Can plant pigment supplements help improve vision?
Professor Ron Douglas discusses the protective function of plant pigments called carotenoids and their effects on visual performance
Prompted by a recent episode of the BBC2 television program ‘Trust me I’m a doctor’ on the use of carotenoid supplements to boost your eyesight, around 30 people with an interest in macular pigments gathered at City, University of London towards the end of October.
At the meeting, John Barbur, Professor of Optics and Visual Science and Director of the Applied Vision Research Centre (AVOT) at City, gave a presentation outlining the science behind the TV program that prompted the meeting to be organised. In the program the presenter, Michael Mosley, took daily carotenoid supplements in tablet form for 12 weeks, while 10 volunteers drank evil looking (and tasting) vegetable smoothies. Serum levels and aspects of visual function were tested both before and after the ingestion of these high doses of carotenoids.
These carotenoid pigments – which are plant pigments responsible for bright red, yellow and orange hues in many fruits and vegetables - play a very important role in the eye. In particular, the macular pigment in the central retina through which light has to pass before being absorbed by the photoreceptors is comprised of a layer of these carotenoid pigments.
The function of such pigments, which filter out blue light, is twofold; to improve image quality (by removing the wavelengths most prone to scatter and chromatic aberration) and to protect the retina through both absorbing the wavelengths most likely to cause retinal damage and to mop up potentially damaging free radicals formed when light and oxygen interact.
While serum levels of the carotenoids increased in all participants, various aspects of visual function only improved in Michael Mosley following testing in labs at City. Colour sensitivity, ability to see fine spatial detail in low contrast and many aspects of low light level vision improved significantly in the presenter after supplementation. Vision in the smoothie-ingesting volunteers appeared unaffected despite their increased carotenoid levels.
Why positive results were only observed in one participant is an open question. Certainly there were many differences in his treatment compared to that of the other volunteers that might contribute to the conflicting findings. Various aspects of Michael Mosley’s vision were measured at City, University of London using the Advanced Vision and Optometric Tests (AVOT) developed to reveal small changes in visual performance. The smoothie-drinking volunteers were assessed using another battery of examinations in Waterford, Ireland.
Perhaps the tests done in London were simply more sensitive and able to reveal subtle differences in visual function than the Irish ones? There may well be other explanations too. Michael Mosley took supplements in pill form rather than as a drink. But above all, he may have been starting from a different physiological baseline compared to the other participants. His vision was normal before supplementation started, but not outstanding. It is conceivable that supplements were effective for Michael Mosley for some unknown physiological reason, but that they would have little effect on the visual function of people with better vision.
Certainly, the results are intriguing and it is encouraging to find even one positive result. But it is far too early to say that taking supplements would improve visual function generally. Furthermore, it must not be forgotten that taking carotenoid supplements has dangers too. Smokers and heavy drinkers, for example, are more likely to get certain cancers if they take such supplements.
What is clear is that a large, well-funded, controlled trial is required before any firm conclusions can be reached and it is far too soon to recommend everyone to take a magic pill to improve their vision.
At the meeting other fundamental aspects of human macular pigment were also discussed by Professor John Mellerio in the afternoon’s first lecture. Two presentations followed by Dr Tony Robson (with Jack Moreland), from Moorfields Eye Hospital and the UCL Institute of Ophthalmology, and Dr Irene Ctori, a lecturer in the Division of Optometry and Visual Sciences at City, which examined aspects the distribution of macular pigment within the retina. Both revealed a variety of different densities and spatial distribution profile which, perhaps surprisingly, did not change with age and were influenced by ethnicity.
A talk by Dr Mike Powner, a researcher at City in the Division of Optometry and Visual Sciences at City, also explained the chemistry behind macular pigment and its involvement in the disease Macular telangiectasia (Mac Tel). While Dr Marisa Rodriguez-Carmona, also from the Division of Optometry and Visual Sciences, summarised earlier research at City, University of London on the effects of carotenoid supplementation on the eye.