FactSentinel

Vitamin C is essential for normal immune function, but taking megadoses of it daily does not produce a permanent strengthening of the immune system. The body tightly regulates how much vitamin C it absorbs and retains. Once tissues are saturated, typically at intakes well below common megadose levels, any excess is simply excreted in urine rather than stored or used to enhance immune capacity. This means there is a ceiling beyond which more vitamin C provides no additional benefit, let alone a lasting one.

Decades of clinical research, including studies dating back to the work popularized by Linus Pauling in the 1970s, have failed to show that high-dose vitamin C prevents colds or infections in the general population. Some studies suggest modest reductions in the duration or severity of colds in specific groups, such as endurance athletes or people under extreme physical stress, but this is far from evidence of a permanent immune upgrade. The immune system does not work like a muscle that becomes stronger and stays that way after repeated exposure to a nutrient; it relies on a complex, dynamic balance of cells and signaling molecules that respond to actual threats, not stockpiled vitamins.

A common misconception is that if a small amount of a nutrient is beneficial, a much larger amount must be proportionally more beneficial. This is not how nutritional biochemistry works. Excessive vitamin C intake can also cause gastrointestinal discomfort and, in rare cases, kidney stones. Maintaining adequate vitamin C through a balanced diet supports normal immune function, but no supplement regimen creates permanent immunity enhancement.