Ascorbic acid

Studies in people

• Concern

  Kidney stone risk³

  Eating ascorbic acid may raise oxalate in urine, which is linked to kidney stones in some people.

• Benefit

  Immune system support⁴

  Vitamin C helps immune cells work and may help prevent and treat chest and other infections.

• Open question

  Long-term disease prevention⁶

  Vitamin C may help prevent chronic diseases, but studies disagree and scientists do not yet know for sure.

• Benefit

  Common cold symptoms⁷

  Vitamin C taken regularly may shorten how long a cold lasts and how bad it feels.

• Open question

  Heart and cancer risk⁸

  Whether vitamin C in fruits and vegetables protects against heart disease and cancer is not yet known.

• No harm found

  Colds and infections⁹

  Vitamin C supplements don't seem to prevent colds or chest infections in most well-fed people.

• Benefit

  Immune health and colds¹⁰

  Some vitamin C forms, like Calcium ascorbate EC, may raise vitamin C in immune cells and shorten severe cold symptoms.

• Benefit

  Iron absorption from food¹¹

  Ascorbic acid helps the body absorb nonheme iron from vegetable meals, and this rises with the amount present.

• Open question

  Fertility treatment success¹²

  In women having fertility treatment, ascorbic acid supplements raised follicle levels, but the higher pregnancy number was not statistically significant.

• Benefit

  Gout risk¹³

  People who ate more vitamin C in food were less likely to have gout, though vitamin C pills showed no link.

• Benefit

  Heart and blood vessels¹⁵

  In older people, eating more ascorbic acid was linked to better cholesterol and blood fat levels.

• Benefit

  Mouth cancer risk¹⁶

  In adults in Southern China, eating more vitamin C was linked to fewer new cases of oral cancer.

• Benefit

  Vitamin deficiency on restricted diet¹⁷

  People with hereditary fructose intolerance on a lifelong restricted diet often had low vitamin C, and ascorbic acid supplements raised their levels.

• Benefit

  Frailty risk in women¹⁸

  In Korean women, more fruits, vegetables and dietary ascorbic acid was linked to lower frailty risk, but ascorbic acid pills were not.

Study type not stated

• Benefit

  Bone strength and sleep²⁰

  Ascorbic acid may help bone density and sleep, but scientists do not yet know if it prevents osteoporosis.

How it’s made and used

• Diet and disease prevention⁵

  People cannot make ascorbic acid, so it must come from food; too little causes scurvy.

• Falling nutrient intake¹⁴

  Vitamin C intake from food and drinks fell 23% over 20 years, with more people now falling short.

• Daily nutrient requirements¹⁹

  New guidance sets how much ascorbic acid men, women, smokers and children should get daily.

The signal at the top counts the findings in people and in animal and lab studies. A concern in studies of people outranks animal and lab studies, and “No concerns” needs at least one finding in people. When most findings in people point one way, the page leans that way (“Mostly”), and every finding is still shown. Findings whose study type is not stated are shown but not counted. This page is a reference, not medical advice. It describes what regulators and published research say. Talk to a doctor or dietitian about your own diet.

Expert panels that weigh all the research. Shown for context: the signal at the top does not count them.

• UN and WHO food additive experts (JECFA), 1981

  No daily limit needed (“ADI not specified”, JECFA’s term for very low toxicity).