How are temporary blindness, white spots, vitamin A, and beta-carotene related?
Vitamin A and Vision
The retina of the eye contains about 6 to 7 million cone cells and 100 million rod cells, and each contains about 30 million molecules of retinal-containing visual pigments. Retinal is the active form of vitamin A. Visual activity leads to repeated small losses of retinal and requires its constant replenishment from retinol in the blood, which brings a new supply from body stores. This is where nutrition plays a role—ultimately, vitamin A and beta-carotene are the source of all the retinal in the pigments of the eye.
Seeing a sudden bright light when the eyes are accustomed to dark destroys much more retinal than seeing light by day, and if the body’s vitamin A stores are marginal, this can lead to the early vitamin A-deficiency symptoms of night blindness.
The eye is especially vulnerable to retinal destruction at night for three reasons.
First, the pupil opens wide at night to allow as much light as possible to enter the eye.
Second, a shadowing pigment that protects the rods by day withdraws at night, leaving them exposed.
Third, there are many more rods than cones. Hence, if a bright light suddenly shines at night through the wide-open pupil onto the unprotected rods, much of the pigment in them is bleached and momentarily inactivated. More retinal than usual is freed, and more is lost. A moment passes before the pigments regenerate and sight returns.
As I mentioned earlier, if the vision doesn’t return immediately, and you see spots, you need more vitamin A or beta-carotene.
Conversion of Beta-carotene to Vitamin A
Beta-carotene is a type of carotenoid, which is a potent antioxidant. Carotenoids are red, orange, green, or yellow compounds naturally present primarily in many types of fruits and vegetables. Carotenoids are considered provitamins because they can be converted to active vitamin A.
Best Foods Sources of Beta-carotene (and therefore Vitamin A activity)
Deep Green: Spinach, kale, collard greens, Swiss chard, Chinese cabbage, turnip greens, broccoli, butterhead lettuce, romaine lettuce, red leaf lettuce, basil, coriander, seaweed
Bright Orange: apricots, cantaloupe, carrots, squash, sweet potatoes, pumpkin, paprika
Bright Red: Hot red chili peppers, red bell peppers
Bright Yellow: butternut squash
This is just another example of how important fruits and vegetables are. I consider my vision one of the most important functions of my body. All it takes is a well-balanced diet including two to three servings of a foods containing beta-carotene to help keep those eyes healthy.
In Health and Happiness,
Kelly Harrington, MS, RDN
Registered Dietitian Nutritionist for Healthy Goods