Early Life Determinants of Skeletal Maturation and Endocrine Health in Young Adults - A Nationwide Birth Cohort Study

Population-based, nationwide, cross-sectional, clinical study with already available early life exposure data including bio banked neonatal biological samples. An embedded design using the full 2006+2007 birth cohorts is used to demonstrate external validity of the clinically assessed cohort. We will obtain the necessary ethics and regulatory approval and individual consent from the participants who are all aged 18.

The overall aim of the project addresses whether the following sets of potential determinants are associated with young adult hormonal status, lipids, bone turnover markers, bone mineral density (BMD), fat mass and lean body mass at age 18 years: a) maternal risk factors during preconception and pregnancy; b) risk factors at birth; c) neonatal epigenetic signature; d) childhood risk factors.

Aim 1 - Epigenetics - Is peak bone mass and body size influenced by epigenetic profile for endocrine signals at birth? From the second trimester of pregnancy and until early adulthood, bone is gradually developed and shaped, with longitudinal growth dominating the later stages of fetal life, infancy, and childhood. This is followed by a period of rapid bone mineral accrual occurring up to and during puberty, with bone mass accretion ultimately reaching a plateau in young adult life. It is strongly suggested by prior research that epigenetic variation at birth can result from differences in maternal health, lifestyle, nutrition, smoking and medication usage and result in long-term changes in gene expression and metabolism.

As existing childhood cohorts either lack BMD information, suffer from significant cohort attrition, and low recruitment success, there is an opportunity to instead use national invitations to recruit directly into an efficient endocrine and bone outcomes study and use already archived biological material from early infancy and register data and obtain individual study subject consent.

Aim 2 - Endocrine status in young adulthood - Does maternal medication use and health issues prior to pregnancy or in pregnancy affect endocrine health in young adults? This question will be addressed using data from Danish national registers. While it is straightforward to link binary events data e.g., malformations or paediatric admissions (eg epilepsy, diabetes, failure to thrive) to registry capture of their maternal exposures, we will be obtaining detailed information about continuous outcomes including endocrine serum biochemistry (thyroid axis, GH axis, PTH-vitamin D-calcium axis, lipids, HbA1c), hair cortisol levels (a cumulative serum cortisol metric) as well as body composition and bone density metrics.