Vitamin C: what it does and which foods have it

What it does

Vitamin C is required for the biosynthesis of collagen, L-carnitine, and certain neurotransmitters; vitamin C is also involved in protein metabolism. (NIH) It also improves the absorption of nonheme iron, the form of iron in plant foods.

Where you find it in food

Fruits and vegetables are the best sources of vitamin C. (NIH)

Amounts are from the NIH Office of Dietary Supplements food table. "Servings to reach the daily value" is the daily value (90 mg) divided by the amount per serving.

How much you absorb

• Approximately 70% to 90% of vitamin C is absorbed at moderate intakes of 30 to 180 mg a day. (NIH)
• At doses above 1 gram a day, absorption falls to less than 50%, and absorbed vitamin C the body doesn't use leaves in urine. (NIH)

Food, and where an IV fits

Food comes first. Most people get what they need from a varied diet, and a nutrient in food comes with fiber, protein and everything else the food carries.

An IV takes a different route. It delivers a nutrient straight into the bloodstream, so none of it depends on absorption in the gut. For vitamin C, the difference is large: oral vitamin C, even in very large doses, can raise blood levels to about 220 micromoles per liter at most; IV administration can produce levels as high as 26,000 micromoles per liter. (NIH)

Vitamin C is in Immunity, Performance, Radiance and Rebuild, and is available as an add-in (ascorbic acid, $30). Tri-Immune, a $30 shot, also contains it.

Who tends to run low

The NIH lists these groups among those more likely to fall short:

• People who smoke and those exposed to secondhand smoke
• People with limited food variety
• People with malabsorption and certain chronic diseases

A lab panel ordered by your provider can show your own levels. See lab testing before IV therapy.

More from our notes

The body needs it to make collagen. It helps the immune system work properly, acts as an antioxidant that helps protect cells from free-radical damage, and improves absorption of iron from plant foods.

The National Cancer Institute states that people with G6PD deficiency should not be given high doses because of the risk of hemolysis, that people likely to form kidney stones should not receive IV vitamin C, that kidney failure has been reported after IV vitamin C in people with a history of kidney disease, and that high doses are not recommended in hemochromatosis.

Good to know

High-dose IV vitamin C is not appropriate for everyone, including people with G6PD deficiency, kidney disease or a history of kidney stones, which is why your provider decides. (National Cancer Institute)