DAG4 is one of Lifelines' additional assessments performed in collaboration with the UMCG department of genetics (see also: DAG1, DAG2 and DAG3). DAG is the abbreviation of DArmGezondheid, or “Gastrointestinal health” in Dutch.

There is increasing insight into the role of bacterial composition in the intestine and upon the occurrence of (chronic) diseases. Previous research in DAG1 (DEEP) demonstrated the relation of the microbiome and lipids, but also many other diseases and intrinsic and extrinsic factors. Previous research in DAG3 (DAG3) described the gut microbioom in a larger cohort.

Longitudinal analyses in 350 Lifelines DEEP participants that were also part of the DAG3 collection, showed that microbiome individual specific patterns could be stable for >3 years. However, it was also observed that some microbial changes were related to individual’s changes over time were in line with individual’s changes in their healthy status, lifestyle and medication usage (REFERENCE).

The purpose of DAG4 was to extent the amount of participants with longitudinal data and longitudinal biological samples, that gives an unique opportunity to study the long-term dynamics of the gut microbiome and its relation to developing and progressing of diseases and phenotypes.

A total of approximately <NUMBER> participants were included in the DAG4 dataset:

• Alle participants we aged 18 years or older.
• … participants were also included in the (DEEP) dataset
• … participants were also included in the (DAG3) dataset
• ~… participants were genotyped in the UGLI project.

Besides the samples used to generate the microbiome data, questionnaires were also sent to participants to gather phenotypic data on gastrointestinal health symptoms by means of Rome III criteria questionnaire (Longstreth etal 2006) and the Bristol Stool Form Scale (O’Donnell etal 1990).

Participants who were invited for assessment 3A according to the regular Lifelines invitation process were asked to also participate in this study. In addition to the regular 2A measurements, DAG3 participants underwent the following steps:

3A Visit 1

• Hand over written stool collection instructions and collection material

3A Visit 2

• Hand in collected stool