Vitamin C is a nutrient from fruit and vegetables. In trials, daily doses made colds a little shorter and lowered blood pressure a little.
Ask a doctor or pharmacist before you take vitamin C supplements if one of these applies to you:
Vitamin C (ascorbic acid) is a vitamin that dissolves in water. People must get it from food, because the human body cannot make it.[1] Fruits and vegetables are the best sources: half a cup of raw red pepper has 95 mg, a medium orange 70 mg and a kiwifruit 64 mg.[1] Most supplements contain ascorbic acid; other forms are sodium ascorbate, calcium ascorbate and Ester-C.[1]
Its clearest use is to prevent and treat scurvy, the disease of vitamin C deficiency.[1] For immune support, taking at least 200 mg every day made colds 8% shorter in adults and 14% shorter in children.[3] For heart and circulation, short trials found that it lowered systolic blood pressure by about 4 mmHg and improved the function of blood vessels.[4][5] It also helps the gut absorb iron from plant foods.[1] Large trials of 500 mg a day for 8 and 9.4 years found no fewer heart attacks or strokes.[6][7]
Vitamin C has low toxicity at usual doses.[1] High doses can cause diarrhea, nausea and stomach cramps, and the US upper limit for adults is 2,000 mg a day.[1] In men, supplements of 1,000 mg a day or more went with more kidney stones.[2] People with hemochromatosis, kidney stones or cancer treatment should ask a doctor first.[1]
The human body cannot make vitamin C, so it must come from food or supplements.[1] The gut and the kidneys keep the level in the blood within a narrow range.[1][8]
A transporter in the intestine takes up vitamin C. The gut absorbs 70% to 90% of 30 to 180 mg a day, but less than 50% of doses above 1 g a day.[1]
Cells take vitamin C from the blood with a second transporter. Levels are highest in white blood cells, the eyes, the adrenal glands, the pituitary gland and the brain.[1]
Vitamin C is needed to make collagen, an essential part of connective tissue, and also L-carnitine and some neurotransmitters, the messengers of nerve cells. It helps the gut absorb iron from plant foods.[1]
Neutrophils, white blood cells that kill germs, collect vitamin C. A 2017 review says that it can help them move toward germs, take them in and kill them.[9]
The kidneys pass the extra into urine. In a study of 7 volunteers, single doses of 500 mg or more were absorbed less, and the absorbed extra left in urine.[8]
Each row is one benefit. The square shows the grade and the number of studies. Open a row to see the most trusted studies.
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The cold trials in a Cochrane review gave at least 200 mg a day, and the 29 blood pressure trials in a 2012 review a median of 500 mg a day.[3][4] The US daily allowance for adults is 90 mg for men and 75 mg for women.[1]
Most supplements contain ascorbic acid. The body absorbs it as well as the vitamin C in orange juice or broccoli. Sodium ascorbate, calcium ascorbate and Ester-C are other forms.[1]
In the trials that found shorter colds, people took vitamin C every day, before any cold began. Taken only after symptoms started, it had no consistent effect.[3]
Most studies gave 250 to 500 mg a day, for 1 to 3 months.
The counts are study groups. A study group is one set of people in a study who took the same dose. One study can have several groups. These are amounts from studies, not advice for you.
409 of 688 study groups took vitamin C with something else. This shows what studies gave together, not what works together.
What studies used when they gave vitamin C for one goal, or to a group of people.
Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.
12 questions in 4 groups. Open one for the short answer; each has its own page with the full answer and sources.
In the US, adult men need 90 mg a day and women 75 mg, 85 mg in pregnancy and 120 mg while breastfeeding.[1] People who smoke need 35 mg more.[1] In the EU, EFSA set 110 mg for men and 95 mg for women.[11] Five servings of fruit and vegetables a day can give more than 200 mg.[1]
Severe deficiency causes scurvy. Its signs can appear within 1 month on less than about 10 mg a day.[1] First come tiredness and inflamed gums; later come small bleeds under the skin, bruises, joint pain, slow wound healing, bleeding gums and loose teeth.[1] Scurvy is rare in developed countries. People who smoke, eat few kinds of food or absorb nutrients poorly are more likely to get too little vitamin C.[1]
In most people, taking vitamin C every day does not prevent colds, but it makes them a little shorter: by 8% in adults and 14% in children.[3] In marathon runners, skiers and soldiers on exercises in the subarctic, it halved the risk of a cold.[3] Started only after a cold began, it had no consistent effect.[3]
Short trials found a small fall. A 2012 review of 29 trials found that systolic pressure fell by 3.84 mmHg, with a median of 500 mg a day for 8 weeks.[4] A 2023 review of 20 trials found a fall of 3.0 mmHg, larger in people with high blood pressure or diabetes.[10] Two large trials of 500 mg a day for 8 and 9.4 years found no fewer heart attacks or strokes.[6][7]
Yes, from a meal: vitamin C helps the gut absorb nonheme iron, the iron in plant foods.[1] In a test meal, 31 mg of vitamin C raised iron absorption by 56% in women of normal weight, but by only 28% in women with overweight or obesity.[13] A trial gave 440 adults with iron deficiency anemia a 100 mg iron tablet every 8 hours for 3 months, with or without 200 mg of vitamin C.[14] The vitamin C did not raise hemoglobin or ferritin more than iron alone.[14]
Large trials found that it does not. In 14,641 male doctors, 500 mg a day for 8 years did not lower heart attacks, strokes or heart deaths.[6] In 8,171 women at high risk, 500 mg a day for 9.4 years did not change heart events, cancer or cancer deaths.[7][1] A 2022 review for the US Preventive Services Task Force found little or no benefit of vitamin and mineral supplements against heart disease and cancer in healthy adults.[15] For vitamin C, the evidence of benefit was unclear, small or absent.[15]
Skin holds a lot of vitamin C, which helps make collagen and helps protect skin from damage by UV light.[16] It is not well known whether creams and serums do more than enough vitamin C from food.[16] In one trial, 30 people used a serum with 10% vitamin C and phytic acid twice a day for 3 months.[17] It faded sun spots more than the same serum without the active parts.[17]
Age-related macular degeneration (AMD) is one of the leading causes of vision loss in older people.[1] The AREDS trial followed 3,640 people aged 55 to 80 with signs of AMD for a mean of 6.3 years.[18] In those who took 500 mg of vitamin C with vitamin E, beta carotene and zinc, the odds of advanced AMD were 28% lower than with placebo.[18] The antioxidants without zinc did not lower the odds significantly.[18] The evidence does not show that vitamin C, alone or with other antioxidants, changes the risk of getting AMD.[1]
The most common effects of high doses are diarrhea, nausea and stomach cramps.[1] The US upper limit for adults is 2,000 mg a day.[1] EFSA set no limit, but it considered that 1,000 mg a day on top of the usual diet is not linked to gut side effects.[12] In men, supplements of 1,000 mg a day or more went with more kidney stones.[2] In people with hemochromatosis, long use of high doses may add to the iron in the body.[1]
In men it may. In 40,536 US men followed for about 11 years, supplements of 1,000 mg a day or more went with a 19% higher risk; in 156,735 women there was no link.[2] A 2019 review of 4 studies found the same pattern.[19] The clearest risk is in people who already have high oxalate in their urine.[1]
Pregnant women need 85 mg a day (80 mg at 14 to 18 years), and the US upper limit in pregnancy is 2,000 mg a day (1,800 mg at 14 to 18 years).[1] A 2015 Cochrane review pooled 29 trials of vitamin C, alone or with other supplements, in 24,300 women.[20] It found no clear effect on stillbirth, preterm birth, the growth of the baby or pre-eclampsia.[20] It found no convincing evidence of other important benefits or harms; in one trial, women on vitamin C reported more abdominal pain.[20]
Plain ascorbic acid is absorbed as well as the vitamin C in fruit and vegetables, and it costs less than other forms.[1] Calcium ascorbate, Ester-C and liposomal vitamin C gave higher levels in some blood measures.[21][22] The 2025 review of these forms said more research is needed to show effects on immune health.[21]
