Vitamin C (as calcium ascorbate)

What is vitamin C?

Vitamin C, or ascorbic acid, is a water-soluble vitamin that people must get from food because the body cannot make or store much of it. It is needed to make collagen, the protein that gives structure to skin, blood vessels, cartilage and parts of the eye, and it works as an antioxidant that helps protect cells from damage by free radicals. It also helps the body absorb iron from plant foods. Citrus fruits, kiwi, strawberries, peppers, broccoli and tomatoes are rich sources. Supplements use ascorbic acid or buffered mineral salts such as calcium ascorbate, which some people find gentler on the stomach.

What the research says

Vitamin C deficiency causes scurvy, with bleeding gums, easy bruising, poor wound healing and joint pain. In eye health research, vitamin C is best known as one of the antioxidants in the AREDS and AREDS 2 formulas. The National Eye Institute’s AREDS 2 recommendation includes 500 mg of vitamin C, along with vitamin E, zinc, copper, lutein and zeaxanthin, for people who have intermediate age-related macular degeneration or late AMD in one eye. In those groups, the combination lowered the chance of losing central vision. The trials tested the whole formula, so they do not show what vitamin C does alone, and the NEI says the supplements are not intended for people without AMD.

Outside of AMD, there is little evidence that extra vitamin C improves eyesight, relieves tired eyes or prevents eye disease in people who already eat enough fruits and vegetables. Most US adults reach the RDA through diet.

How it’s used in supplements

Vitamin C is one of the most common supplement ingredients, used in multivitamins, immune formulas and eye formulas. Doses range from about 60 mg to 1,000 mg or more. MedlinePlus notes that serious side effects from too much vitamin C are rare because the body excretes the excess, but amounts above 2,000 mg a day are not recommended, as they can cause stomach upset and diarrhea and, rarely, kidney stones. Large doses are also not recommended during pregnancy. People with a history of kidney stones or iron overload conditions should ask a doctor before taking high-dose vitamin C. Vitamin C can also interfere with some lab tests, including certain blood sugar readings, so tell your healthcare team if you take it.

For eye health specifically, the most useful takeaway is that vitamin C works as part of a team. If an eye doctor has recommended an AREDS 2 supplement, the 500 mg of vitamin C in it is intended to be taken with the other nutrients at their tested doses. For everyone else, a diet with plenty of colorful fruits and vegetables usually provides enough vitamin C, along with fiber and other protective plant compounds that a capsule does not.