I. Williams, R. Parker, and J. Swanson, “Vitamin A Content of Southeastern Nigerian Vegetable Dishes, Their Consumption Pattern and Contribution to Vitamin A Requirement of Pregnant Women in Calabar Urban, Nigeria”, Pak. J. Nutr., vol. 8, no. 7, pp. 1000–1004, Jun. 2009, doi: 10.3923/pjn.2009.1000.1004.