Vitamin C is found in natural foods like oranges, tomatoes, bell peppers, kale, broccoli, brussels sprouts, cauliflower and strawberries. It can help the immune system, wound healing, collagen production and weight management. Vitamin C is also an antioxidant that helps protect cells from free radical damage. Vitamin C also helps absorb iron from food. A lack of Vitamin C can lead to health problems in dogs like decreased protection from infection and delayed wound healing.