1 / 5Indian gooseberry has been used by Ayurvedic practitioners for centuries to treat various health ailments. This small green fruit is one of the best sources of vitamin C. About 20 times more vitamin C is found in one gooseberry than in orange. 2 / 5One medium-sized orange (100 grams) contains 53.2 milligrams of vitamin C. The antioxidant properties of citrus fruits may help promote immune health. Oranges are also good when suffering from colds and other allergies. 3 / 5Lemon is one of the most widely available sources of vitamin C and other antioxidants. It can help strengthen the immune system. Antioxidants help the body remove free radicals that can damage cells.4 / 5Chili contains the same amount of vitamin C as any other citrus fruit. This vegetable is also a good source of beta carotene. The minerals and vitamins present in it can enhance the body's immune system. It also helps in keeping the eyes healthy and reducing oxidative stress.5 / 5Pineapple has been used for centuries to treat digestive and inflammatory problems. It contains high amounts of vitamin C and manganese. It is also low in calories and rich in dietary fiber and bromelain. Both viral and bacterial infections can be prevented by eating pineapple daily.