The “surprising discovery” by researchers Oregon Health & Science University indicates that vitamin C may be needed for correct functioning of retinal cells, which in turn may have implications for the central nervous system.
In order for retinal cells to function properly, “we found that cells need to be 'bathed' in relatively high doses of vitamin C, inside and out,” explained Henrique von Gersdorff, PhD, a senior scientist at OHSU's Vollum Institute and a co-author of the study.
“Because the retina is part of the central nervous system, this suggests there's likely an important role for vitamin C throughout our brains, to a degree we had not realized before.”
According to findings published in the Journal of Neuroscience, this new research used goldfish retinas, which the researchers claim have the same overall biological structure as human retinas.
The dietary supplement and functional food market for eye health is being driven by several major forces: An aging population, unhealthy diets, an increased demand for natural ingredients and rising healthcare costs.
Most of the science in this area has focused on the macula – a yellow spot of about five millimeters diameter on the retina – and a corresponding condition called age-related macular degeneration (AMD).
The yellow color is due to the content of the carotenoids lutein and zeaxanthin, which we derive from the diet, and these two nutrients dominate the $138m US eye health ingredients market, according to Frost & Sullivan (2008 data).
In addition to lutein and zeaxanthin, ingredients such as astaxanthin, beta-carotene, and bilberry extracts, as well as the vitamins A, C and E, are also included in eye health formulations.
Putting the C in CNS
The new research indicates that vitamin C may not only benefit the eye, but have wider implications for the functioning of the central nervous system (CNS).
According to the OHSU scientists, the benefits revolve around special receptors in the retina and brain called GABA-type receptors, which reportedly modulate the rapid communication between brain cells by acting as an inhibitory ‘brake’ on excitatory neurons in the brain.
When vitamin C is no longer present, the OHSU researchers report that these receptors stopped functioning properly.
Vitamin C reservoir
Dr von Gersdorff and his co-workers note that the function of vitamin C in the brain is not well understood. However, vitamin C stores in the brain are known to be the last to be depleted in times of vitamin C deprivation, they added.
“Perhaps the brain is the last place you want to lose vitamin C,” he said.
Vitamin C deficiency results in the condition called scurvy, and one of the common symptoms of which is depression. The researchers postulated that their new findings may help explain this observation.
The findings may also have implications for other diseases that are caused by malfunctioning nerve cells in the retina and brain, like glaucoma and epilepsy, said the researchers
“Maybe a vitamin C-rich diet could be neuroprotective for the retina – for people who are especially prone to glaucoma,” von Gersdorff said. “This is speculative and there is much to learn. But this research provides some important insights and will lead to the generation of new hypotheses and potential treatment strategies.”
Source: The Journal of Neuroscience
Volume 31, Issue 26, Pages 9672-9682, doi:10.1523/JNEUROSCI.5157-10.2011
“Allosteric Modulation of Retinal GABA Receptors by Ascorbic Acid”
Authors: C.I. Calero, E. Vickers, G. Moraga Cid, L.G. Aguayo, H. von Gersdorff, D.J. Calvo