Vitamin A and Night Blindness
The orange and yellow colors of carrots and other brightly colored fruits and vegetables are due to betacarotene and several other related chemicals called carotenoids.
Your body can convert some of these carotenoids to retinol, which is the form of vitamin A that your body uses.
Human beings can easily get all the vitamin A they need by eating dark green and deep yellow or orange fruits and vegetables.
Cats, on the other hand, need to get their vitamin A in the form of retinol, which comes only from an animal source.
If you wanted to develop a plant-based diet for a cat, you would have to supplement it with some synthetic retinol (among other things).
One of the symptoms of mild vitamin A deficiency is night blindness, or the inability to see in low light conditions. Severe vitamin A deficiency causes permanent blindness and problems with the immune system.
The safest way to meet your need for vitamin A is to eat dark green or deep yellow or orange vegetables and fruits. Your body converts the carotenoids from those foods to vitamin A only on an as-needed basis.
Even if you overdose on carrot juice, the worst that’s likely to happen is that your skin will turn yellow.
On the other hand, an overdose of retinol can cause severe side effects, such as permanent blindness or even death.
Many Americans aren’t getting the recommended amount of vitamin A, but that’s mainly because most of us need to eat more fruits and vegetables.
Unfortunately, our agricultural subsidies are being spent on corn and soybeans instead of on fruits and vegetables. These subsidies are promoting the production and consumption of animal-based foods and processed foods.
So our tax dollars are being used to make dangerous food cheap, instead of making healthy food affordable.
Although most Americans would benefit from eating more fruits and vegetables, a severe vitamin A deficiency is actually rare in the United States.
Most cases occur in people who do not or cannot eat properly (such as alcoholics) and in people with digestive diseases (such as cystic fibrosis) that prevent them from absorbing vitamins from their food. In contrast, vitamin A deficiency is a major cause of blindness and death among children in poor countries.
Today, children in poor countries may receive a periodic high-dose vitamin A supplement, often in coordination with vaccination programs.
When people get a lot of beta-carotene from their diet, it is because they’re eating a lot of fruits and vegetables. This tends to make them healthier than the people who are eating the standard American diet.
Some people hoped that they could get the same benefits by adding beta-carotene in pill form to the standard American diet, instead of switching to a healthy diet.
However, the beta-carotene supplement seems to do more harm than good.
One large clinical trial (the CARET study) involving people at high risk for lung cancer showed more lung tumors, more heart attacks, and more deaths among the subjects who received pills containing beta-carotene and retinyl palmitate (another form of vitamin A) than in patients who received placebo pills.
Why did the beta-carotene supplement do more harm than good?
In nature, there’s no such thing as a concentrated dose of pure beta-carotene.
Fruits and vegetables provide beta-carotene in combination with other carotenoids. Your body probably needs a balanced mixture of several carotenoids, not a concentrated dose of only one of them.
The results of the CARET study reinforce a message that I have seen in every nutrition textbook I have ever read. You should get your vitamins from foods, not from pills.