I visit my optometrist annually for a checkup, and several years ago she started recommending that I eat more fatty fish. She told me that I had dry eyes and that the glands that produce eye lubrication on the lid were clogging up – it’s called Meibomian Gland Dysfunction which is a common cause of dry eye. While for years I just assumed I wasn’t changing my contact lenses frequently enough, now I had a diagnosis and seemingly something I could do about it. Eating fatty fish twice weekly, in combination with warm compresses on my eyes periodically, might help relieve my symptoms and potential prevent longer-term damage. While the optometrist didn’t recommend fish oil supplements, she cited the omega-3 fatty acids in fatty fish as likely beneficial for this condition. So I added this to the list of possible benefits from substituting fish for meat, and try to eat salmon at least once per week.
Now it turns out that that there’s one less reason to take fish oil supplements. A recent review has found that the supplements don’t appear to help dry eye conditions at all. So while there’s likely some health benefits from eating fatty fish, treating dry eyes isn’t one of them.
Dry eyes and fish oil
Fish oil supplement sales are big business, and the category is one of the more popular among supplements. Annual sales of fish-derived supplements amount to more than a $1-billion market in the United States, driven more by hype than good evidence. Many formulations are sold over-the-counter, while others require a prescription or are available for purchase from a health care provider (see, for example, Jann’s post on the prescription fish oil, Vascepa). The enthusiasm has been driven in part by observational studies of diets, noting a relationship between fatty fish consumption and cardiovascular disease. But in trials with fish oil capsules, those benefits haven’t been proven.
Dry eye is a very common condition (affecting about 14% of American adults) that can distort vision and affect quality of life. It’s a consequence of the dysfunction of tear-secreting glands, and can be made worse by medications and environmental conditions such as heating, drafts, and air conditioning. Allergens can worse dry eyes, but don’t cause it. In most cases, the condition isn’t serious, just bothersome – usually blurred vision and irritated eyes. Severe forms can cause scarring of the cornea and even ulceration. The condition isn’t considered curable, and treatment focuses on addressing symptoms. Usual treatments include eye drops (“artificial tears”), lid scrubbing, and frequently, omega-3 fatty acid supplements. There doesn’t seem to be clear evidence to suggest why omega-3 fatty acids would help dry eyes, beyond the thought that there might be some sort of anti-inflammatory effect. So a trial was developed to actually test the hypothesis.
The paper is entitled “n−3 Fatty Acid Supplementation for the Treatment of Dry Eye Disease” and comes from the Dry Eye Assessment and Management Study Research Group, published in April in the New England Journal of Medicine. The study was funded by the National Eye Institute of the National Institutes of Health. (Thank you, America, for funding this study.)
This was a really well-designed study that is “generalizable” meaning that the results should be relevant for many people. This study took place at 27 centres and enrolled 535 community-dwelling people with a minimum 6-month history of moderate to severe dry eyes, as evaluated by the Ocular Surface Disease Index (ODSI). Patients were excluded if they couldn’t comply with the 5-day run-in of supplements, if they wore contact lenses recently, or if they had other ocular conditions recently. Participants were randomly assigned to a 3,000mg daily dose of fish-derived fatty acids, or to an olive oil placebo. Interestingly, patients could continue using treatments for dry eye, including fatty acid supplements, as long as the daily dose was below 1,200mg. This makes the findings even more interesting.
349 patients were randomized to the treatment arm, taking five capsules of fish oil per day, providing a total of 2,000 mg eicosapentaenoic acid (EPA) and 1000 mg docosahexaenoic acid (DHA). This dose of omega-3 is the highest ever tested for treating dry eye disease. 186 people received the placebo, which was 5 grams daily of olive oil (about 1 teaspoon) in identical capsules. Both patients and investigators were blinded to the treatment arm. There were no significant differences between the groups. Participants were followed for 12 months, and evaluated at the 6- and 12-month point. At 12 months, both groups were highly compliant with therapy (83%) taking five capsules daily. The primary endpoint measured in the trial was the change from the initial ODSI scale, as well as other signs of dry eye disease.
The results were not impressive. All Table 2 tells you is that there’s really no meaningful difference in terms of symptoms, despite significantly higher levels of EPA and DHA in the active treatment arm:
After 12 months, both groups improved significantly, but there was no meaningful difference between the fish oil group and the group that received a placebo. There was also no improvement in measures of dry eye that were conducted using standardized testing – so not only was there no subjective difference with the fish oil, there was no objective improvement, either. Finally, there were no significant differences between adverse events. Some may call this a “powerful placebo” but what this really tells us is that randomized trials, not anecdotes, are necessary to determine if something is actually “working”.
Don’t count on fish oils to help dry eye
This well conducted, high quality trial shows that there is no compelling reason to take fish oil supplements if you have moderate to severe dry eye. Fish oil supplements are no more effective than an equivalent placebo.