesity and may be influenced by exposure to endocrine-disrupting chemicals such as phenols.

Objective: In a prospective US-based cohort conducted 2010-2014, we investigated associations between environmental phenol exposures and BMI in 199 infants.

Methods: We measured 7 urinary phenols at ages 6-8 and 12 weeks and assessed BMI z-score at up to 12 study visits between birth and 36 weeks. We examined individual and joint associations of averaged early infancy phenols with level of BMI z-score using mean differences (β [95% CI]) and with BMI z-score trajectories using relative risk ratios (RR [95% CI]).

Results: Benzophenone-3, methyl and propyl paraben, and all phenols jointly were positively associated with higher mean BMI z-score (0.07 [-0.05, 0.18], 0.10 [-0.08, 0.27], 0.08 [-0.09, 0.25], 0.17 [-0.08, 0.43], respectively). Relative to a stable trajectory, benzophenone-3, 2,4-dichlorophenol, 2,5-dichlorophenol, and all phenols jointly were positively associated with risk of a rapid increase trajectory (1.46 [0.89, 2.39], 1.33 [0.88, 2.01], 1.66 [1.03, 2.68], 1.41 [0.71, 2.84], respectively).

Conclusion: Early phenol exposure was associated with a higher mean and rapid increase in BMI z-score across infancy, signaling potential long-term cardiometabolic consequences of exposure.