Objectives: The aim of the present study was to investigate whether the following four markers: vitamin B12, selenium, vitamin D, and parvalbumin may be used as compliance markers for fish intake.
Methods: Blood samples from a randomized cross-over herring intervention study (n = 32) were analysed by HPLC and immunochemistry. The criteria were that plasma or serum concentrations of candidate compliance markers after the herring diet should increase significantly compared to starting concentrations. In addition, the reference meat diet should not yield an increase in plasma concentration of the candidate marker.
Results: Vitamin B12 and selenium met the set criteria for indicating a correlation between the marker and fish intake with significant increases in serum concentrations at 8.9% (p = 0.008) and 4.6% (p = 0.02), respectively, after a 6-week herring intervention (5 meals a week). Parvalbumin and 25-hydroxy vitamin D3 levels did not increase significantly after the herring interventions.
Conclusions: Vitamin B12 may be suitable as a compliance marker for fish intake. Although selenium also met the criteria, the change in selenium serum concentrations was small compared to the change in vitamin B12 levels.