What is vitamin C?

In one line

Vitamin C is a water-soluble vitamin that the human body cannot make, so it must come from food.

What is vitamin C?
The vitamin most seen on fruit and supplement tubs
Vitamin C is the name you see most often in orange juice ads and on supplement tubs. This post explains what vitamin C is, what it does in the body, where it is found, how much is needed a day, and what happens when people take a lot.
In one line
A water-soluble vitamin you must eat
Nutrients the body needs in small amounts to grow and work properly are called 'vitamins'. Vitamin C is one that dissolves in water. Humans cannot make it, so it must come from food. Its chemical name is 'ascorbic acid'.
Why can't humans make it?
We lost the enzyme that makes it
A protein that helps chemical reactions in the body is called an 'enzyme'. Most animals have an enzyme that makes vitamin C, so they make their own. Humans and other primates, guinea pigs, bats and some others lost this enzyme and rely on food.
Job one: collagen
The protein that builds skin, tendons and blood vessels
The tough protein that makes up skin, tendons and blood vessels is called 'collagen'. Vitamin C is essential for the body to make collagen. That is why it is also used in healing wounds and keeping bones, cartilage and teeth in good shape.
Job two: antioxidant
It blocks substances that damage cells
When the body uses food or breathes in tobacco smoke, unstable oxygen substances that damage cells are made. A substance that stops them from damaging cells is called an 'antioxidant'. Vitamin C is a leading antioxidant.
Job three: iron absorption
It helps iron from food get in
When nutrients pass from the gut into the blood, it is called 'absorption'. In the gut, vitamin C changes iron from food into a form that is easier to absorb, helping iron get in. It does this even at the small amounts found in normal food.
Too little causes scurvy
Bleeding gums and slow-healing wounds
A very severe lack of vitamin C is called 'scurvy'. Because collagen is not made properly, the gums bleed, bruises form easily, and wounds heal slowly. The body cannot store vitamin C for long, so scurvy appears when it is not eaten regularly.
Where is it found?
About 70 mg in one orange
Vitamin C is in fruits and vegetables. Citrus fruits such as oranges and grapefruit, kiwi, strawberries, broccoli and peppers are rich in it. One medium orange has about 70 mg. Cooking or long storage lowers the amount.
How much a day?
The adult recommendation is 75 to 90 mg
The US recommended amount for adults is 90 mg a day for men and 75 mg for women. Smoking or breathing secondhand smoke adds 35 mg a day. The daily value on US food labels is also 90 mg.
When people take too much
Over 2,000 mg a day is not recommended
When more than 500 mg is taken at once, the share absorbed drops, and the extra that is absorbed leaves in the urine. US guidance does not recommend more than 2,000 mg a day. Stomach upset and diarrhea are the listed problems at amounts this large.
Common misconception
The extra leaves in urine, so taking a lot is fine?
No. Taking a lot of vitamin C raises 'oxalate' in urine, a building block of kidney stones. Men who took 1,000 mg or more of vitamin C supplements a day had about 1.2 times the risk of kidney stones of men who took none. This link was not seen in women.
Summary
Water-soluble, and humans can't make it
Vitamin C is a water-soluble vitamin that the human body cannot make, so it must come from food. It helps make collagen, works as an antioxidant, and helps absorb iron. The fact that extra leaves in urine does not mean taking a lot is harmless. Related terms: collagen, scurvy, antioxidant.