Vitamin C: Oral vs. Intravenous, Immune Effects, Cancer, Exercise Adaptation & More

Cooking and exposure to oxygen can destroy 25% or more of the vitamin C in foods, so it's best to eat vitamin C-rich foods raw and immediately after cutting or peeling.

Meat is a very poor source of vitamin C. In fact, of more than 950 beef items listed in the USDA's food and nutrition database, only 21 items contain any vitamin C at all, and most contain tiny amounts that would be lost in cooking.

"A higher dose of vitamin C supplementation is more effective against colds in children under 16 compared to adults. In adults, cold duration decreased 21% with 2 grams daily and 6% with just 1 gram daily. In children, cold duration decreased 26% with 2 grams of vitamin C daily and 17% with 1 gram daily.

Studies show that frequent moderate to vigorous acute exercise sessions lasting about an hour can boost the body's immune system, but repeated high-intensity training or competition in endurance activities, such as long distance running, can actually diminish it.

A person's peak plasma vitamin C concentration won't exceed 220 micromoles per liter from oral vitamin C intake—even if they take a maximum oral dose of 3 grams, 6 times daily. By contrast, intravenous vitamin C can produce plasma concentrations as high as 15,000 micromoles per liter.

The bioavailability of intravenous vitamin C is a lot higher than oral vitamin C, potentially reaching blood concentrations that are 30-70x higher than can be achieved orally.

Vitamin C might lead to kidney stones in patients with pre-existing kidney impairments, but vitamin C poses a relatively low risk of developing kidney stones in most healthy people.

The maximum plasma vitamin C concentration from intravenous vitamin C can be as high as 15,000 micromoles per liter, which is 68x higher than can be achieved through oral consumption.

The recommended dietary allowance [of vitamin C] for healthy men is 90 milligrams per day; for women, it's 75 milligrams per day.

Vitamin C's bioavailability maxes out at about 200 milligrams when given as a single dose. At 500 milligrams, the bioavailability decreases, and excess vitamin C gets excreted in the urine.

A few studies suggest that oral bioavailability of vitamin C can be increased when consumed in liposomal form but only in doses higher than 5 grams.

One of the contributors to male infertility is excess reactive oxygen species. Evidence suggests that vitamin C decreases reactive oxygen species and increases fertility due to its antioxidant activity.

Given that vitamin C is essential for the synthesis of carnitine, which plays an important role in the utilization of fatty acids as energy, it's possible that low Vitamin C levels contribute to increased fat storage.

Multiple studies suggest that high-dose intravenous vitamin C can assist in cancer cell death primarily due to the formation of hydrogen peroxide.

Most animals can synthesize their own vitamin C, but humans can't—we have to get it from our diet or through supplements.