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Fishing for Evidence on Omega-3s and Dry Eyes

The trendy magic bullet of omega-3 supplements is claimed to help with dry eyes, and while many human trials are favorable, there is a lot more than meets the eye

Are omega-3s the new vitamin C? In the past few years, these fats, primarily found in fish and flaxseeds, have acquired a reputation as veritable superheroes. Have arthritis? Try omega-3s! Don’t want cancer? Try omega-3s! Your car won’t start in the winter? Have you tried omega-3s?

Some websites will even direct people with dry eyes to start taking omega-3 supplements in order to help with symptoms. And while the evidence for that looked surprisingly good for a while, a recent trial casts doubt as to their usefulness in getting your eyes to stop burning.

Tears Dry on Their Own

To keep our eyes happy, a tear film is regularly produced and spread over our eyeballs when we blink. I used to think tears were just salty water but they have an unexpected degree of complexity. They’re not unlike modern, multi-layered mattresses. In the middle of the tear is a thick watery layer that washes away particles that shouldn’t be on the surface of your eye. Above that, facing outward, is a layer of oil to prevent the water from evaporating. And the layer touching the eye itself contains mucus to help the tear stick to the eye.

Either because of age, hormonal changes, the wearing of contact lenses, certain types of medications or even corneal refractive surgery like LASIK, that tear film becomes unstable. The equilibrium between all of the different components of the tear is lost. Water evaporates fast, tears become too salty, and the surface of the eye becomes inflamed. Cue the feeling of dryness, irritation, and burning.

While there is no cure for dry eyes, artificial tears can be employed but their effect is often reported as temporary and incomplete. Since omega-3s are known to be anti-inflammatory, researchers wondered if they could reduce the inflammation that accompanies dry eyes and resolve symptoms.

Inconsistent results

For a while, it really looked as if omega-3 supplements could clearly improve dry eyes, both in terms of the symptoms reported by patients and in terms of objective measurements made by doctors. A systematic review of 15 clinical trials in 2017 put a slight damper on the initial enthusiasm by showing that, while most trials showed improvement on one objective test, only a minority were positive for a second objective test, and about half of all trials reported an improvement of symptoms on the part of the participants.

The studies had issues. They tended to be small. They often only involved a single site where participants were recruited and followed up. They were short in their duration. Some were funded by the makers of omega-3 supplements. And they rarely measured participants’ intake of omega-3s before the trial began. A number of large positive trials came out of Northern India and it may be tempting to universalize them before we have read the papers. But their authors point out that the Northern Indian diet tends to be vegetarian and low in omega-3s. It’s possible that solving a deficiency in omega-3s can improve dry eyes but that giving extra omega-3s to someone who does not need them will have no effect. Vitamin deficiencies work in the same way after all.

In 2018, the New England Journal of Medicine published the results of a major, multicentre trial pitting 3,000 mg of omega-3 supplements against olive oil placebos for dry eyes. Over 500 people participated in this “real-life” trial, which sought to be less restrictive than past studies and allow participants to continue whatever treatment they were already receiving for their dry eyes. The results were clearly negative. The authors even launched themselves into 18 exploratory subgroup analyses, the kind of fishing expedition that can lead to future research, all of which came back negative. One criticism the trial got was that the olive oil capsules might not have been so inert after all. Don’t they contain molecules like oleic acid and polyphenols that are anti-inflammatory and are staples of the much-heralded Mediterranean diet? What if both the omega-3s and the olive oil improved symptoms equally? But the olive oil was refined, with low levels of polyphenols, and the Mediterranean diet contains 12 times the daily amount of olive oil these participants got. And funnily enough, sticking to the Mediterranean diet was shown in a study to increase the risk of developing dry eyes in older men!

The evidence for omega-3 supplementation to help with dry eyes has been called “inconsistent”. Early positive trials were small and very restrictive. The larger positive trials were conducted in a population likely to be deficient in omega-3s. And the biggest and most robust trial we have was unilaterally negative. The risks of supplementing with omega-3s bear mentioning. An excess could cause bleeding, one review mentions, so people with bleeding disorders should consult their doctor, and there is a controversial link between high concentrations of omega-3s in the blood and prostate cancer.

The capsules are not terribly expensive (five dollars a month) and I can sympathize with dry eye sufferers wanting to simply try them out. From an evidence-based perspective, it seems we are witnessing a common effect known as the Proteus phenomenon: early studies are small and positive, while later studies are big and negative, cutting through the noise.

Take-home message:
- Dry eyes is a condition where people report irritation and burning because their tears evaporate too quickly, which causes inflammation
- A number of small early studies reported that taking omega-3 supplements helps treat dry eyes, but the overall evidence is inconsistent and a large trial recently showed no improvement


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