It’s the most promising of the antioxidants we can
take to preserve and protect our vision
By Will Block
magine that you’re planning a solo trip around the world, to last several years. It’s the 1820s, so there are no cars or planes, and hardly any trains. The telegraph has yet to be invented, and there aren’t even any cell phones! (How did those people survive?) Making reservations is . . . well, you don’t make reservations. You just show up somewhere and hope for the best. You have a few friends here and there whom you can visit, but mostly you’ll be constantly on the move—alone.
James Holman (1786-1857)
But you’re plucky—with your native smarts, you figure you can go anywhere and do anything if you just put your mind to it. Of course, you don’t speak any foreign languages, you have little money, and you suffer intermittently from crippling bouts of pain from a chronic illness—but hey, obstacles are there to be overcome, right?
Speaking of which, there’s one more thing: you’re totally, permanently blind. Guide dogs haven’t been invented yet either. Your only traveling companion will be a tall stick. So off you go!
I know what you’re thinking—but the story is true! James Holman, an English naval officer who enlisted at 12 and was struck blind at 25, not only traveled the length and breadth of the world on foot and horseback, sightless and solitary, but he also had adventures that few even dream of, let alone fulfill. The story of “The Blind Traveler,” as he was known, is enthralling. It’s a tale of stupendous courage and resourcefulness, of a human spirit so indomitable that . . . well, read the book (
A Sense of the World by Jason Roberts; HarperCollins, 2006) and marvel that we belong to the same species as James Holman.
Our Eyes Are Vulnerable to Cataracts
A cause was never found for Holman’s blindness. Even today, many cases of blindness are idiopathic (of unknown origin). Among the diseases known to cause blindness, the most common is cataract, an insidious condition that degrades the lens and clouds our vision. It’s by far the primary cause of blindness worldwide, but it rarely leads to that in the more advanced countries, where corrective surgery is readily available and affordable. In the United States, for example, the leading causes of blindness are age-related macular degeneration, glaucoma, and diabetic retinopathy.
From the prevalence of cataracts, it would appear that our eyes are increasingly vulnerable to damage as we grow older. Indeed they are, but it’s not for Mother Nature’s lack of trying to protect them from harm. Because they’re so vital to us, our eyes have evolved to contain an arsenal of defensive weapons, most of which are geared to counteract the damaging effects of oxidative stress, the principal culprit in cataract formation.
Antioxidants Are Key . . .
To defend against free radicals and other reactive oxygen species, we need antioxidants. Some are native to the body, whereas others must be ingested as food or supplements. Chief among the former is glutathione, our most important and abundant antioxidant. It’s found in the lens, where it protects against oxidative degradation not only of the principal structural proteins, called crystallins, but also of certain proteins that act as ion transporters in the cell membranes. Also important are certain antioxidant enzymes, namely, catalase, glutathione peroxidase, and superoxide dismutase.
Antioxidants that we must ingest include vitamin E, a lipid-soluble compound that accumulates in cell membranes, where it helps protect against lipid peroxidation, a process that degrades and weakens the membranes. Also necessary is vitamin C, a water-soluble compound that accumulates in the cytoplasm, the cells’ aqueous interior. Vitamin C is so important for ocular health that its concentration in the eyes is about 25 times higher than in the blood.
. . . But Their Levels Decline with Age
Obviously, though, the antioxidant protections mentioned above are not sufficient to protect us indefinitely. Perhaps it’s because we’re living so much longer than nature “intended.” To put it more scientifically, we are far outliving the evolutionary adaptations of our species. Only a century ago, the average life expectancy of a newborn child was 47 years (and that was in the USA, not the world as a whole). During such a brief lifespan, the levels of glutathione and the antioxidant enzymes may remain high enough to ensure reasonably good ocular health—not to mention the health of the rest of the body. With advancing age, however, these levels decline, as do those of many other vital substances.
To help prevent cataracts, therefore, it becomes ever more important to find effective nutritional means—all the more so because surgery, although highly successful, is costly, inconvenient, and not without some risk of complications. Prevention is always preferable to therapy in any case.
Carnosine Is Helpful Against Cataracts . . .
A group of researchers in New Zealand has published a review paper on the medical (as opposed to surgical) treatments for cataracts, with a focus on nutritional supplements rather than prescription drugs. They pointed out that various drugs are currently available for this purpose, but “all are without adequate proof of efficacy.” Unfortunately, the same can be said of the supplements that have been tried for cataracts—but a lack of adequate proof of efficacy does not mean there is a lack of evidence of efficacy, even if the evidence is still preliminary and unconfirmed.
Currently the most promising supplement, in the authors’ opinion, is N-acetylcarnosine, a derivative of the natural dipeptide carnosine (from the Latin carō, carn-, flesh), which is found mainly in the heart and skeletal muscles and the brain. Research conducted in Russia has indicated that carnosine is helpful in both preventing and treating cataracts. It can be administered topically to the eye, but with poor bioavailability: because of its low solubility in lipids, it does not penetrate readily into the lens, where it’s needed.
Normal lens and lens with cataract.
. . . And So Is Its Derivative N-Acetylcarnosine
That’s where N-acetylcarnosine (NAC) is helpful—it’s more lipid-soluble (it’s also water-soluble) and thus more effective in this regard, acting as a “delivery vehicle” for the parent compound. Like carnosine, NAC occurs naturally in the body, and it too is believed to be effective in preventing and treating cataracts when applied topically. It has been shown to improve vision by partially reversing the development of the cataract, thus increasing the lens’s transmissivity to light and allowing improved vision.
NAC acts both as an antioxidant (particularly against lipid peroxidation) and as an antagonist of glycation, the harmful process that results in advanced glycation endproducts (AGEs); these are sugar-protein complexes that degrade cellular functions in many of the body’s organs and tissues, including our lenses.
What Causes Cataracts?
Cataracts sneak up on you when you’re not, uh, looking. Some people have a genetic predisposition to this disease. A few other risk factors, notably aging, are also inflexible. Most, however, can be mitigated or avoided. Among the major causes of cataracts are:
How to get cataracts (and a lot more).
- Aging – About 20% of all people over 60 have at least the beginning of a cataract in one or both eyes, and that figure rises to 80% for people over 75. As the population itself ages, the already huge numbers of cataract victims will increase.
- Antioxidant malnutrition – Inadequate intake of antioxidants, particularly N-acetylcarnosine, vitamin E, and carotenoids, is believed to facilitate the damage done to lenses by oxidative stress.
- Solar radiation – Ultraviolet radiation can damage our lenses as well as cause sunburn and skin cancer. The radiation damage from all the time we spend outdoors without sunglasses is cumulative.
- Diabetes – This pernicious disease damages many organs and tissues, including the eyes—it’s a leading cause of blindness. It’s easily preventable in most cases—just avoid obesity.
- Drugs – Also a major risk factor is the long-term use of some drugs, most notably the corticosteroids (aka glucocorticoids), powerful anti-inflammatory agents whose undesirable side effects include cataracts.
- Smoking – Is there any part of the body that smoking doesn’t harm?
- Severe dehydration – This is a common result of cholera-related diarrhea or poor nutrition in the Third World, where the rate of cataracts is high and surgical intervention is sparse.
- Heredity – Not much you can do about this one.
- Unknown – That’s right—cataracts can “just happen” for no apparent reason.
NAC Produces Impressive Results
The New Zealand authors described the one human clinical trial that has been conducted with NAC thus far—a 24-month Russian study involving 49 elderly patients and a total of 76 cataract-afflicted eyes.* Using a 1% aqueous NAC solution (2 drops twice daily), the researchers found substantial improvements in visual acuity, glare sensitivity, and lens transmissivity after 6 months, and these improvements were sustained for the duration. The controls’ untreated eyes showed significant deterioration during the same period.
The New Zealand authors acknowledged that these results were impressive, but they also pointed to the study’s numerous shortcomings and suggested that an independent study of higher quality is needed to validate the results. They also mentioned the “interesting basic physiology” underlying the use of NAC as an anticataract agent. We have previously reported on some of these aspects of NAC function. (See
“Fighting Cataracts with N-Acetylcarnosine” and
“Clear Eyes with N-Acetylcarnosine” in the April 2006 and December 2006 issues, respectively.)
Vitamin E Yields Mixed Results, with New Support
Also mentioned by the New Zealand authors as being potentially useful against cataracts were multivitamin supplements, particularly vitamins E and C, which were found, in two human population studies, to correlate inversely with risk for the disease: higher levels of these vitamins meant a lower risk, and lower levels meant a higher risk.
Unfortunately, however, these promising results were not confirmed in three large clinical trials in which the subjects took supplemental antioxidant vitamins. In two of the studies, the vitamins were found to have no effect on the development or progression of the disease; in the third, there was a small positive effect in one group of patients (in the USA) but not in the other (in the UK).
Since the publication of the New Zealanders’ review, a very large population study has been published by Harvard researchers, with positive results for vitamin E (but not for vitamin C). The subjects were 35,551 female health professionals in the United States, whose dietary habits and ocular health were followed for an average of 10 years. Over that period, the risk for cataracts was reduced by 14% in the highest quintile (highest 20%) of daily vitamin E intake from food and supplements.
Lutein and Zeaxanthin Are Beneficial
The researchers found, furthermore, that the risk for cataracts was reduced by 18% in the highest quintile of daily intake of the carotenoids lutein and zeaxanthin. These compounds, which are found in many fruits and vegetables, are vital constituents of the human retina and exist in high concentrations in the macula, the spot on the retina that’s responsible for our acute central vision. Lutein and zeaxanthin have been found in other studies to be especially beneficial for age-related macular degeneration. (See “Carotenoids Can Help Maintain Healthy Eyes” and
“Protect and Improve Your Vision with Carotenoids” in the November 2002 and March 2003 issues, respectively.)
Try to Imagine . . .
Although it seems self-evident, we should never take our precious vision for granted. While rightly concerning ourselves with the health of our heart, blood vessels, brain, stomach, joints, skin, etc., we should not overlook the organs through which we obtain about 80% of all our daily sensory input: our eyes. To gain a fuller appreciation of what that means, just close your eyes, pretend they will never open again, and try to imagine that you will do what James Holman did.
- Toh TY, Morton J, Coxon J, Elder MJ. Medical treatment of cataract. Clin Exp Ophthalmol 2007;35:664-71.
- Babizhayev MA, Deyev AI, Yermakova VN, Semiletov YA, Davydova NG, Kurysheva NI, Zhukotskii AV, Goldman IM. N-Acetylcarnosine, a natural histidine-containing dipeptide, as a potent ophthalmic drug in treatment of human cataracts. Peptides 2001;22:979-94.
- Babizhayev MA, Deyev AI, Yermakova VN, Semiletov YA, Davydova NG, Doroshenko VS, Zhukotskii AV, Goldman IM. Efficacy of N-acetylcarnosine in the treatment of cataracts. Drugs R D 2002;3:87-103.
- Christen WG, Liu S, Glynn RJ, Gaziano JM, Buring JE. Dietary carotenoids, vitamins C and E, and risk of cataract in women: a prospective study. Arch Ophthalmol 2008;126:102-9.
Will Block is the publisher and editorial director of Life Enhancement magazine.