Targeted Nutritional Therapies
Vitamin C. Another study investigated antioxidant activity in the lens and vitreous of diabetic and non-diabetic subjects. Researchers found significantly decreased glutathione peroxidase activity and lower vitamin C (ascorbic acid) levels in the lenses of diabetic patients, especially in the presence of retinal damage. Ascorbic acid is known to exert important antioxidant functions in the eye compartment. This study indicated that oxidative damage is involved in the onset of diabetic eye complications, in which the decrease in free radical scavengers was shown to be associated with oxidation of vitreous and lens proteins (Altomare 1997).
Vitamin B12. Vitamin B12 (cyanocobalamin, methylcobalamin or hydroxycobalamin [a naturally occurring form]), is critical for several functions, such as folate metabolism, myelin synthesis, and normal development of red blood cells. A lack of this vitamin may leave the optic nerve more susceptible to damage. Studies have suggested that marginal vitamin deficiency plays an indirect, but important role in the development of diabetic complications (Anon 1990).
Vitamin E. One study showed that reducing lipid peroxidation stress of the erythrocyte membrane using vitamin E (alpha-tocopherol nicotinate) therapy may be useful in slowing deterioration of microangiopathy in Type II diabetes mellitus. The dose used was 300 mg, 3 times daily (after meals) for 3 months (Chung 1998). Researchers reported that vitamin E supplements normalized blood flow to the retina and kidneys. Following a 4-month clinical trial in which subjects were given doses of vitamin E that were 60 times the recommended daily allowance, kidney function improved and blood flow to the retina was increased almost to the normal rate. A large follow-up clinical trial was recommended (Bursell 1999).
Another study evaluated the use of antioxidants as a prophylactic for eye disorders, such as macular degeneration, cataracts, ROP, and cystic macular edema. The study points to the positive role of antioxidants in both experimental research and clinical observations (KaLuzny 1996).
Green Tea. Green tea is another potent antioxidant that could be of use in the treatment of retinopathy. The active compound in green tea is catechins. Powerful polyphenolic antioxidants, catechins are astringent, water-soluble compounds that can be easily oxidized. They are a subgroup of flavonoids, weak phytoestrogenic compounds widely available in vegetables, fruit, tea, coffee, chocolate, and wine. The antioxidant potential of both green and black teas, as measured by the Phenol Antioxidant Index, was found to be significantly higher than that of grape juice and red wine. Green tea also has anti-angiogenic properties, indicating it could be used for prevention and possibly treatment of degenerative eye disorders (eg, diabetic retinopathy) that also depend on the development of new blood vessels (Zigman 1999; Thiagarajan 2001).
Silibinin. An in vitro study showed that silibinin (milk thistle extract) can normalize the degree of ribosylation and sodium pump activity, even in the presence of abnormally high glucose levels (Di Giulio 1999). A similar protective effect of silibinin against ribosylation was found in the retina (Gorio 1997). Thus, silibinin may be able to decrease the extent of diabetic neuropathy and retinopathy, two extremely serious complications of diabetes. Considering that silibinin has also been shown to protect the kidneys, another organ seriously damaged by glycation (kidney failure is a frequent cause of death in diabetics), silibinin should be seriously explored as an adjunct treatment in diabetes.
Propionyl-l-carnitine. Research examined the effect of propionyl-L-carnitine (an analogue of L-carnitine) on retinopathy in rats with laboratory-induced diabetes. Findings pointed to a potential therapeutic value of propionyl-L-carnitine for diabetic retinopathy (Hotta 1996). L-carnitine, a natural substance found in meat, is related to B vitamins.