Health Reference LibraryHow much vitamin C should I take, and how much is too much?
This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.
Summary
Food covers the 40 mg reference intake for anyone eating fruit and vegetables, so a supplement is about extra, and 500 to 1000 mg a day is the range most trials used. Blood levels saturate at around 200 mg a day; above that the gut absorbs a smaller share and the kidneys pass the rest, which is why splitting a dose in two works better than one large one. The NHS says 1000 mg a day or less is unlikely to cause harm. Above that, stomach pain, diarrhoea and wind are common, and anyone who has had kidney stones should stay well below it.
Dose calculator: capsules to reach your vitamin C target
Enter the daily amount of vitamin C you are aiming for and see how many servings of each Nutri Tailor product reach it. Nothing you enter leaves this device. No AI is used.
This tool does arithmetic on the label figures. It is not personal dosing advice and it knows nothing about your history or blood results. The reference intake, the safe upper guide and the trial doses are on this page; talk to your GP or a registered nutritional therapist before changing what you take.
Effective dose
The reference intake is 40 mg a day for adults, which one orange or half a red pepper covers. Food covers the reference intake for anyone eating fruit and vegetables, so the supplement question is about extra. 200 mg a day saturates the blood in the absorption studies; beyond that the gut takes up a smaller and smaller share and the kidneys pass the rest. 500 to 1000 mg a day is the range most supplement trials used, and 1000 mg is the sensible ceiling. Splitting a large dose into two halves absorbs more than one big dose.
Safety profile
How much is too much: the NHS says 1000 mg or less a day from supplements is unlikely to cause harm; above that, stomach pain, diarrhoea and wind are common. Above about 1000 mg a day the unabsorbed vitamin C pulls water into the bowel, which is the stomach pain and loose stools people report, and long term high doses raise oxalate in the urine, which matters for anyone who has had kidney stones. Very high intakes also raise iron absorption, a problem only for people with iron overload. Buffered forms such as magnesium ascorbate are gentler on the stomach at the same dose.
Guideline positions
NHS vitamins and minerals guidance for vitamin C. NIH Office of Dietary Supplements fact sheet for vitamin C where one exists. The trial doses quoted above are from the sources listed on this page.
Practical framework
Capsules to reach the dose, from the Nutri Tailor range, all made in the UK: [vitamin C ascorbic acid powder](/products/vitamin-c-ascorbic-acid-powder), 1000 mg per scoop, so half a scoop twice a day is 1000 mg split; [magnesium ascorbate capsules](/products/magnesium-ascorbate), 485 mg of buffered vitamin C with 36 mg of magnesium per capsule. To read your own result against the UK ranges, use the free blood test result interpreter. This is a summary of published research, not personal health advice. Talk to your GP or a registered nutritional therapist before changing what you take, especially if you are pregnant, have a diagnosed condition or are under ongoing care.
Common misconceptions
That more vitamin C works faster: above the doses the trials used there is no extra effect, only more side effects. That the front of the bottle states the dose: read the per capsule figure and the serving size on the back. That the NHS figure is a toxic threshold: it is the level below which harm is unlikely, which is a different thing.
Sources
- NHS 2024. Vitamins and minerals: Vitamin C. NHS.
- NIH Office of Dietary Supplements 2026. Vitamin C Consumer Fact Sheet. NIH ODS.