Markers for nutrition studies: review of criteria for the evaluation of markers.

Introduction: Markers are important tools to assess the nutrition status and effects of nutrition interventions. There is currently insufficient consensus in nutrition sciences on how to evaluate markers, despite the need for properly evaluating them.

Objectives: To identify the criteria for the evaluation of markers related to nutrition, health and disease and to propose generic criteria for evaluation.

Method: The report on "Evaluation of Biomarker and Surrogate Endpoints in Chronic Disease" from the Institute of Medicine was the starting point for the literature search. Additionally, specific search strategies were developed for Pubmed.

Results: In nutrition, no set of criteria or systematic approach to evaluate markers is currently available. There is a reliance on the medical area where statistical methods have been developed to quantify the evaluation of markers. Even here, a systematic approach is lacking-markers are still evaluated on a case-by-case basis. The review of publications from the literature search resulted in a database with definitions, criteria for validity and the rationale behind the criteria. It was recognized that, in nutrition, a number of methodological aspects differ from medical research.

Conclusions: The following criteria were identified as essential elements in the evaluation of markers: (1) the marker has a causal biological link with the endpoint, (2) there is a significant association between marker and endpoint in the target population, (3) marker changes consistently with the endpoint, e.g., in response to an intervention, and (4) change in the marker explains a substantial proportion of the change in the endpoint in response to the intervention.