You know vitamin C can help you prevent colds, but did you also know that it works as a natural antihistamine?   If you suffer from allergies, you should consider Vitamin C, as it is a natural antihistamine capable of blocking the effects of inflammatory substances that some people produce in response to allergens such as pollen and pet dander.  Allergies are frequently an underlying reason of sinusitis and may also cause the intensely itchy rashes associated with eczema.  Vitamin C, along with other antioxidants could help these conditions.Interestingly, vitamin C can help prevent or improve asthmatic symptoms as well; several studies have demonstrated that asthma sufferers are often deficient in vitamin C and other vitamins.  Further, vitamin C could stave off an exercise induced asthma attack if an adequate dose (typically between 500mg and 5000mg) of vitamin C is taken right before a workout1.