| dc.description.abstract | Background: Folate (vitamin B9) and vitamin B12 (B12) are essential nutrients for maintaining normal haematological and neurological function as well as preventing birth defects. There are indications that Norwegian women of childbearing age have low folate status, and there is continuous debate on whether to initiate mandatory folic acid foritfication. Further, in line with the Nordic Nutrition Recommendations 2023, the proportion of individuals eating plant-based is increasing, thereby reducing the consumption of the main dietary sources of B12. Thus, there is interest in assessing recent trends in folate and B12 status in Norwegian adults. Methods: Data on serum folate, B12, plasma total homocysteine (tHcy) and plasma methylmalonic acid (MMA) analysed by Fürst Medical Laboraties were obtained. Over one million blood samples from 675,189 subjects aged 18 to 50 years who attended their general physician between 2000 and 2019 were analysed. Adjusted menas (estimated marginal means) and changes in metabolite concentrations between 2000-2004 and 2015-2019 were calculated using linear mixed models controlling for estimated glomerular filtration rate (eGFR), sex and age group, with random terms accounting for variation within subjects and within the laboratory methods of quantification. Results: Women accounted for 52.9% of the sample and the geometric mean (geometric SD) age was 34.8 (1.32) years. The adjusted mean (95% CI) serum folate concentration decreased from 14.0 (13.0, 15.1) to 13.2 (12.3, 14.2) nmol/L between the two time periods, and serum B12 increased from 300 (294, 306) to 326 (319, 333) pmol/L. Plasma tHcy decreased from 11.3 (10, 12.8) to 10.1 (8.9, 11.4) µmol/L, while plasma MMA concentrations were relatively stable around 0.16 µmol/L. Folate decreased most dramatically in men (15%), with a corresponding 10% increase in tHcy. Women experienced a 5% decrease in folate concentrations and a 10% decrease in tHcy. In 2015-2019, 45.7% of all subjects had elevated plasma tHcy. Over 80% of women of reproductive age had folate concentrations below the World Health Organization (WHO) recommendation of 25.5 nmol/L, and over 20% were deficient (<10 nmol/L). Serum B12 concentrations were satisfactory, using serum B12 <221 pmol/L as a cutoff for low status. Conclusion: Overall, folate status decreased and B12 status increased in Norwegian adults attending their general physician between 2000 and 2019. Folate status was concerning in both men and women, and plasma tHcy elevated in a significant proportion of the population. | eng |