Plasma beta-carotene is not a suitable biomarker of fruit and vegetable intake in german subjects with a long-term high consumption of fruits and vegetables.
Garcia AL, Mohan R, Koebnick C, Bub A, Heuer T, Strassner C, Groeneveld MJ, Katz N, Elmadfa I, Leitzmann C, et al. Ann Nutr Metab. 2010; 56(1):23-30. Epub 2009 Nov 27.