Vitamin C Supplements: How Much You Actually Need (2026)

What to buy

Nature Made Vitamin C 500 mg is our pick. It is on USP’s public testing list, which checks contents and purity, and it costs $0.08 a day. One tablet is more than adults need.

Nature Made Vitamin C 500 mg
Our pick · USP Verified

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Want 1,000 mg? Nature Made’s 1,000 mg tablet is on the same testing list, for $0.16 a day.

Nature Made Vitamin C 1000 mg
1,000 mg · USP Verified

Check price on Amazon

Where to go next

Best vitamin C: the products we compared, ranked.
Vitamin C dosage guide: how much you need by age, with a calculator.
Vitamin C forms compared: plain, buffered, Ester-C and liposomal.
Third-party tested vitamin C: which products are on a public testing list.
What a day of vitamin C costs.

What vitamin C does

Vitamin C is a vitamin your body cannot make. It helps build collagen, heal wounds and absorb iron, and a real shortage causes scurvy (NIH). Here is what trials found when people took extra.

What trials found for each goal.
Goal	Evidence	What trials found
Colds	Small effect	In trials of 200 mg a day or more, regular use did not cut how often most people caught colds; it shortened them about 8% in adults (Hemilä 2013). Marathon runners, skiers and soldiers in the cold got half as many.
Blood pressure	Small effect	Short trials found systolic pressure about 3 to 4 points lower (Juraschek 2012). No long trial shows fewer heart problems.
Heart and cancer	Not shown	In 14,641 male doctors given 500 mg a day for about 8 years, heart attacks, strokes, cancer and deaths did not change (Sesso 2008).
Iron	Single meals only	It helps absorb iron from plant foods in one meal, but adding it to iron pills did not help adults with anemia (Li 2020).
Skin and wounds	Unclear	Skin holds a lot of vitamin C, but whether pills do more than a good diet is poorly understood (Pullar 2017).

Who may run low

NIH lists people who smoke or breathe secondhand smoke, people who eat a narrow range of foods, people with poor absorption or some long-term illnesses such as kidney disease on dialysis, and infants fed boiled or evaporated milk. Smokers need 35 mg more a day.

How long it takes

Vitamin C works on daily intake, not a single dose. The cold trials measured regular use through a season; starting it after a cold began had no consistent effect (Hemilä 2013). In NIH studies, blood levels rose with each step up in daily dose until they leveled off near 400 mg a day in women and 1,000 mg in men (Levine 1996; Levine 2001).

Is vitamin C safe?

At normal doses, yes. The adult upper limit is 2,000 mg a day; more often causes diarrhea and upset stomach (NIH). A few things to check:

Kidney stones or kidney disease: ask your doctor before any vitamin C supplement. In men, 1,000 mg or more a day from supplements came with a 19% higher stone risk (Ferraro 2016); women showed no link.
Cancer treatment: NIH says people getting chemotherapy or radiation should ask their oncologist first.
Hemochromatosis (iron overload): vitamin C raises iron absorption, so ask your doctor.
Children have lower limits: 400 to 1,200 mg a day by age (NIH).

Questions people ask

What did the Cochrane review find about vitamin C and colds?

Regular vitamin C did not cut how often most people caught colds, and shortened colds by about 8% in adults and 14% in children. Marathon runners, skiers and soldiers in the cold got half as many colds (Hemilä 2013).

What about starting vitamin C after cold symptoms begin?

The same Cochrane review found no consistent effect from starting vitamin C after a cold began (Hemilä 2013).

Does vitamin C affect iron absorption?

Yes, in a single meal: it helps the body absorb iron from plant foods (Lynch 1980). Over a whole diet the effect was much smaller (Cook 2001), and in adults taking iron pills for anemia, adding vitamin C did not help (Li 2020).

Is there any benefit to taking more than about 200mg a day?

Little for most people. In an NIH study of 7 healthy men, a 200 mg dose was fully absorbed and less of 500 mg and up (Levine 1996), and NIH says cells are saturated at about 100 mg a day. Trials that made colds about 15% less severe used 1,000 mg or more (Hemilä 2023).

Vitamin C Supplements: How Much You Actually Need & What to Buy