Vitamin A, nutrition and what food can actually do for your eyes

Nutrition and eyesight is a field with one very solid, very serious finding and a great deal of marketing built on top of it. The two are worth separating.

The solid finding

Vitamin A deficiency causes blindness, and it remains a real public health problem in parts of Nigeria, particularly among young children and pregnant women.

The sequence is well described. Vitamin A is required to make rhodopsin, the pigment that allows the retina to work in low light, so the earliest sign is difficulty seeing at dusk — night blindness. As deficiency deepens, the conjunctiva dries and develops the foamy white patches known as Bitot's spots. Then the cornea itself dries, ulcerates, and in severe cases softens and perforates. That final stage, keratomalacia, can destroy an eye within days, and it typically strikes a malnourished child during an episode of measles or diarrhoeal illness.

It is entirely preventable, and treatment with vitamin A at the early stages reverses it. This is why vitamin A supplementation programmes for children exist and why they matter.

Sources are widely available here: red palm oil is exceptionally rich in carotenoids, as are carrots, sweet potato, pumpkin, mango, pawpaw, and dark leafy greens such as ugu, ewedu and bitterleaf. Liver, eggs and dairy provide the preformed vitamin.

The limit of that finding

If you are not deficient, more vitamin A does not improve your eyesight. It does not sharpen vision, it does not reduce your prescription, and it does not prevent short-sightedness. The carrot story that most people grew up with was wartime misdirection — a cover story for radar — and it has proved remarkably durable.

Excess preformed vitamin A is actively harmful: it accumulates, and high intakes are toxic to the liver and hazardous in pregnancy. This is a nutrient to obtain from food rather than to take enthusiastically in supplement form.

What else has reasonable evidence

For age-related macular degeneration specifically, there is good trial evidence that a particular combination of antioxidants and zinc slows progression in people who already have intermediate or advanced disease in one eye. This is a specific formulation for a specific group, prescribed after diagnosis. It does not prevent macular degeneration in people who do not have it, and it does nothing for any other eye condition.

Lutein and zeaxanthin, concentrated in the macula and found in dark leafy greens, maize and egg yolk, are plausibly protective and are part of the formulation above. The evidence for supplementing in an otherwise healthy person is weak.

Omega-3 fatty acids have been studied extensively for dry eye, with mixed results — earlier positive findings were not confirmed by a large, well-conducted trial. Oily fish is good for you for other reasons.

A diet that controls blood sugar and blood pressure is, by a wide margin, the most effective nutritional intervention for your eyes. Diabetic retinopathy and hypertensive retinal disease are among the leading causes of sight loss in working-age adults, and both are substantially diet-responsive. This is far less marketable than a capsule, and far more effective.

What has essentially no evidence

Supplements marketed for "eye strain", for reducing your spectacle prescription, for reversing cataract, or for improving night vision in people who are not vitamin A deficient. Eye drops sold to dissolve cataract. Any product promising to eliminate the need for spectacles.

The sensible position

Eat a varied diet with plenty of dark green and orange vegetables — which in Nigeria is both achievable and inexpensive. Ensure children in particular are getting vitamin A, and take up supplementation programmes where they are offered. Control blood sugar and blood pressure. Do not smoke, which is worth more to your macula than any supplement.

And have your eyes examined, which no diet substitutes for.