Williams, I.O., R.S. Parker, and J. Swanson. 2009. “Vitamin A Content of Southeastern Nigerian Vegetable Dishes, Their Consumption Pattern and Contribution to Vitamin A Requirement of Pregnant Women in Calabar Urban, Nigeria”. Pakistan Journal of Nutrition 8 (7): 1000–1004. https://doi.org/10.3923/pjn.2009.1000.1004.