Friends, this is a pretty long post. But here’s the speed version:
Eating a vegetarian or vegan diet, especially with a high dietary intake of fruits, vegetables and leafy greens, is correlated with a lower incidence of cataracts.
Want to understand the details? Read on …
You may have already had cataract surgery yourself, and you certainly know someone who has. Cataract surgery is one of the most common surgeries performed in the US (and worldwide). And this is precisely why as a nation, we should be looking at factors which may delay the onset of cataracts. The National Eye Institute has projected that the prevalence of cataracts in 2010, 24.4 million people, will double to about 50 million people by 2050.1 This is an incredibly large cost for our system to bear, and delaying the onset of cataract even by a year would provide a significant cost-savings. In addition, although cataract surgery is uncomplicated in most people, this is not true for all patients. Even if 99% of cataract surgeries are free of complications, the one percent who do experience a complication can have a permanent impact on their vision. If we can decrease the need for surgery, we can decrease the number of people each year who experience complications of surgery.
The National Eye Institute, in their education for the public re: cataracts, encourages people to “eat green leafy vegetables, fruit, and other foods high in antioxidants.”1 However, the American Academy of Ophthalmology in their 2016 recommendations to ophthalmologists nationwide noted that “Dietary intake and nutritional supplements have demonstrated minimal to no effect in the prevention or treatment of cataract.”2 These two statements seem quite contradictory, so what is going on here? Is there a link between what we eat and the development of cataracts?
The group of doctors who created the Preferred Practice Pattern have a big job. They review all of the available research studies to determine what conclusions they can draw, in order to advise practicing ophthalmologists how best to help their patients. The quality of research is judged in a hierarchy. The best research is widely considered to be a randomized controlled trial. In these studies, scientists study two groups — a control group and an intervention group. They try to control the two groups’ characteristics to make it an even comparison, and they limit the differences in interventions between the two groups in order to make it clear which factors are causing a difference. For example, a randomized-controlled trial looked at beta-carotene supplements in more than 28,000 men, and found that there was no significant difference in the risk of cataract surgery over a five to eight year period in the men who were taking beta carotene vs. those who weren’t.3
Observational studies are considered to be less valuable in drawing firm conclusions. An observational study is more of a snapshot in time, in which certain trends are noted, but firm conclusions can’t be drawn. For example, the Women’s health Study looked at more than 35,000 women and noted that the more fruits and vegetables women ate, the lower their risk of cataracts. But they didn’t randomize participants to different interventions, such as educating one group of women eat 10 servings of fruits or vegetables daily for 10 years and the second group to eat their normal diets to see if this intervention affected the rate of cataracts over time.
Does this mean that observational studies aren’t valuable? I don’t think so. First, let’s think back to the scientific method you may have learned in elementary school. The first step is to observe. Observations give us valuable insights that can lead to further study to help understand if the observation is true and enduring.
Let’s take a deeper look at what the studies re: nutrition and cataracts have to tell us. At the end of the American Academy of Ophthalmology’s Preferred Practice Pattern, “Cataracts in the Adult Eye”, the authors provide a very helpful summary of the available research, which I have condensed and abbreviated here:
Nutrition and CataractsInformation Abbreviated from Appendix 3 of the Preferred Practice Pattern, "Cataract in the Adult Eye", compiled by the American Academy of Ophthalmology, 2016.
|Nutrient or Dietary Pattern||Study Type(s)|
Randomized Controlled Trial (RCT) vs. Observational Studies (Obs)
|Beta-Carotene Supplements||RCT||No effect
|Lutein/Zeaxanthin Supplements||RCT||No effect
|Multivitamin/Mineral Supplements||RCT||Mild effect, stronger effect in nutritionally deficient populations|
|Omega 3 supplements||RCT||No effect
|Riboflavin/Niacin supplements||RCT||Significant effect in a nutritionally deficient population|
|Selenium Supplements||RCT||No effect
|Vitamin C and E||RCT||No effect|
|Vitamin C, E and Beta Carotene||RCT||No effect|
|Dietary intake of antioxidants (fruits, vegetables, whole grain, coffee)||Observational||Those who ate the most antioxidants in their diet had a 12.8% decrease in incidence of cataract compared to those who ate the least.|
|Dietary Intake of Meat and Fish||Observational||High meat eaters had a higher incidence of cataract than low meat eaters, who had a higher incidence than pescatarians (fish but no meat), who had a higher incidence than vegetarians, with vegans having the lowest risk.|
|Vegetarianism||Observational||Vegetarians at lower risk of cataracts than meat eaters.|
|Fat Intake||Observational||Reduced risk of cataract extraction with higher intake of long-chain fatty acids and fish.|
|Fruit and Vegetable intake||Observational||Reduced risk of cataract associated with higher dietary intake of fruits and vegetables|
|Dietary intake of Lutein/Zeaxanthin||Observational||Modestly lower risk of cataract with higher dietary intake|
|dietary intake of Riboflavin/Niacin||Observational||No effect|
|dietary intake of Vitamin C||Observational||Reduced incidence of cataract with higher dietary intake|
|supplemental intake of Vitamin C||Observational||Two studies showed increased risk of cataract with increased supplement use, and one study showed no effect|
|Dietary or Supplemental intake of Vitamin E||Observational||No effect|
|Supplemental intake of Vitamin E||Observational||Increased risk of cataract|
From looking at these randomized controlled trials and observational studies noted here, I come up with three major takeaways:
- Nutritional supplements were not beneficial, unless the study population was nutritionally deficient.
- Higher dietary intake of fruits, vegetables and specific nutrients obtained in the diet (not in supplements) decreased the incidence of cataracts.
- Two large studies noted a correlation between meat consumption and cataract incidence: subjects who ate more meat were more likely they were to develop cataracts, and subjects who were vegetarian or ate no animal products (vegan) were least likely.
This is helpful, and allows me to say with confidence to all of my patients who are taking supplements with claims of “promotes eye health” that it is unlikely they are doing anything to prevent cataracts. In fact, some studies suggest that supplement use may increase the incidence of cataracts. It is much better to get your vitamins and antioxidants in your diet, from fruits, vegetables and leafy greens. Finally, I feel comfortable saying that there is evidence that vegetarians and vegans have a lower incidence of cataracts.
Second, I find it interesting that I was completely unaware of this data until after I adopted a whole-foods plant-based diet, which I did for personal reasons completely unrelated to my profession as an eye physician and cataract surgeon. Frankly, for me, it’s just a bonus to find out that making this change may stave off cataract surgery a little longer for me than it might have otherwise.
I know a fair number of optometrists and ophthalmologists, and have never heard any of them discuss the potential association between eating meat and incidence of cataracts. Perhaps I was distracted during our lecture on cataract epidemiology in my residency program, and I missed this pearl. It’s possible. However, I think the more likely cause is a bit more insidious. In our medical culture, suspicion and a dismissive attitude remain for many aspects of “alternative” or “complementary” medicine. Some of this is founded in genuine frustration with cases of unscientific or biased recommendations and practices, especially egregious in those cases in which it appears patients are being taken advantage of for profit. But these cases do not explain the whole of the medical establishment’s attitude. The terms vegetarian and vegan, for some, are politically loaded terms that carry a certain connotation, and these terms tend to “co-locate” with alternative, complementary or naturopathic medical disciplines. And I suspect that this correlation dissuades some researchers from pursuing this type of research for fear of being considered unscientific or “flakey”. The same effects may well translate to committees coming up with summary recommendations, educators determining the content of lectures and even practicing doctors in their day to day conversations (if they are even aware of the information). I actually don’t believe all of this is with malicious intent. Culture is a complex thing, and the more that I investigate this topic, the more I see evidence of change in the medical culture with more interest in these topics.
However, now, I cannot claim ignorance, and I have the pleasure of answering my patients’ questions a little differently when they ask if there is anything they can do to prevent cataracts. It remains true that if you live long enough, you are likely to develop cataracts. But you also have factors you have some control over, and I’ll be happy to share those with you: don’t smoke, eat your fruits and veggies, wear sunglasses, and consider eating less meat.
2 “Cataract in the Adult Eye” Preferred Practice Pattern, Ophthalmology, Volume 124 (2), pages P1-P119, February 2017
3 Teikari, J. M. , Rautalahti M., Haukka J.,et al. (1998) “Incidence of cataract operations in Finnish male smokers unaffected by alpha tocopherol or beta carotene supplements.” Journal of Epidemiology and Community Health Volume 52, pp 468-72.