27.01.2012

Is vitamin D the key to healthy eyesight?

Is vitamin D the key to healthy eyesight?

By Adrian Galbreth

Almost every month, a new so-called superfood comes along that experts claim can prolong people's lives or help to cure ailments, but now it seems there is strong evidence that one particular nutrient can have significant benefits for vision.

According to a team of researchers funded by the Biotechnology and Biological Sciences Research Council (BBSRC) vitamin D reduced the effects of ageing in mouse eyes and improved the vision of older mice significantly.

The specialists hope that this might mean that vitamin D supplements could provide a "simple and effective" way to combat age-related eye diseases in people, including macular degeneration (AMD), which is the single biggest cause of blindness in the developed world.

The study, which was carried out by a team from the Institute of Ophthalmology at University College London and published in the journal Neurobiology of Ageing, was led by Professor Glen Jeffery.

He explained that at the back of the eyes of mammals, like mice and humans, is a layer of tissue that we know as the retina, which detects light as it comes into the eyes and then send messages to the brain, allowing us to see.

As it is a demanding job, and the retina requires proportionally more energy than any other tissue in the body, it needs a good supply of blood, but ageing produces debris and subsequent progressive inflammation.

This results in the decline of up to 30 per cent of the numbers of light receptive cells in the eye by the time people hit 70 and can lead to poorer vision.

However, in the new study, Professor Jeffery noted that when old mice were given vitamin D for just six weeks, inflammation was reduced, the debris was partially removed, and their vision was improved.

Two major changes were observed taking place in the eyes of the mice that he believes accounted for this improvement, with the first being the number of potentially damaging cells, called macrophages, being reduced considerably in the eyes of the mice given vitamin D.

Macrophages are an important component of immune systems which work to fight off infections, but by combating threats to the aged body they can sometimes bring about damage and inflammation.

Giving mice vitamin D not only led to reduced numbers of macrophages in the eye, but also triggered the remaining macrophages to change to a different configuration and, rather than damaging the eye, the researchers think that in their new configuration macrophages actively worked to reduce inflammation and clear up debris.

Secondly, the experts noticed a reduction in deposits of a toxic molecule called amyloid beta in the eyes, which accumulates with age.

Inflammation and the accumulation of amyloid beta are known to contribute to an increased risk of age-related macular degeneration (AMD), and so researchers think that, based on their findings in mice, giving vitamin D supplements to people who are at risk of AMD might be a simple way of helping to prevent the disease.

Professor Jeffery explained: "People might have heard of amyloid beta as being linked to Alzheimer's disease and new evidence suggests that vitamin D could have a role in reducing its build up in the brain. So, when we saw this effect in the eyes as well, we immediately wondered where else these deposits might be being reduced."

He added that finding that amyloid deposits were reduced in the blood vessels of mice that had been given vitamin D suggests that the supplement could not only be useful in helping to prevent a range of age-related eye problems, but a range of health issues, including heart disease.

The experts now need to run full clinical trials in humans before they can confirm that older people should start taking vitamin D supplements, but noted that there is now growing evidence that many people in the developed world are deficient in vitamin D and this could be having significant health implications.

by Emily Tait


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