Vitamin C is well known for playing a role in immune health and is found naturally in fruits and vegetables, especially citrus fruits, red peppers, green peppers, broccoli, strawberries and brussels sprouts. The vitamin encourages wound healing, preventing cell damage and building collagen. If you’re feeling fatigued, experience poor wound healing or loose teeth, you may not be eating enough of the foods listed and may consider supplementation in the form of an injection.