DAG3 is one of Lifelines' additional assessments performed in collaboration with the UMCG department of genetics (see also: DAG1 and DAG2). 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. The purpose of DAG3 was to gather additional data and biological samples from Lifelines participants to answer research questions such as:

• ‘What is the role of the microbiome in the occurrence of chronic diseases?’
• ‘What is the relation between genetic variants, methylation, gene expression and metabolite levels?’

A total of 9500 participants were included in the DAG3 dataset:

• 700 were children aged 8-17 years
• 400 participants were also included in the (DEEP) dataset
• microbiome collection sites were more diverse
• ~9000 participants were genotyped in the UGLI project.

Metagenomic sequencing of the Lifelines DAG3 samples is underway to assess taxonomy, strain diversity and functionality. Uniquely, not only are all individuals fully genotyped but glycerol aliquots of their microbiota are also stored to enable bacterial culture for further functional studies. Lifelines DAG3 will have the power to study host-microbe interactions and will also allow studies to move from association to causality ¹⁾.

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

The following variables were collected: