Anthocyanin can enhance the eye’s function of “Dark Adaptation” which is defined that the eye gradually adapts from bright sunlight to complete darkness. Generally, when we move from very bright to very dark places suddenly, we cannot see our surroundings well. The reason the eye cannot adapt to the darkness promptly is because the pupil is not fully widened yet. The less the level of light, the wider becomes the pupil to gather light. It takes approximately 20 – 30 minutes for the eye to adapt to the darkness since the light does not reach visual cells of retina. However, if we take Anthocyanin, “Dark Adaptation” is improved to some extent because visual cells react the faint light sensitively by the effect of Anthocyanin. In addition, we can see better than other people once the eye is adapted to the darkness. Thus, if we take regularly such foods as black soybean and blueberry that contain plenty of Anthocyanin, we can see well even in the darkness.
Anthocyanin has an effect to activate the re-synthesis of a pigment on the retina called Rhodopsin which is a visual material distributed widely on the retina except a macular region. The retina has two kinds of visual cell. One is a pyramidal cell that senses the color in the light, and the other is a rod that senses brightness in the dark. Rhodopsin is contained in the rod and more than 100 millions of its molecules exist in an eye. When the light reach the retina in the dark, the signal generated by decomposition of Rhodopsin will be transmitted to the brain.
Re-synthesis of Rhodopsin
The intake of Anthocyanin activates re-synthesis of Rhodopsin, and improves eyesight in the dark. Once Rhodopsin decomposes, it will have to be re-synthesized. If Rhodopsin is not re-synthesized, it will be depleted and we will not be able to sense the light in the dark. Therefore, Rhodopsin is to be automatically re-synthesized and the rate of this re-synthesis will affect “Dark Adaptation”.
It is found that C3G, one of Anthocyanin has a strong effect to activate re-synthesis of Rhodopsin.
Vitamin A is also involved in this re-synthesis since Retinal which is one of compositions of Rhodopsin is composed through Vitamin A. The lack of Vitamin A causes “night blindness” owing to stop of Rhodopsin synthesis.
Thus, the activation of Rhodopsin re-synthesis and enhancement of “Dark Adjustment” can be expected by taking Vitamin A as well as Anthocyanin.