Prospective relation of adolescent citrate excretion and net acid excretion capacity with blood pressure in young adulthood

Cohort profile update-overview of over 35 years of research in the Dortmund Nutritional and Anthropometric Longitudinally Designed (DONALD) study

PURPOSE

To provide an update on the cohort profile of the DOrtmund Nutritional and Anthropometric Longitudinally Designed (DONALD) study, including objectives, study design, methods and description of the comprehensive data pool, as well as to summarize the most important research findings of recent years.

METHODS

In 1985, the open (dynamic) cohort started to collect information on diet, growth, development, and metabolism of healthy children and adolescents in Dortmund, Germany. Detailed data are collected annually during infancy, childhood, and adolescence of the participants, including a 3-day weighed dietary record, a 24-h urine sample, anthropometric and medical examinations as well as interviews on lifestyle.

RESULTS

Even if the basic examination modules have not changed since the start over 35 years ago, the DONALD study has been continuously further developed by introducing new modules. As such, participants are also invited for follow-up examinations during adulthood since 2005, including an additional fasting blood withdrawal. Overall, 2375 (♂: 1177; ♀: 1198) participants were recruited in the DONALD study between 1985 and 2022. Data from ~ 30,700 anthropometric measurements, ~ 19,200 dietary records, ~ 10,600 24-h urine and ~ 1300 blood samples are available from an observation period of over 35 years.

CONCLUSION

The DONALD study provides a large data pool for longitudinal studies on nutrition, growth, and health in childhood and adolescence, its impact on the development of diseases in early adult life as well as dietary intake trends over more than three decades.

Chronic disease outcome metadata from German observational studies - public availability and FAIR principles

Metadata from epidemiological studies, including chronic disease outcome metadata (CDOM), are important to be findable to allow interpretability and reusability. We propose a comprehensive metadata schema and used it to assess public availability and findability of CDOM from German population-based observational studies participating in the consortium National Research Data Infrastructure for Personal Health Data (NFDI4Health). Additionally, principal investigators from the included studies completed a checklist evaluating consistency with FAIR principles (Findability, Accessibility, Interoperability, Reusability) within their studies. Overall, six of sixteen studies had complete publicly available CDOM. The most frequent CDOM source was scientific publications and the most frequently missing metadata were availability of codes of the International Classification of Diseases, Tenth Revision (ICD-10). Principal investigators' main perceived barriers for consistency with FAIR principles were limited human and financial resources. Our results reveal that CDOM from German population-based studies have incomplete availability and limited findability. There is a need to make CDOM publicly available in searchable platforms or metadata catalogues to improve their FAIRness, which requires human and financial resources.

Renal biomarkers of acid excretion capacity: relationships with body fatness and blood pressure

BACKGROUND

Overweight and higher BMI are known to be related to increased blood pressure (BP) and additionally associate with lowered urine pH values even at comparable total daily acid loading. Since a reduced urine pH level at a given total acid load indicates an impaired renal net acid excretion capacity (NAEC) and renal function also relates to BP, we hypothesized that NAEC may be one mediator of the body fat-BP association.

METHODS

Ammonium, titratable acid, pH, creatinine, and urea were measured in 24-h urine samples among 9-15-year-old adolescents of the DONALD Study. NAEC was determined as residual of the body surface area-corrected net acid excretion on urine pH (NAEC1) or body surface area-corrected ammonium excretion on urine pH (NAEC2). Markers of body fatness were determined anthropometrically and systolic and diastolic BP sphygmomanometrically. Multilinear regressions were used to examine cross-sectionally the body fat-NAEC and prospectively the NAEC1-BP associations.

RESULTS

All body fat parameters were inversely associated with both NAEC1 and NAEC2 among youth (P ≤ 0.01). In a separate prospective analyses, to check for possible mediation, higher adolescent NAEC1 was significantly associated with lower systolic BP in male adults only (P = 0.04), but this association was attenuated to a trend (P = 0.07) in multivariable-adjusted models.

CONCLUSIONS

Independent of systemic acid load, NAEC, i.e., the kidney's function to eliminate acids is reduced with higher body fatness, and may also contribute as a mediator in the body fatness-BP relation.

Increased body fatness adversely relates to 24-hour urine pH during childhood and adolescence: evidence of an adipo-renal axis

BACKGROUND

Reduced net acid excretion (NAE) capacity indicates a decrease in renal function. This reduction manifests as a disproportionally low 24-h urine pH in relation to the sum of actually excreted ammonium and titratable acidity by the kidney.

OBJECTIVE

The aim of this study was to test the hypothesis that higher body fatness is one determinant of kidney function impairment with a lowered urine pH even at a young age.

METHODS

NAE, pH, urea, and creatinine were measured in 24-h urine samples from 524 healthy children and adolescents (aged 6-17 y) participating in the DOrtmund Nutritional and Anthropometric Longitudinally Designed (DONALD) Study. Body fatness was assessed anthropometrically by body mass index-standard deviation score (BMI-SDS), fat mass index (FMI), body fat % (BF%), and waist circumference (WC). Multivariable linear and mixed linear regressions were used to examine cross-sectionally (n = 524 urine samples; age groups: 6-8, 9-11, 12-14, 15-17 y) and longitudinally (n = 1999 urine samples) the associations of body fatness with 24-h urine pH as the outcome variable, respectively.

RESULTS

After adjusting for the kidneys' total net acid load (24-h urinary NAE) and further relevant covariates, FMI showed significant inverse relations with urinary pH in all 4 age groups, and BMI-SDS, BF%, and WC each in 3 out of these 4 groups (P ≤ 0.02). Longitudinal results substantiated these interindividual relations and further showed intraindividual increases in body fatness to be paralleled by urine pH decreases (P ≤ 0.0002).

CONCLUSIONS

Independent of underlying acid load, an early increase in body fatness is associated with increased free proton excretion, and thus with a decline in the kidney's acid excretion function, which could potentiate the risk of renal nephrolithiasis.