Researchers are claiming that taking supplements of a pigment found in food like spinach and eggs could sharpen vision. Douglas Heingartner looks at the evidence.

Eyesight is an easy thing to take for granted, but our ability to see is one of the human body’s most incredible senses. And there’s a lot more to it than simply discerning objects in the distance. Our eyes are capable of dealing with huge variations in contrast, for example.

One of the things that maintains healthy eyesight are pigments called macular carotenoids – like those that help make carrots orange or help create the colour in purple broccoli. These carotenoids, which can turn into a form of vitamin A, are thought to shield the retina from the damage caused by too much exposure to blue light, particularly the light emitted by the Sun.

In the past few years, researchers have found evidence that taking dietary supplements of these pigments could help to reduce glare and improve many other aspects of visual performance: sharper colours, enhanced contrast, faster recovery time, quicker visual processing speeds, and even the ability to see further.

This does not mean these supplements can replace eyeglasses in all people with refractive errors, such as near-sightedness. But could taking a daily pill really help improve our vision?

More than 600 carotenoids exist in nature, and they produce the many colours we see in fruits and vegetables. We cannot create them ourselves, so we metabolise them from our diet.

Carotenoid supplements have long been successfully used to treat a form of vision loss known as age-related macular degeneration (AMD) – it damages the macular region at the back of the retina and is currently the leading cause of blindness in the developed world.

Yet in the past few years, researchers have stepped up their investigations into whether these supplements might be able to improve vision in people who already have good eyesight.

Boosting vision

A 2013 study of 150 healthy people showed that higher levels of macular pigment in the eye lessened the effects of glare, and led to quicker recovery time after exposure to bright light. Another study involving 120 healthy drivers showed that supplementation with macular carotenoids improved contrast and glare sensitivity, and lutein supplements – a type of carotenoid found in the eye – have also been found to lead to better contrast sensitivity in healthy people who spend long hours in front of a computer.

“We can get about 15-20% improved visual function in the healthy eye, which is remarkable really,” says John Nolan, a professor at the Waterford Institute of Technology in Ireland who is running an ongoing study exploring vision enhancement with these supplements. Improvements of about 30% can be achieved in patients with macular degeneration, he says. It takes about six to 12 months for the supplements to take their full effect.

Intriguing connections

Nolan refers to these carotenoids as “sunscreen for the eye” because they form a dense yellow filter in the centre of the retina, which shields it from blue light.

“It's not complicated,” says Nolan, who has published more than 60 papers on macular carotenoids. “We have a pigment in the eye. It's yellow, we get it from nutrients, and you can change it, you can increase it. And we know that by increasing it, you filter more of the blue light, and you get better visual performance.”

He argues carotenoid supplements could be particularly helpful as we get older. “We are all living longer, and we certainly do not consume enough of these particular nutrients. I believe that we're all walking around with sub-optimal visual performance,” he says.

If this is the case, could you see effects by simply changing your diet? You can get carotenoids without supplements; vegetables, corn, oranges, and eggs also contain them. But about 20 mg of carotenoids daily are needed to achieve the visual benefits described above, claim the researchers, which can be difficult to pull off even in a health-conscious diet.

“As far as vision goes,” says Billy Hammond of the University of Georgia, “we’re all sort of in a deficient state. We have very low levels of these things within our eye that we once had very high levels of. It is actually pretty challenging these days to have a healthy diet, so supplements likely do have a role to play.” 

Other researchers have been experimenting with carotenoid-enhanced eggs instead. The pigment is more “bioavailable” to humans in this form – that is, it’s easier for us to absorb – and also more palatable to consumers who don’t want to take more pills.

Brain improvements

There is also some evidence linking carotenoids with other processes in the body: in motor skills, hearing, immune responses, and cognition.

Nolan published a paper in July indicating that Alzheimer’s patients are highly deficient in their levels of macular pigment, in addition to having worse vision. And a 2013 study by Hammond found that higher macular pigment levels are associated with faster processing speed and better balance (measured by how long you can stand on one foot with both eyes closed).

While these associations do not necessarily mean that supplements can help, a few studies have suggested possible cognitive benefits from taking the pigment. A study Hammond co-authored in September found that macular carotenoid supplements lead to improvements in the brain’s visual processing speed in young people. And other recent research has shown that lutein supplementation leads to improved cognitive skills in older people.

Macular pigment “affects biology profoundly, not just in terms of preventing dementia and macular denegation, but also in how the brain functions overall,” claims Hammond. It’s worth pointing out, however, that most of the studies so far have identified only correlations between the pigments and brain function – the mechanism is not yet clear.

So, while it may be early to say that we should all embrace carotenoid supplements, the accumulating body of research about their benefits suggests that our diet may influence the health of eyes and brain more than we once thought.

If you would like to comment on this, or anything else you have seen on Future, head over to our Facebook or Google+ page, or message us on Twitter.

Disclaimer
All content within this column is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. The BBC is not responsible or liable for any diagnosis made by a user based on the content of this site. The BBC is not liable for the contents of any external internet sites listed, nor does it endorse any commercial product or service mentioned or advised on any of the sites. Always consult your own GP if you're in any way concerned about your health.