Breastfed infants appear to have numerous advantages over their formula-fed counterparts, especially in the area of visual development. Some studies have suggested that the omega-3 fatty acid docosahexaenoic acid (DHA), which is found in mother's milk and which is present in the retina and in the brain, may be important in this regard. Accordingly, infant formula manufacturers began fortifying some of their products with DHA, along with another fatty acid, arachidonic acid (ARA), several years ago. One group involved in this research published a study (Am J Clin Nutr 2005;81:871-9) showing that infants consuming such a fortified formula had better visual acuity from 6 through 52 weeks of age than infants consuming formula without DHA. These researchers also measured stereoacuity, which is a determination of how well one can see in three dimensions (a kind of depth perception). They found that the infants receiving the DHA-supplemented formula had better stereoacuity than the other group at 17 weeks of age but not later on.
Now a new, prospective study has appeared comparing the stereoacuity of breast-fed infants with those who had received either DHA-supplemented formula or formula without DHA for the first six months of their lives (Am J Clin Nutr 2007;85:152-9). At 4 to 6 years of age, the breastfed children were much more likely to have achieved a high level of stereoacuity than the children who had been given formula as infants. Those who had received the DHA-containing formula fared no better than those receiving the other formula. Although DHA may confer some benefits, this report strongly suggests that components of mother's milk not found in any infant formula are responsible for the visual advantage enjoyed by the breastfed children in this study. The implication is that formula, even if supplemented with DHA and ARA, is a poor second choice to mother's milk.
In June, 2006, the U.S. Food and Drug Administration (FDA) approved a new treatment for the wet form of macular degeneration that may prove to be a shot in the arm for the disease, although "shot in the eye" may be more accurate. Most macular degeneration involves a "dry" kind of degeneration of the central retina, but the "wet" form produces the most precipitous and most severe loss of vision. The latter is called "wet" because a network of abnormal blood vessels grows behind the retina, where it can leak and bleed and play havoc with vision.
As discussed in The Eye Care Sourcebook, we are learning how to reduce the risk of visual loss in a preventive way. Increasing one's zinc intake helps. Whether adding antioxidant vitamins to the zinc results in additional benefit remains controversial. Dark, leafy green vegetables like kale, collards, and spinach may also help. Smokers should quit. Those who are overweight should eat less and lose the excess weight. Once leakage from wet macular degeneration has developed, however, other treatments come into play. Laser treatments can obliterate the abnormal vessels while creating a scar in the process. Laser therapy is mainly of benefit when the vessels are not located beneath the fovea, the very center of the macula. Photodynamic therapy, also described in my book, utilizes a photosensitizing compound called verteporfin, which is injected intravenously. When light of the correct wavelength is then directed at the retina, oxidation reactions occur and abnormal blood vessels can shut down. This technique has shown some benefit although not as much as we would like to see.
Recently, attempts have been made to find ways of inhibiting a natural substance called vascular endothelial growth factor (VEGF), which promotes the growth and leakage of the abnormal blood vessels in wet macular degeneration. The first of these to be approved, pegaptanib (Macugen), does indeed inhibit the action of VEGF and has been modestly successful in terms of reducing loss of vision.
Now the FDA has approved ranibizumab (Lucentis), another VEGF inhibitor in the form of an antibody fragment derived from bevacizumab (Avastin), a full-length antibody now used to treat cancer of the colon and rectum. Like Macugen, Lucentis is injected into the vitreous cavity of the eye. But the results with Lucentis appear to be superior, with over a third of patients actually gaining some vision. The problem is that, whereas the growth and leakage of the blood vessels are halted, the vessels are not destroyed and always have the potential to leak and bleed again. Therefore, repeat injections must be administered as often as monthly for maximum benefit. Further, injections into the eye are not with adverse consequences. Pain is common, and sight-threatening infection within the eye, inflammation, bleeding, elevated pressure, and damage to the lens resulting in cataract formation can all occur. The drug is also quite expensive, to the tune of almost $2,000 per injection. Finally, the effect on the eye years down the line is unknown.
Hopefully, new and better treatments for macular degeneration will soon emerge. But, as always, prevention remains the highest form of healing.
Dry Eye Syndrome is an extremely common condition, accounting for a large percentage of the complaints for which people seek care from an ophthalmologist. People have long wondered whether diet plays a role. Now we have evidence that it does. A report from the Women's Health Study, a prospective study of almost 40,000 female health professionals, indicates that higher intake of omega-3 fatty acids, as from fish, may reduce the risk. The presumed mechanism is the anti-inflammatory effect of omega-3 fatty acids. It has long been known that inflammation of the tear gland and other associated structures plays a role in the development of dry eye syndrome. In fact, eye drops containing cyclosporin, a very potent immunosuppressive drug, are now used in resistant cases. Omega-3 fatty acids tend to have an anti-inflammatory effect because they balance out the effect of arachidonic acid, an omega-6 fatty acid that comes mainly from meat. Arachidonic acid is converted by the body to inflammatory chemicals, such as the 2-series of prostaglandins, whereas omega-3 fatty acids are converted to anti-inflammatory substances, like the 3-series of prostaglandins, which oppose the action of the 2-series. This sugggests an optimal dietary approach that has thus far not been tested: a vegetarian diet. Because vegetarian diets are low in arachidonic acid, they may result in less of an inflammatory tendency in the body. As a result, there would be no need to increase omega-3 fatty acid intake. Hopefully, future studies will shed light on the matter.
The harnessing of fire as a tool by humans led to the cooking of food, which stands in contradistinction to the eating habits of the rest of the animal kingdom. Cooking destroys disease-producing organisms (usually a consequence of animal agriculture), but are there any adverse effects on health? "Raw foods" diets are trendy, but the arguments in favor of such diets by their advocates are often unscientific. Nevertheless, a growing body of evidence indicates that cooking foods more lightly or not at all may be beneficial to health.
First, cooking destroys nutrients, especially vitamin C and some of the B-vitamins. Second, cooking can produce carcinogens (cancer-causing chemicals): grilling of meat is a frequently cited example. Third, crushing (as with eating) or cutting certain foods can activate beneficial enzymes (proteins that catalyze chemical reactions) in uncooked but not in cooked foods (Cancer Epidemiol Biomarkers Prev 2004;13:1422-35). For example, activation of the enzyme allinase in garlic converts alliin to allicin, a phytochemical that may have anticarcinogenic (cancer preventive) properties. Similarly, activation of the myrosinase enzyme in cruciferous vegetables causes the formation of compounds that induce the production of the liver's phase 2 enzymes that inhibit carcinogenesis and that may help prevent chronic diseases. Finally, cooking (especially at high temperatures and for long periods) causes the formation of advanced glycoxidation end products (AGEs)(J Am Diet Assoc 2004;104:1287-91), which are felt to promote aging and diabetic complications.
Although few of us are willing to give up cooked foods entirely, increasing the percentage of food consumed in the raw state and cooking foods as lightly as possible, e.g., avoiding toasting of bread and browning of other foods, would seem prudent.
Studies are showing that being overweight increases your risk of many chronic diseases, including cancer. A new study published in the June 2003 issue of the journal Archives of Ophthalmology shows that we can probably include age-related macular degeneration, the most common cause of poor vision in the elderly, among those diseases. Being obese or having a large waist size more than doubled the risk as compared with people of average weight or waist size. It is not entirely clear whether the obesity itself or the fact that obese people tend to eat more than others is the culprit. A growing body of evidence is showing that how much we eat is just as important as what we eat. Cutting calories can lower the risk of (or even reverse) adult-onset diabetes, lower blood pressure, lower cholesterol levels, and produce other potentially beneficial biochemical changes in the body. See "The Latest on Macular Degeneration" below for information about how the quality of the diet can affect the risk.
Keratoconus is a condition in which progressive thinning and distortion of the cornea occurs. It usually begins in young adulthood, often in people with a history of seasonal allergies. Because the irregularity of the surface of the eye produces irregular astigmatism, rigid contact lenses are usually necessary to correct the vision. Ultimately, because of progression of the keratoconus, corneal transplant surgery is required. This is very major surgery requiring about one year for complete healing, and rejection or failure of the transplanted tissue can sometimes occur even years down the road. Although the surgery has a high success rate, it would be desirable to find a way to avoid surgery.
In a study just published in the American Journal of Ophthalmology, German and Swiss researchers reported a new and promising approach. Riboflavin (vitamin B2) eye drops were applied to the eyes, which were exposed to ultraviolet light. Riboflavin is a photosensitizer, which means that it initiates a string of chemical reaction after being exposed to light. The purpose was to cause crosslinking of the collagen, the protein of which the cornea is composed. The result was that the corneas became more rigid and the keratoconus stopped progressing, thereby averting the need for surgery. No side effects were seen in the 3 month to 4 year follow-up period.
In The Eye Care Sourcebook, I discussed riboflavin as an important element of the antioxidant defense system of the eye. However, I cautioned against taking large doses because of its ability to be a photosensitizer. I was concerned that excess riboflavin in the eye might lead to free radical formation in the lens of the eye and cataract formation. But, in the present study, that did not appear to be a problem. Still, more studies with longer follow-up periods are required to ensure that harm does not ensue to the cornea or the lens in the long run.
"High-Fat-Diet Findings Stun M.D.s," screams the Arizona Daily Star. To listen to the news media, which seem to make a habit of misrepresenting nutritional studies, you would think that those dumb doctors have changed their minds once more about what to eat. The message is clear: go back to eating your cheeseburgers; it won't hurt you. Unfortunately, it is exactly this gluttonous meat-based dietary lifestyle that has led to the epidemic of obesity, heart disease, and other chronic diseases we are now facing.
At issue are the high-fat, high-protein, low-carbohydrate diets that have achieved popularity through the glut of quackish books that have promised the easy road to weight loss and presumably better health. These books have cast carbohydrate as the villain, something to be avoided at all cost, despite the fact that the trimmest, healthiest, and most long-lived populations are those who consume low-fat diets high in complex carbohydrate! Any diet that results in consumption of fewer calories will cause you to lose weight. High-fat diets may put people into a state where they don't feel like eating as much. But is that desirable? Do you want your tombstone to read, "He lost lots of weight but then he died?"
To be sure, the current high-fat diets do not seem to raise cholesterol levels as much as one might expect. That may be the result of their low caloric content, and eating less of any food is bound to yield dividends such as this. But comparing the results with those produced by the National Cholesterol Education Program's Step 1 diet is not appropriate. The latter diet limits calories from fat to no more than 30% (hardly a low-fat diet), and cholesterol to less than 300 mg a day, which is not much of a reduction. This Step 1 diet has never been shown to reverse heart disease and it is not all that much different from the standard American diet. In short, comparing high-fat, high-protein diets with the Step 1 diet is comparing one unhealthy diet with another. A low-fat vegetarian diet can achieve dramatic lowering of cholesterol levels and is the appropriate model for dietary intervention in this respect.
It is important to realize, however, that cholesterol levels are just one of the many risk factors for hardening of the arteries (atherosclerosis). The goal of physicians is to treat patients, not cholesterol levels. In any therapeutic program, the measure of success is the change in the incidence of heart disease. So regardless of the effect of high-fat diets on cholesterol levels, we have to examine some of its other effects. First, high-fat diets (40% of calories from fat) increase the coagulability of the blood, that is, its tendency for blood clot formation, by increasing levels of factor VII, one of the blood clotting factors (Arterioscler Thromb Vasc Biol 1997;17:2904-9; Br J Nutr 2001;86:207-15). A higher coagulability of the blood is felt to accelerate the process of hardening of the arteries and thereby promote heart disease. Second, a single high-fat meal also impairs arterial endothelial function (Am J Cardiol 1997;79:350-4; JAMA 1997;278:1682-6). This means that the blood vessels do not dilate when they need to. Such an impairment can cause an acute heart attack and is also felt to contribute to hardening of the arteries. Finally, cholesterol-rich diets cause a transient elevation in the bloodstream of fats that promote hardening of the arteries (Circulation 1979;60:473-85). This can occur even if cholesterol levels in the blood at other times remain "satisfactory." So here are just three reasons why high-fat diets may increase the risk of heart disease.
A claim commonly made by proponents of high-fat diets is that high carbohydrate diets raise blood levels of triacylglycerols, often referred to as triglycerides. High triglyceride levels are considered a minor risk factor for heart disease and are often especially problematic in diabetics. This claim can be easily refuted by the facts. First, not all carbohydrate has the same effect on the body. One does not have to be a nutrition scientist to understand that complex carbohydrate (starch) as contained in vegetables or whole grains is quite different from simple carbohydrate, better known as sugar. Indeed, a very nice study published in 1998 (Amer J Clin Nutr 1998;67:631-9) showed that substituting starch for sugar reduces the synthesis of triglycerides by the body dramatically. The studies showing high triglyceride levels in people consuming high-carbohydrate, low-fat diets generally employed diets high in sugar. Second, a study published in 2001 (Arterioscler Thromb Vasc Biol 2001;21:1520-5) showed that even when higher triglyceride levels result from a high-carbohydrate diet, exercise prevents the triglyceride build-up. In other words, the accumulation of triglycerides should be thought of as a couch potato phenomenon, not an obligatory part of such a diet. Finally, an excellent study published in 2000 (J Nutr 2000;130:2503-7) showed that when diabetics were fed a high-carbohydrate as opposed to a high-fat diet, the triglyceride-rich particles called VLDL in their blood were different in character from those in people consuming the latter diet. They had fewer large VLDL particles than did those on the high-fat diet. The significance is that big VLDL particles are felt to increase the risk of hardening of the arteries in diabetics. So all triglycerides are not created equal, and a higher triglyceride level does not automatically translate into a higher risk for heart disease.
The best evidence we have, and it is overwhelming, is that the ideal diet remains, as it has always been, a plant-based diet high in fiber and complex carbohydrate and moderately low in protein and fat. Such a diet might derive 70% of calories from carbohydrate, 15% from protein, and 15% from fat. Both the quantity and the quality of the food consumed are important.
LASIK is the refractive surgical procedure being performed in assembly line operations by today's entrepreneurial ophthalmologists, who seem to have no qualms despite the fact that few would have it done to themselves or to their family members. In The Eye Care Sourcebook, I warned of the possible long-term consequences. For example, dry eye syndrome, an extremely common short-term complication, may become worse as a person ages, resulting in vision and other problems. Now, another concern I discussed, the loss of keratocytes (cells within the collagen-rich stroma of the cornea), has become more worrisome as the result of recent studies.
In one study, people undergoing LASIK suffered a loss of keratocytes not only in the corneal flap created by the surgery but also in the remaining cornea immediately behind the area of tissue removal by the laser. And a new German study has shown that the number of keratocytes in the corneas of healthy people declines significantly after the age of 50.
Why is this worrisome? Keratocytes have a number of important functions, e.g., producing collagen, maintaining the transparency of the cornea, and helping the cornea repair itself. If LASIK destroys keratocytes, then what will happen to people who have had LASIK when they reach their fifties or sixties and the number of keratocytes declines further? Only time will tell.
A number of studies over the past few years have suggested that consuming foods rich in lutein, a yellow pigment in the same class as beta-carotene, may help prevent the nuclear sclerotic form of cataract. Dark, leafy green vegetables, such as spinach, collard greens, kale, mustard greens, Swiss chard, and turnip greens, are good sources of lutein. Now, a study just published in the journal Ophthalmology demonstrates that lutein may also protect you from the posterior subcapsular form of cataract, a particularly disabling type. This study also showed that high blood levels of other carotenoids, namely, alpha-carotene, beta-carotene, and lycopene, were associated with a lower risk of certain types of cataract. Carrots and pumpkins are the best sources of alpha-carotene; tomatoes, red watermelon, pink grapefruit, and guava supply lycopene; while carrots, pumpkins, squash, dark green vegetables, tomatoes, sweet potatoes, apricots, and cantaloupe are all good sources of beta-carotene. But lutein and its close relative zeaxanthin are the only carotenoids found in the lens of the eye. It is possible, then, that the other carotenoids do not prevent cataract in themselves but are only what scientists call "markers." This means that other, unknown substances found in the same foods may be the real cataract preventers. What we should learn from this is that the best preventive is consuming a good variety of vegetables and fruits rather than heading to the supplement counter of your local health food store.
Lured by its low content of saturated fatty acids, high content of monounsaturated fatty acids, and favorable 3:1 ratio of omega-6 to omega-3 fatty acids, some people have been turning to canola oil as a heart-healthy choice. But rapeseed oil, of which canola is a refined North American version, is about 40% erucic acid, a controversial monounsaturated fatty acid that some experts fear could cause heart disease. Accordingly, canola oil was approved on the condition it contain less than 5% erucic acid. All well and good. But some feel the FDA was a bit premature when it declared canola oil "generally regarded as safe" in 1985, perhaps succumbing to pressure exerted by the Canadian government and powerful multinational corporations.
Now a very legitimate concern has surfaced. Refined oils, including canola oil, are subjected to a steaming process to deodorize the oils and make them palatable to consumers. However, this process causes about 25% of the omega-3 fatty acid called alpha-linolenic acid to be converted to a trans fatty acid. You may recall that the trans fatty acids found in margarine, dairy products, and partially hydrogenated oils have been found to raise cholesterol levels and have other adverse effects on blood vessels. Now, a study just published in the British Journal of Nutrition shows that trans alpha-linolenic acid also has these negative effects on cholesterol levels.
So what to do? True, olive oil is probably the least objectionable among the oils, if not the "health food" people commonly suppose it to be. But maybe the healthiest alternative is a low fat diet without added oils. A study just published in The Journal of Nutrition, comparing low fat and high fat diets, found that although people consuming the low fat diet had a lower intake of omega-3 fatty acids than those consuming the high fat diet, they had higher absolute and relative amounts of omega-3 fatty acid in their cell membranes as did those consuming the high fat diet. The reason may be that the higher content of omega-6 fatty acids in high fat diets competes with the enzymes the omega-3 fatty acids need to elongate themselves. For those who are still uncertain about their omega-3 fatty acid needs, dark, leafy green vegetables, walnuts, flaxseeds, and soyfoods are all sources of alpha-linolenic acid, the parent omega-3 fatty acid.
Three reports on age-related macular degeneration (AMD) just appeared in the October 2001 issue of the journal Archives of Ophthalmology. In one study of almost 2600 people in the south of France, there was no evidence that sunlight exposure played a role in the development of AMD. Previous studies exploring this question have been inconsistent in their results. Therefore, although excessive sunlight exposure probably does play a role in cataract formation, we cannot say the same with regard to AMD. A second study in this issue confirmed what has long been known -- that cigarette smoking increases the risk of AMD. Possible reasons for this association include the pro-oxidant effect of cigarette smoke and the harmful effect of cigarette smoke on blood circulation. The third study looked at the effect of taking a supplement containing the antioxidants vitamin C, vitamin E, and beta-carotene, a supplement contain 80 mg of zinc, or the two combined. The patients were treated for an average of over six years. Those taking the zinc alone or the zinc combined with the antoxidants showed a slight benefit compared with those not taking zinc. There is some evidence that zinc may be beneficial in slowing down the progression of AMD but no good evidence that such large dosages need to be taken. As I pointed out in The Eye Care Sourcebook, there are a number of potentially harmful effects that could be seen from supplementing with so much zinc. The best approach is to consume a healthy plant-based diet with lots of dark, leafy green vegetables, good sources of the retinal pigment called lutein as well as vitamin E.
In a large study called the Age-Related Eye Disease Study, the effect of a supplement containing 500 mg of vitamin C, 400 I.U. of vitamin E, and 15 mg of beta-carotene was studied in almost 5,000 middle-aged to elderly people (Archives of Ophthalmology, October 2001). After an average follow-up period of over six years, there was absolutely no evidence that taking such a substance could prevent cataract. Why should these antioxidants fail to prevent cataract, a disease that is felt to be caused by the oxidation of the proteins in the eye's lens? For one thing, the forms of vitamin E and beta-carotene contained in most supplements is different from the forms present in foods. Secondly, foods contain many other antixidants besides vitamin C, vitamin E, and beta-carotene. For example, some contain lutein, a yellowish pigment related to beta-carotene that is naturally present in the lens of the eye. In addition, plant foods contains an abundance of flavonoids, which are phytochemicals with antioxidant properties. The moral of the story is: eat your fruits and vegetables, especially your dark, leafy greens, and don't worry so much about supplements.
In The Eye Care Sourcebook, I expressed some concerns about Viagra and the eye. The way Viagra carries out its effect is by inhibiting an enzyme called phosphodiesterase type 5. It turns out that there is a related enzyme in the retina of the eye called phosphodiesterase type 6. Although Viagra is only about 10% as active against this type 6 enzyme as it is against type 5, it does affect vision transiently in a small percentage of the men who take it. Blurring, increased light sensitivity, or a bluish tinge to the vision are the usual symptoms. Since people who are born with a lack of this phosphodiesterase enzyme develop a rare type of degeneration of the retina, the concern is that Viagra might have a toxic effect on the retina when taken repeatedly over a long period.
A new study was just reported in the September 2001 issue of the American Journal of Ophthalmology. The researchers gave 200 mg of Viagra, which is at least double the recommended dose, to a group of healthy young to middle-aged men. With this high dose, about half of the men reported changes in their vision. A special test called an electroretinogram was performed. This test measures how well the retina is functioning. It showed that the Viagra did indeed affect retinal function in these men, an effect which had not completely worn off five hours after the Viagra was taken.
There have been no reports to date of any permanent damage to the retina from Viagra. Whether any evidence of damage will begin to show up after a long period of time remains to be determined. It seems probable, though, that most men taking this drug will feel that the benefits outweigh the unknown long-term risk.
Being in a hospital can be dangerous to your health. An editorial in the August 25, 2001 issue of BMJ, the British Medical Journal, pointed out that 10%of hospital patients in the United Kingdom acquire a serious infection while in the hospital, resulting in an estimated 5,000 deaths per year and a cost of about 1.5 billion dollars. The bacteria causing these infections have become resistant to many antibiotics. The evidence is that many of these infections could be prevented if doctors and nurses simply washed their hands after seeing every patient. When a health care worker touches a patient, even casually, there is a high probability that bacteria will be transmitted to the hand of that health care worker, and this is how many of the infections occur. The authors recommend using an alcohol and glycerol hand rub between patients, which should take only 10 or 20 seconds.
I can attest to the widespread nature of this problem. In my ophthalmology office, I often had family practice doctors in training spend some time with me, observing and examining patients. Although I would wash my hands in between patients, rarely did I see these young doctors do so. When I mentioned the problem to the director of the family practice training program, the response I got was the equivalent of a shrug of the shoulders. Why should this be? My guess is that there is nothing glamorous about washing your hands, so how can it compete with activities like administering drugs and doing surgery?
In the section on refractive surgery in The Eye Care Sourcebook, I mentioned that if surgery was the only way we had of correcting nearsightedness and then someone invented eyeglasses so that surgery would not be necessary, this would be hailed as a tremendous medical advance. The authors of the editorial in BMJ have a similar feeling about handwashing. The potential benefit from handwashing, which costs almost nothing and takes just a few seconds, is so great that if a new drug had this beneficial effect, it would be accepted without question as a great milestone in medicine. We need to repair the health care system so that we can attract the kinds of doctors and nurses who will feel that handwashing is a sine qua non of patient care.
Return to Home Page