Public Health Nutrition: 13(1), 54–62 doi:10.1017/S1368980009005904 Exploration of biomarkers for total fish intake in pregnant Norwegian women Anne Lise Brantsæter 1, *, Margaretha Haugen 1 , Yngvar Thomassen 2 , Dag G Ellingsen 2 , Trond A Ydersbond 3 , Tor-Arne Hagve 4,5 , Jan Alexander 1 and Helle Margrete Meltzer 1 1 Division of Environmental Medicine, Department of Food Safety and Nutrition, Norwegian Institute of Public Health, PO Box 4404 Nydalen, NO-04030 Oslo, Norway: 2 National Institute of Occupational Health, Oslo, Norway: 3 Statistics Norway, Oslo, Norway: 4 Department of Medical Biochemistry, Rikshospitalet University Hospital, Oslo, Norway: 5 Faculty Division Akershus University Hospital, University of Oslo, Oslo, Norway Submitted 4 April 2008: Accepted 4 March 2009: First published online 3 June 2009 Abstract Objective: Few biomarkers for dietary intake of various food groups have been established. The aim of the present study was to explore whether selenium (Se), iodine, mercury (Hg) or arsenic may serve as a biomarker for total fish and seafood intake in addition to the traditionally used n-3 fatty acids EPA and DHA. Design: Intake of fish and seafood estimated by an FFQ was compared with intake assessed by a 4 d weighed food diary and with biomarkers in blood and urine. Setting: Validation study in the Norwegian Mother and Child Cohort Study (MoBa). Subjects: One hundred and nineteen women. Results: Total fish/seafood intake (median 39 g/d) calculated with the MoBa FFQ was comparable to intake calculated by the food diary (median 30 g/d, r S 5 0?37, P , 0?001). Erythrocyte DHA and blood Hg, Se and arsenic concentrations were positively correlated with intake of fish and seafood, but the association for DHA was weakened by the widespread use of supplements. The main finding was the consistent positive association between the intake of fish/seafood and blood arsenic concentration. In multivariate analyses, blood arsenic was associated with blood Hg and fish and seafood intake. In these models, arsenic turned out to be the best indicator of intake of fish and seafood, both totally and in subgroups of fish/seafood intake. Conclusions: While DHA reflected the intake of fatty fish and n-3 PUFA supple- ments, blood arsenic concentration also reflected the intake of lean fish and seafood. Blood arsenic appears to be a useful biomarker for total fish and seafood intake. Keywords Biomarkers Fish and seafood intake Pregnant women Blood arsenic Erythrocyte DHA Assessing trends in eating habits and dietary patterns is an essential component in the surveillance of population health and the development of dietary advice and inter- ventions. Dietary monitoring requires a tool validated in the target population, and biomarkers of dietary exposure may assist in uncovering the errors associated with the method in use (1) . For a biomarker to be used for valida- tion of a dietary instrument, it should have a strong direct and independent relationship with the nutrient or food group of interest. Recovery biomarkers, like doubly labelled water (2) and urinary N (3) , are less influenced by the body’s homeostatic control than concentration bio- markers, which are extensively used in spite of their weaker association with consumption (4) . Biomarkers that reflect the intake of a food group rather than a specific nutrient are scarce. Plasma car- otenoids and urinary flavonoids have been used as bio- markers of fruit and vegetable groups (5,6) and plasma or tissue n-3 PUFA, mainly EPA and DHA, have been used as biomarkers of both total fish and fatty fish intake (7,8) . However, as lean or semi-lean fish and seafood comprise nearly two-thirds of the total fish intake in Norway (9) ,a biomarker related to total fish/seafood intake rather than fatty fish and fish-oil supplements could contribute to better validation of this food group than EPA or DHA. Dietary fish and seafood are rich sources of the essential trace elements iodine and Se, but are also a major source of methylmercury and arsenic (10,11) . The presence of methylmercury in human tissues has been shown to be directly related to intake of fish and sea- food (10) , whereas the relationship between blood arsenic, blood Se and intake of fish and seafood has been inves- tigated less. Arsenic in fish and seafood is predominantly present in the organic form arsenobetaine. Organic forms of arsenic are considered non-toxic compared with inorganic arsenic from airborne industrial emissions and *Corresponding author: Email anne.lise.brantsaeter@fhi.no r The Authors 2009 https://doi.org/10.1017/S1368980009005904 Published online by Cambridge University Press