​Vitamin C loading during cold and flu season: How much is useful and when it becomes risky

When cold strikes in, vitamin C becomes a go-to supplement for many. Some start loading up oranges, some turn towards supplements. Even if vitamin C is important for the immune system, does taking heavy doses possess a risk? Here’s a closer look at how too much vitamin C can be risky, its impact on health, and what is the optimal amount to take.

While vitamin C may not be a cure-all solution for cold or flu, it can significantly shorten the duration. According to ResearchGate, regular consumption of vitamin C is linked to 8% reduction in the cold duration for adults. And the symptoms are slightly less severe.
As per NIH, the recommended dietary intake for vitamin C is 90 to 120 mg for adults. People who smoke require 35 mg more vitamin C per day than those who do not smoke.
Sources show regular vitamin C intake of ~200–500 mg/day supports immune health and modestly reduces cold duration, with doses above ~500–1,000 mg/day offering little additional benefit due to saturation of absorption and increased excretion.

Food sources of vitamin C are generally considered the safest options. Partly because food sources have other essential nutrients like fiber etc.
Some food sources of vitamin C are: bell peppers, broccoli, and strawberries.
On the other hand, vitamin C supplements, which include pills and powders can be risky. Supplements offer convenience, but they also make it easy to exceed safe limits.
Dietary dosage above 1000 mg is the risky threshold as the body becomes unable to fully absorb the vitamin C

Water soluble nutrients like vitamin C are excreted through the urine when consumed in excess amounts. And this is where the risk arises, as before excretion, vitamin C gets partially metabolised into oxalate. When oxalates are combined with calcium in the urine, a compound called calcium oxalate is formed, which is the most common type of kidney stone. In this manner, excess of vitamin C can be risky for the kidney.

Mayo Clinic recommends limiting to 2000 m of vitamin C a day. To avoid health risks doctors recommend:
Prioritising natural sources rather than supplements, and using supplements only when needed after doctors recommendation.
Proper hydration is also recommended as it helps in the dilution of oxalate in the urine, which can help reduce the formation of kidney stones.
Disclaimer: This article is for informational purposes only and should not be substituted for professional advice.