A Study of the Impact of Environmental Chemicals and Micronutrients on Pubertal Development in A Mexican Population

Puberty is one of the most important developmental milestones in life, involving complex physical and psychological changes. A trend towards earlier puberty has been well documented since the early 20th century. The decline in the pubertal age requires special attention due to its implications for long-term health outcomes with increased risks of reproductive cancers, type-2 diabetes, cardiovascular diseases, and psychological sequelae, and hence is a major public health concern. Increasing evidence suggests that environmental chemicals and nutrition may contribute to the trend towards earlier sexual maturation. Exposures that occur at susceptible developmental periods may impact the prenatal growth trajectory and development of the reproductive axis and potentially have long-term effects on the tempo of maturation later in life. Therefore, it is of public health importance to examine these modifiable elements at early life to improve the understanding of pubertal disorders and their link to adverse health conditions. The objectives of this dissertation were to determine whether exposures to environmental chemicals such as fluoride, lead and nutritional factors such as micronutrients at multiple life stages including in utero, early childhood and peripuberty are potential determinants of sexual maturation by using mother-offspring pairs from the Early Life Exposure in Mexico to ENvironmental Toxicants (ELEMENT) cohorts. We found that prenatal fluoride exposure during pregnancy was not associated with development of secondary sex characteristics directly, but associated with reduced peripubertal serum testosterone in boys and with increased peripubertal serum IGF-1 (insulin-like growth factor 1) in girls. Increased maternal consumption of selenium and zinc during pregnancy was related to advanced pubic hair growth, and increased maternal consumption of phosphorus and riboflavin during pregnancy was related to advanced genital development in boys. A significant negative association of prenatal and early childhood lead exposure with pubertal development was observed in girls. Our findings suggest that fluoride, lead, and intakes of micronutrients during early life may have long-term impacts on development of sexual maturation in adolescents, particularly in a sex-specific fashion. This work highlights the need for more research to examine associations between environmental factors during sensitive periods of development and sexual maturation to better understand pubertal disorders and their long-term consequences.PhDNutritional SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/137165/1/yunliu_1.pd