Most adults need 75 to 90 mg of vitamin C per day, an amount easily covered by diet alone. If you’re supplementing, doses in the 200 to 500 mg range hit the sweet spot for absorption and safety, while anything above 1,000 mg offers diminishing returns and raises the risk of side effects.
The right amount for you depends on your sex, whether you smoke, and what you’re hoping the supplement will do. Here’s how to sort through it.
The Official Daily Recommendations
The current recommended dietary allowance (RDA) for vitamin C is 90 mg per day for adult men and 75 mg per day for adult women. These numbers represent the amount needed to prevent deficiency and maintain normal function in most healthy people. If you’re pregnant, the target rises to 85 mg per day, and if you’re breastfeeding, it’s 120 mg per day. Breastfeeding women appear to need about 36 mg more daily than non-breastfeeding women just to maintain comparable blood levels, since the vitamin passes into breast milk.
Smokers need an extra 35 mg per day on top of the standard recommendation, bringing their target to at least 125 mg for men and 110 mg for women. Smoking accelerates the breakdown of vitamin C in the body and is consistently linked to lower blood levels of the vitamin, even when intake is similar to nonsmokers. Research on pregnant and breastfeeding women confirms this pattern: smoking was associated with significantly lower vitamin C levels regardless of intake.
Why More Isn’t Always Better
Your body absorbs vitamin C very efficiently at lower doses. Between 30 and 180 mg per day, you absorb roughly 70% to 90% of what you take. Once you push past 1,000 mg (1 gram) in a single dose, absorption drops below 50%. The excess gets filtered out by your kidneys and excreted in urine, which is the origin of the old joke about expensive vitamin supplements just creating expensive urine.
This absorption curve is the main reason many nutrition researchers suggest a supplement in the 200 to 500 mg range if you want to top off your levels. At 200 mg, your tissues are close to fully saturated. Doubling or tripling that dose doesn’t meaningfully increase how much vitamin C is circulating in your blood.
What the Cold Research Actually Shows
The most studied reason people reach for vitamin C supplements is the common cold. The evidence is more nuanced than most people expect. Taking vitamin C regularly (at least 200 mg per day) shortens the average cold by about 9.4%, which works out to roughly a day less of symptoms for a bad cold. It also reduces the severity of symptoms by about 15%.
The effect is more noticeable for serious symptoms than mild ones. In a large trial with Swedish schoolchildren, regular vitamin C use cut school absences during colds by 18%. A Canadian trial in adults found a 21% reduction in days people were stuck at home sick. So while vitamin C won’t prevent you from catching a cold, consistent daily use does appear to make colds shorter and less disruptive.
The key word is “regular.” Starting vitamin C after symptoms appear has not shown the same benefit in most trials. If cold prevention is your goal, a modest daily dose of 200 to 500 mg is better supported than loading up with megadoses once you start sneezing.
Risks of High Doses
The tolerable upper intake level for adults is set at 2,000 mg per day. Going above that reliably causes digestive problems, most commonly nausea, diarrhea, and stomach cramps. These happen because unabsorbed vitamin C draws water into your intestines.
A more serious concern, particularly for men, is kidney stones. Your body converts some vitamin C into oxalate, which is excreted through urine. At 2 grams per day, urinary oxalate excretion jumps by about 22%, and oxalate is a key ingredient in the most common type of kidney stone. A large study found that men taking 1,000 mg or more of supplemental vitamin C per day had a 43% higher risk of developing kidney stones compared to men taking less than 90 mg. The risk became statistically significant at total intakes around 700 to 800 mg per day. A separate Swedish study of over 23,000 men found that supplemental vitamin C nearly doubled the risk of stones. Interestingly, this association was not found in women.
If you’re a man with a history of kidney stones, keeping your supplement dose below 500 mg per day is a reasonable precaution.
Choosing a Supplement Form
Standard ascorbic acid tablets are the cheapest and most widely available form, and they work well for most people. Mineral ascorbates (sometimes labeled “buffered vitamin C”) combine vitamin C with calcium or sodium, which can be gentler on the stomach if plain ascorbic acid causes discomfort.
Liposomal vitamin C, which wraps the vitamin in tiny fat particles, has gained popularity as a premium option. A scoping review of 10 studies found that 9 of them showed higher blood levels from liposomal formulations compared to standard vitamin C, with peak levels ranging from 1.2 to 5.4 times higher. However, context matters: in people who already had adequate vitamin C levels at the start of the study, the difference shrank to just 1.3 to 1.4 times higher. In other words, liposomal delivery offers the biggest advantage for people who are genuinely deficient. If your levels are already decent, a standard tablet gets you most of the way there at a fraction of the cost.
Interactions With Medications
High-dose vitamin C can interfere with the blood thinner warfarin. In one well-documented case, a patient taking vitamin C alongside warfarin couldn’t achieve proper blood thinning even at four times his normal warfarin dose. When vitamin C was stopped, his blood-thinning response surged to dangerously high levels within two days. If you take warfarin or similar anticoagulants, talk with your prescriber before adding vitamin C supplements.
Vitamin C also enhances iron absorption, which is helpful if you’re iron-deficient but potentially problematic if you have a condition that causes iron overload, such as hemochromatosis.
A Practical Dose for Most People
If you eat several servings of fruits and vegetables daily, you likely don’t need a vitamin C supplement at all. A single orange provides about 70 mg, a cup of strawberries about 85 mg, and a cup of broccoli around 80 mg. But if your diet is inconsistent, you smoke, or you want the modest cold-fighting benefit, a daily supplement of 200 to 500 mg covers your bases without wasting money on unabsorbed excess or raising your risk of side effects. Split doses (say, 250 mg twice a day) will keep blood levels steadier than one large dose, since your body can only absorb so much at once.