Not much, and not once the cold has started: NIH's NCCIH says taking vitamin C only after symptoms begin doesn't change how long or how bad the cold is. People who take it regularly may have slightly shorter or milder colds, and MedlinePlus puts the possible gain at about 8% shorter in adults and 14% in children, though it calls this not fully proven. For most people it doesn't prevent colds. MedlinePlus says more than 2,000 mg a day is not recommended, and the NHS says more than 1,000 mg a day can upset your stomach.
Does vitamin C work if I start it after I get sick?
This is the part most people miss. NCCIH, the NIH center that studies supplements, says plainly that taking vitamin C only after you start to feel cold symptoms doesn't affect the length or severity of the cold. MedlinePlus says the same: starting supplements after a cold begins doesn't appear to help.
So the big dose of fizzy tablets on day 1 of a sniffle is unlikely to change your week. Rest, fluids and symptom relief will do more for how you feel.
What about taking vitamin C every day?
NCCIH describes a review of 29 studies with more than 11,000 people. It found that regular vitamin C doesn't prevent colds in the general population and shortens colds only slightly.
MedlinePlus gives numbers for that small effect: large doses may make colds about 8% shorter in adults and 14% shorter in children. For a cold that lasts 7 days, 8% is roughly half a day. MedlinePlus also notes that results vary from person to person and the benefit is not fully proven.
- Started after symptoms: no effect on length or severity, per NCCIH
- Taken regularly, before you get sick: slightly shorter or milder colds
- Preventing colds: no, for most people
- Under short bursts of extreme physical stress: may cut the number of colds in half (see below)
Who might get more out of it?
One group stands out. NCCIH reports that in people exposed to short periods of extreme physical stress, such as marathon runners and skiers, taking vitamin C cut the number of colds in half. NCCIH's research summary for clinicians also names soldiers training in subarctic conditions as a group where it may be useful.
If you are training for a marathon or a similar intense event, regular vitamin C may be more worthwhile for you than for most people. It still won't treat a cold you already have.
How much is safe to take?
The amount adults need each day is small. MedlinePlus lists 90 mg a day for men and 75 mg for women, with 35 mg more if you smoke. The NHS sets its adult figure lower, at 40 mg a day. Good food sources include oranges and other citrus fruit, peppers, strawberries, broccoli, Brussels sprouts and potatoes.
MedlinePlus says amounts above 2,000 mg a day are not recommended. The NHS draws its line lower: more than 1,000 mg a day can cause stomach pain, diarrhea and gas, which go away once you stop the supplement. MedlinePlus also says high doses can, rarely, cause kidney stones. For the full breakdown, see how much vitamin C is too much.
Who should be careful with vitamin C supplements?
Check with a clinician or pharmacist before taking vitamin C supplements if any of these apply:
- Kidney disease: MedlinePlus says people with kidney disease should not take vitamin C supplements
- History of kidney stones: MedlinePlus lists kidney stones as a rare effect of high doses
- Hemochromatosis (iron overload): NCCIH says avoid high doses
- Cancer treatment or cholesterol medicine: NCCIH says talk to your care team first
- Pregnancy: large doses are not recommended, per MedlinePlus
When should you get care?
In an emergency, call 911Get care the same day if you or your child has trouble breathing or fast breathing, signs of dehydration, a fever lasting more than 4 days, or a chronic condition that is getting worse.
See a clinician if symptoms last more than 10 days without getting better, or if symptoms such as fever or cough improve and then come back or get worse.
If you are at higher risk for severe illness, CDC says to contact your clinician right away even if your illness is mild, and get tested if you think it could be flu or COVID-19.
Call 911 if someone is struggling to breathe, has blue or gray lips, has chest pain or pressure, is confused, or is hard to wake.
How our AI doctor decides when to send you to care ›What helps a cold more than vitamin C?
CDC's advice is simple: rest, drink plenty of fluids, and use saline nasal spray or drops. Honey can ease a cough in adults and children 1 year and older, but never give honey to a baby under 1. CDC also lists throat lozenges or cough drops, but don't give lozenges to children under 4.
Antibiotics don't work on colds, because colds are caused by viruses. CDC also says over-the-counter cough and cold medicines are not recommended for children under 6. Young children can have acetaminophen or ibuprofen for fever, but check the right dose with a clinician first.
Common questions
Does vitamin C help a cold?
Only a little, and mainly if you were already taking it regularly. NCCIH says starting vitamin C after symptoms begin doesn't change how long or how bad the cold is. MedlinePlus says large doses may make colds about 8% shorter in adults and 14% shorter in children, though this is not fully proven.
Does vitamin C prevent colds?
Not for most people. A large review of 29 studies found regular vitamin C didn't lower the number of colds in the general population. The exception is people under short bursts of extreme physical stress, like marathon runners, where colds were cut in half.
Is 1,000 mg of vitamin C too much?
It is under the 2,000 mg a day limit MedlinePlus gives, but it is more than 10 times what most adults need. The NHS says more than 1,000 mg a day can cause stomach pain, diarrhea and gas. Those symptoms go away when you stop.
Is orange juice as good as a supplement for a cold?
For getting your daily vitamin C, food is enough for most people, and MedlinePlus says a balanced diet almost always covers it. Neither juice nor a tablet started after the cold begins is likely to shorten it. Drinking plenty of fluids is part of CDC's cold advice.
Can I give my child vitamin C for a cold?
Vitamin C from fruit and vegetables is fine. Ask your pediatrician before giving supplements, since children need much smaller amounts: MedlinePlus lists 15 mg a day for ages 1 to 3 and 25 mg for ages 4 to 8. For a young child's cold, CDC recommends rest, fluids and saline drops, and no over-the-counter cough and cold medicine under age 6.
Can vitamin C cause kidney stones?
MedlinePlus says kidney stones are possible but rare at high doses. If you have had kidney stones or have kidney disease, talk to a clinician before taking vitamin C supplements.
Pymander is not a replacement for a physician and does not provide medical advice, diagnosis, or treatment. Always seek the advice of a qualified health provider with questions about a medical condition. If you think you may have a medical emergency, call 911.