Superoxide dismutase has been found in almost all organisms living in the presence of oxygen, including some anaerobic bacteria, supporting the notion that superoxide is a key and general component of oxidative stress.
   In aerobic cells, free radicals are constantly produced mostly as reactive oxygen species. Once produced, free radicals are removed by antioxidant defenses including the enzymes catalase, glutathione peroxidase, and superoxide dismutase. Reactive oxygen species, including nitric oxide and related species, commonly exert a series of useful physiological effects. However, imbalance between prooxidant and antioxidant defenses in favor of prooxidants results in oxidative stress. This results in damage to lipids, proteins, and nucleic acids. Alone or in combination with primary factors, free radicals are involved in the cause of hundreds of diseases.

Superoxide Dismutase supplements - do they work?
There are vitamin companies selling supplements that they claim to have superoxide dismutase. I am not aware of any studies regarding the ingestion of a superoxide dismutase supplement and its effect on health. Does this enzyme get absorbed intact from the gastrointestinal system? If it does, does it then make its way to the cells in the body and function similar to the intrinsic superoxide dismutase within our cells? Are there side effects to its use? Is it safe? i personally have not seen any such research to know whether taking a SOD supplement is useful. Hopefully some organization will do such research and we can have a better idea as to whether taking such a supplement is beneficial.
   I have also seen supplements promoted to increase superoxide dismutase levels in the body. Again, I have not come across any human research that these superoxide dismutase enhancing supplements are effective, and if they are, which medical conditions they would be appropriate to prescribe.

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Different types of SOD
Three forms of superoxide dismutase are found in humans. SOD1 is located in the cytoplasm, SOD2 in the mitochondria and SOD3 is outside of the cell. SOD1 and SOD3 contain copper and zinc, while SOD2 has manganese.

Superoxide Dismutase outside of the cell
Extra cellular superoxide dismutase ( EC-SOD ) catalyzes the dismutation of superoxide radical to hydrogen peroxide and oxygen in the interstitial spaces of tissues and in extracellular fluids (plasma, lymph, and synovial fluid). It eliminates superoxide radicals from the cell environment and prevents the formation of reactive oxygen species and their derivatives. EC-SOD is a secretory, tetrameric glycoprotein containing copper and zinc, with a high affinity to certain glycosaminoglycans, such as heparin and heparan sulfate. It plays an important role in maintaining vascular tone, lung function, and the metabolism of NO, and in the pathology of such diseases as atherosclerosis, diabetes, and arthritis.

Superoxide Dismutase and amyotrophic lateral sclerosis
In the mid 1990s, the linkage between mutations in the gene coding for the antioxidant enzyme Cu,Zn superoxide dismutase (SOD1) and the neurodegenerative disease known as familial amyotrophic lateral sclerosis was established.

Herbs that influence Superoxide
There are herbs and nutrients that influence antioxidant levels. With time I will mention others, for the time being I wanted to present one example:
Extract of Andrographis paniculata inhibits formation of oxygen derived free radicals such as superoxide and hydroxyl radicals.

Superoxide Dismutase Research Update
Vascular protection: superoxide dismutase isoforms in the vessel wall.
Arterioscler Thromb Vasc Biol. 2004 Aug;24(8):1367-73. Faraci FM, Didion SP.
Department of Internal Medicine, Cardiovascular Center, University of Iowa, Carver College of Medicine, Iowa City, IA
Blood vessels express 3 isoforms of superoxide dismutase : cytosolic or copper-zinc superoxide dismutase (CuZn-SOD), manganese superoxide dismutase (Mn-SOD) localized in mitochondria, and an extracellular form of CuZn- superoxide dismutase (EC-SOD). Because there are no selective pharmacological inhibitors of individual superoxide dismutase isoforms, the functional importance of the different SODs has been difficult to define. Recent molecular approaches, primarily the use of genetically-altered mice and viral-mediated gene transfer, have allowed investigators to begin to define the role of specific superoxide dismutase isoforms in vascular biology. This review will focus mainly on the role of individual superoxide dismutase in relation to endothelium under normal conditions and in disease states. This area is important because reactive oxygen species and superoxide anion are thought to play major roles in changes in vascular structure and function in pathophysiology.

Superoxide Dismutase questions
Q. I get a Puritan's Pride catalog and they have listed SOD 250 mg tablets (superoxide dismutase) equivalent to 2000 units of activity. The say that SOD (superoxide dismutase) is an enzyme that can be found in human cells. Does this product work?
     A. I can't say for sure since I have not come across any studies evaluating the role of a superoxide dismutase supplement in human health. I would be surprised if the SOD in this product were absorbed and transported into cells where it could do its work. At this time I personally would not buy this product since there is no evidence that it would be effective. And I have no idea what they mean by 2000 units of activity. Activity where? It is not clear to me how the activity of this enzyme is determined and how do we know the 2000 unit activity will influence our cellular metabolism. Perhaps you could contact the research department at Puritan's Pride and ask them to explain how this superoxide dismutase supplement is supposed to work and perhaps they have some research papers that I am not familiar with. If any researchers out there know more about this topic, please contact me, I am very interested.
   I have also seen a Source Naturals superoxide dismutase product that has 2000 units of this antioxidant.