Since I love my science and research, I took it upon myself to spend my spare time reading every published article on SD and vitamin A to find out more about the mechanisms at play in the eye causing problems and what evidence exists to support these theories. The earliest article I found was published in 2008 and all used mouse models for investigations.
A paper published in Cell Death and Disease this year gives a good overview of the mechanism leading to vision loss and how Vitamin A is implicated. Essentially, SD is caused by an accumulation in the RPE of Vitamin A dimers (dimers are two molecules joined chemically), which are known as A2E (shortened version of the chemical name). Using an in vivo model, they found that increased A2E led to greater cell death. A word that always comes up when talking about SD is lipofuscin which is the yellow-brownish pigment deposits seen on a retinal scan used to diagnose the condition. Tying it all together, A2E derived from vitamin A is a retinal lipofuscin which is causing the damage and subsequent vision loss. These findings support earlier studies in mice such as articles n the Journal of Biological Chemistry and Investigative Ophthalmology and Visual Science which both looked at the effects of vitamin A, SD and mice demonstrating that higher doses of vitamin A led to increased lipofuscin development.
Another paper in the Journal of Biological Chemistry also used a mouse model to investigate the effects of A2E and also oxidative stress. It was found that A2E increased inflammation in the RPE, which is an important finding for prospective treatment solutions.
There are no studies performed in humans on the effects of vitamin A probably because it is not exactly ethical to get a group of SD patients and give them high doses of vitamin A and see whether they deteriorate! Despite this, the research is available to support that vitamin A is indeed causing damage in the eye and leading to vision loss. The continuing research has led to greater understanding on the different components at play and, no doubt, will help in the future to develop therapies.
So now we know vitamin A is not our best friend, where do we go from here? Part 2 will discuss diet and vitamin A and how we can ensure not to overload vitamin A and contribute to the SD process.
