MacDonald , H M , Hardcastle , A C , Duthie , G G , Duthie , S J , Aucott , L , Sandison , R , Shearer , M J & Reid , D M 2009 , ' Changes in vitamin biomarkers during a 2-year intervention trial involving increased fruit and vegetable consumption by free-living volunteers ' , British Journal of Nutrition , vol. 102 , no. 10 , pp. 1477-1486 . https://doi.org/10.1017/S0007114509990377