The vitamin A required by the human body can be obtained not only directly from animal foods but also from the conversion of beta-carotene from plant-based foods. There is sufficient evidence to show that after consuming beta-carotene, its conversion efficiency to vitamin A is sufficient to meet the body's needs for vitamin A.
Moreover, most importantly, the beta-carotene that is not converted into vitamin A also has other important physiological functions. It has antioxidant effects, which are significant for preventing cardiovascular diseases and tumors, as well as for delaying aging. In other words, beta-carotene can not only be converted into vitamin A but also has antioxidant effects that vitamin A does not possess. Therefore, foods rich in beta-carotene, such as vegetables like broccoli, carrots, pumpkins, chives, spinach, tomatoes, shepherd's purse, and sweet potatoes, as well as fruits like citrus, are the best sources of vitamin A.
In comparison, foods rich in vitamin A, such as animal liver and other organs, egg yolks, and lean meat, contain relatively high levels of cholesterol or saturated fat. Therefore, it is not wise to eat a lot of pork liver for eye protection. One should eat more fresh, dark-colored vegetables and fruits.