Quick answer

Vitamin C is a vitamin your body cannot make. It is needed for collagen in skin, gums and blood vessels, works as an antioxidant, helps you absorb iron from plant foods and has a role in normal immune function. Adults need 75 to 90 mg a day, which most people get from fruit and vegetables.^1,2,3

Key facts

Adult men need 90 mg of vitamin C a day and women 75 mg, and people who smoke need 35 mg more.²
Half a cup of raw red pepper has 95 mg, more than a medium orange at 70 mg.¹
The adult upper limit is 2,000 mg a day from food and supplements combined.²
Research has not shown any form of vitamin C to be better than the others, and plain ascorbic acid is the most common.^1,2

What vitamin C is and what it does

Humans, unlike most animals, cannot make vitamin C, so it must come from the diet.¹

Inside the body, vitamin C has several jobs at once. The enzymes that build collagen need it, and so do the ones that make L-carnitine and some chemical messengers in the brain. It works as an antioxidant, mopping up free radicals and helping to recycle vitamin E, and it raises the amount of iron you take up from plant foods.¹

The body holds about 300 mg to 2 g of vitamin C. White blood cells, the eyes, the adrenal and pituitary glands and the brain hold the highest concentrations.¹

The body keeps a tight grip on its vitamin C. Moderate amounts are absorbed well and large ones less so, and whatever is not needed leaves in urine. That is why blood levels flatten out once intake passes about 200 mg a day.¹

What the evidence shows

Each claim below carries a grade and the amount behind it. Four describe well-established jobs of the vitamin, which depend on getting enough rather than on taking extra. The skin measurement result is early: it comes from one small trial.

Contributes to the normal function of the immune system*^1,3,4,5

Moderate evidence

A well-established nutrient function. NIH describes roles for vitamin C in both the first-line and the learned parts of the immune system: it helps keep barrier tissues intact and helps white blood cells multiply and do their work, and these cells hold far more vitamin C than blood does. EU regulators permit this wording for foods that are at least a source of vitamin C. It is about getting enough. NIH notes that when people are not short of a nutrient, routine supplements probably add little, and most people in the United States get enough vitamin C from food.

Amount studied: Recommended intake: 75 mg a day for women and 90 mg for men, from food and supplements

Contributes to normal collagen formation for the normal function of skin, gums, teeth, bones, cartilage and blood vessels*^1,3,6

Moderate evidence

A well-established nutrient function. NIH states that vitamin C is required to make collagen, an essential part of connective tissue, and EU regulators permit this wording, as six separate statements, for foods that are at least a source of vitamin C. Normal skin holds high levels of vitamin C. The claim describes what the body needs vitamin C for. It does not show that extra vitamin C changes how skin looks in someone who already gets enough, and how creams and serums compare with getting enough in the diet is poorly understood.

Amount studied: Recommended intake: 75 mg a day for women and 90 mg for men, from food and supplements

Contributes to the protection of cells from oxidative stress*^1,2,3,7

Moderate evidence

A well-established nutrient function. NIH describes vitamin C as an antioxidant that limits damage from free radicals and helps regenerate vitamin E, and EU regulators permit this wording for foods that are at least a source of vitamin C. It describes a normal function, not a measured health outcome: in healthy young women given 30 to 2,500 mg a day, blood and urine markers of the body's own oxidative damage did not change at any dose.

Amount studied: Recommended intake: 75 mg a day for women and 90 mg for men, from food and supplements

Increases iron absorption*^1,3,8,9

Moderate evidence

A well-established nutrient function, permitted in this wording by EU regulators for foods that are at least a source of vitamin C. NIH says vitamin C raises absorption of nonheme iron, the form in plant foods and fortified foods, and that mixed diets with meat, seafood and vitamin C let the body absorb about 14% to 18% of their iron, against 5% to 12% for vegetarian diets. In a typical Western diet these effects make little difference to most people's iron status.

Amount studied: Vitamin C eaten in the same meal as plant sources of iron

May raise the antioxidant activity measured in skin*¹⁰

Early evidence

One small placebo-controlled trial. Thirty-three volunteers took vitamin C or a placebo for four weeks, and the skin's ability to neutralize free radicals was measured with a magnetic resonance method. It rose 22% with 100 mg a day and 37% with 180 mg a day, and did not change with placebo. In the people also measured at two weeks, the rise had already reached its peak. It is one study of a laboratory measure, not of how skin looks or ages.

Amount studied: 100 or 180 mg a day for four weeks

All of this is about vitamin C you eat or swallow. Serums and creams are a different product, and a 2017 review found their value, compared with simply getting enough in the diet, poorly understood.⁶

How much you need

Adult men need 90 mg of vitamin C a day and adult women 75 mg, from food and supplements combined.^1,2

People who smoke need 35 mg more vitamin C a day than people who do not, in part because smoke raises the amount the body uses.^1,2

Vitamin C for adults, per day¹
Who	Recommended	Upper limit, all sources
Men	90 mg	2,000 mg
Women	75 mg	2,000 mg
Pregnancy	85 mg	2,000 mg
Breastfeeding	120 mg	2,000 mg

The gap between need and limit is wide. The dosage guide sets out the amounts for every age, how much of each dose is absorbed, and where white blood cells fill up.

Food comes first

Fruits and vegetables are the best sources, especially citrus fruits, red and green peppers, kiwifruit, broccoli, strawberries, Brussels sprouts and cantaloupe. Some breakfast cereals have vitamin C added.¹

Five varied servings of fruits and vegetables a day can provide more than 200 mg of vitamin C.¹

Most people in the United States get enough vitamin C from food and drink. People who smoke or breathe secondhand smoke, and people who eat a narrow range of foods, are more likely to fall short.²

Which form

Most supplements use ascorbic acid, which the body absorbs as well as the vitamin C that occurs naturally in foods such as orange juice and broccoli.¹

Other forms include sodium ascorbate, calcium ascorbate and other mineral ascorbates, ascorbic acid with bioflavonoids, and combination products. Research has not shown that any form is better than another.^1,2

One study found no difference in blood levels or urine output between ascorbic acid, ascorbic acid with bioflavonoids and a calcium ascorbate blend, and its authors concluded that plain, low-cost ascorbic acid is the preferred source.¹

What's in ours

What’s in ours

Men's Multi: Vitamin C, 150 mg per serving, from the label
Immune Support: Vitamin C, 180 mg per serving, from the label

Side effects, medicines, and who should ask first

High doses can cause diarrhea, nausea, stomach cramps and other gut upset, because vitamin C that is not absorbed draws water into the gut.^1,2

The upper limit for adults is 2,000 mg a day from food and supplements combined, including during pregnancy and breastfeeding. It is 1,800 mg for teens aged 14 to 18 and lower for children. It does not apply to people given vitamin C as medical treatment by a doctor.^1,2

High intakes raise the oxalate and uric acid passed in urine, which could add to kidney stones, especially in people with kidney problems. Studies conflict, and NIH says the best evidence of a link is in people who already pass too much oxalate.^1,5

In people with hereditary hemochromatosis, high doses taken for a long time could worsen iron overload and damage tissues. NIH says people with this condition should avoid vitamin C supplements.^1,8

Ask your pharmacist or doctor first

Prescribing labels for extended-release mixed amphetamine salts name ascorbic acid, which is vitamin C, as an example of an acidifying agent that lowers blood levels of amphetamine and can make it less effective. Tell your prescriber if you take vitamin C.^11,12

On the medicine's label

Ask your pharmacist or doctor first

Vitamin C taken at the same time as levothyroxine might increase how much of the medicine is absorbed.⁴

Reported in studies

Your doctor may want to check on you

In one study, vitamin C taken with other antioxidants such as vitamin E, selenium and beta-carotene blunted the rise in HDL cholesterol from simvastatin taken with niacin. It is not known whether this happens with other cholesterol medicines, and NIH says doctors should check cholesterol levels in people taking both.^1,2

Reported in studies

NIH also says vitamin C and other antioxidant supplements might interact with chemotherapy and radiation therapy. Anyone having cancer treatment should check with their oncologist first.^1,2

Ask first if you have hemochromatosis, have had kidney stones or have kidney disease
Ask first if you take levothyroxine, a statin or an amphetamine medicine for ADHD
Ask first if you use a blood glucose meter, because high intakes might cause false readings⁴
Ask first if you are pregnant or nursing

Questions people ask

Does vitamin C do anything for skin?

Your skin needs it to make collagen, and normal skin holds high levels of it. Whether extra vitamin C changes how skin looks in someone who already gets enough has not been shown. In one small trial, 180 mg a day raised a laboratory measure of the skin's antioxidant activity within weeks.^6,10

Is it better to get vitamin C from food or a supplement?

Most people in the United States get enough from food and drink. The ascorbic acid in supplements is absorbed as well as the vitamin C in food, so a supplement is a reasonable way to fill a gap for people who smoke or eat a narrow range of foods.^1,2

Do men need more vitamin C than women?

A little more. The recommended amount is 90 mg a day for men and 75 mg for women, and smokers of either sex need 35 mg more. In a national survey, men took in about 105 mg a day from food and drink and women about 84 mg.^1,2

Can you take too much vitamin C?

Yes. Adults should stay under 2,000 mg a day from all sources. High doses commonly cause diarrhea, nausea and cramps, and people with hemochromatosis or a history of kidney stones should ask a doctor before taking large amounts.^1,2

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See the Full Measure line Immune Support Men's Multi

Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.