Most people consume vitamins and supplements to boost their bodily functions. Vitamin C, for instance, is a natural antioxidant that fights cell-damaging free radicals in the body. Some food supplements actually harm the body by reducing antibodies -- the proteins that the body produces to attack antigens such as bacteria, fungi or viruses that cause illness. Although vitamin C and other nutrients can fight disease, there are some supplements that affect the body's immune system negatively by reducing antibodies.
Omega-6 Fatty Acids
Omega-6 fatty acid is one of the chemicals necessary for survival that the body is incapable of producing. Foods high in omega-6 fatty acids, including oils, shortening, walnuts and sunflower seeds, can also negatively impact immune response. The European Union Food Information Council reports that diets high in fat can harm immune response by suppressing antibody production. The council's report states, "Diets that are high in fat seem to depress the immune response and thus increase the risk of infections. Reducing fat content in the diet can increase immune activity."
Vitamins and Calcium from Milk
Milk is one of the best nutritional sources of calcium, and vitamins A and D. People who drink milk for calcium and vitamins also feel the effects of bovine growth hormones fed to dairy cattle. These hormones, which are used to increase milk production, may reduce immune response. The Physicians for Social Responsibility cite a Health Canada study, which found negative immune system responses in 20 to 30 percent of laboratory animals tested.
Vitamins and Supplements with Gluten
Over-the-counter nutritional supplements are typically coated to prevent indigestion. The coating typically contains gluten, a health hazard for people diagnosed with celiac disease. Celiacs have a digestive intolerance to gluten, rendering coated vitamins a hindrance rather than a help. People with celiac disease that consume gluten shred their own immune system. When digested and dispersed in the bloodstream, gluten triggers the immune system to release specific anti-gluten antibodies. These antibodies become confused and begin attacking healthy tissues and other antibodies in the bloodstream. The cannibalization of the antibodies renders the nutrition gained from the gluten-coated vitamin useless.