Preventing Diabetic Cataracts Naturally
Research indicates that this simple nutritional strategy may benefit your diabetic patients.
By Joseph Freedman, O.D., Roslyn, N.Y.
Until recently, the best advice I had to offer my diabetic patients who presented with sudden refractive changes or lenticular opacities was for them to return immediately to their internists to check their blood glucose and insulin levels.
While I still give this advice, I also rely on a simple nutritional strategy that's based on sound clinical and investigational data. This strategy may prevent and even reverse the pathological changes of diabetes. This month, you'll learn more about this novel nutritional approach, but first, let's look at the mechanism of diabetic cataracts.
Sorbitol in the system
Evidence has shown that sugar cataract formation and refractive power changes result from unusually high intracellular levels of the sugar alcohol (polyol) sorbitol.
Extra glucose in the hyperglycemic state causes an accumulation of sorbitol via enzymatic conversion by aldose reductase, which disturbs the osmotic balance of the lens and plays a key role in cataract formation.
Simply stated, once sorbitol is in the lens, it can't escape. It draws water into the cells and leads to swelling, and structural and chemical changes. This process may influence the refractive power of the lens, resulting in transient increases in myopia or in the visual consequences of cataracts because of the osmotic swelling of cortical fibers.
- The role of free radicals. Increased lens sorbitol levels not only exert a direct cataractous insult through their osmotic effects, but may also lead to free radical-induced opacification of lens fibers.
- The role of hydrogen peroxide. Hydrogen peroxide is generated in the formation of sorbitol. In the presence of iron, it can break down into water with the production of the highly destructive hydroxyl free radical (fenton reaction).
Hydroxyl radicals accelerate damage to the cell membrane of lens fibers resulting from sorbitol accumulation and may play an important role in the early stage of sugar cataract formation. for more information, see
right "Diabetic Retinopathy -- the Sorbitol Connection".
Diabetic Retinopathy -- the Sorbitol Connection
Retinal capillaries are composed of pericytes (mural cells) and endothelial cells. Pericytes regulate the growth of retinal capillary cells, and their loss initiates endothelial cell proliferation, which leads to the formation of
microaneurysms. Microaneurysm formation is followed by intraretinal hemorrhages, increased hypoxia and eventually, proliferative retinopathy.
It's now generally accepted that the selective degeneration of these pericytes is the hallmark of retinal vasculopathy of diabetes. Pericyte degeneration has been directly linked to sorbitol formation and is particularly vulnerable because of its high aldose reductase content; endothelial cells have none. In prevention studies with aldose reductase inhibitors, the importance of sugar alcohol formation for both pericyte degeneration and the subsequent development of retinal capillary changes has been shown to reduce the onset of early capillary changes in a dose-dependent manner.
A new approach
Aldose reductase inhibition (ARI) is a therapeutic strategy that's proposed to prevent or ameliorate long-term diabetic complications including sugar cataracts and retinopathy.
Studies have indicated that inhibition of lens aldose reductase may represent a treatment modality for the restoration and repair of lens physiology despite the persistence of diabetes or hyperglycemia.
Although a few synthetic inhibitors of this enzyme are highly effective, such as sorbinil, most cause too many side effects to be useful. However, research has discovered several natural and safe alternatives, including flavonoids (particularly quercetin and hesperidin), alpha-lipoic acid and vitamin C.
- Flavonoids. A class of polyphenolic compounds widely distributed in the plant kingdom, flavonoids are thought to promote optimal health, partly via their antioxidant effects in protecting cellular components against free radicals and partly through
Animal and in vitro testing of flavonoids have proven them to be a powerful ARI, impeding the course of cataract formation. Unfortunately, most human evidence is anecdotal, with placebo-controlled studies not yet initiated.
Flavonoids are considered safe when taken in the recommended dose -- 400 mg
- Quercetin appears in many foods, including onions, apples and tea. One recent study concludes that quercetin may cause cellular DNA damage if consumed in high amounts.
However, dozens of test-tube studies have shown that it's an anti-carcinogen against many types of cancer cells.
- Hesperidin is a natural constituent of oranges and lemons but is usually commercially derived from the Chinese bitter orange. No toxicity has been reported with
- Alpha-lipoic acid (ALA). This antioxidant is also under scientific scrutiny for potential ARI properties. It's particularly useful in treating diabetes because of its hypoglycemic activity as well as its ability to reduce the symptoms of diabetic neuropathy (a frequent complication of diabetes caused by nerve damage from elevated glucose levels).
ALA can also regenerate other antioxidants, such as vitamins C and E, and can raise intracellular glutathione levels, the depletion of which is implicated in the etiology of virtually all cataract cases. The usual dose for ALA is 200 mg
- Vitamin C. Another good ARI. In human studies, vitamin C has been found to normalize accumulations of sorbitol in red blood cells in 30 days. While red blood cells aren't the same as the lens of the eye, these results are nonetheless promising. The usual recommended dose for this purpose is 500 mg t.i.d.
Reaping the benefits
Phytochemicals, or plant-derived natural agents, are assuming an ever-increasing role in the management of many illnesses. Arming ourselves with this knowledge can have significant implications on the general and ocular health of our patients.
The most gratifying aspect of my role as a healthcare professional is the meaningful impact I've had on the health of my patients. I recently examined a 60-year-old woman who presented with type II diabetes and sight-altering lenticular opacities.
After suggesting that her condition was amenable to nutritional intervention, she began a vitamin regimen similar to the one outlined above. Her sight improved and so did her peripheral neuropathy.
This is a good example of the positive results you can achieve through adjunctive nutritional therapy.
Dr. Freedman is a nutritionally oriented optometrist. He was instrumental in developing the first antioxidant for ocular use and is a recognized expert in ocular nutrition. Dr. Freedman currently acts as a consultant to the nutrition and pharmaceutical industries.
Optometric Management, Issue: June 2001