Pfeiffer Christine M., Schleicher Rosemary L., Johnson Clifford L., and Coates Paul M. 2012. “Assessing Vitamin Status in Large Population Surveys by Measuring Biomarkers and Dietary Intake - Two Case Studies: Folate and Vitamin D”. Food & Nutrition Research, April. https://doi.org/10.3402/fnr.v56i0.5944.