Why humans and guinea pigs share a strange biological vulnerability to scurvy

Nature · Published 29 September 2026 Swipe more like this →

In short: Most animals synthesize their own vitamin C, but humans, higher primates, and guinea pigs cannot. A genetic mutation rendered the necessary enzyme dysfunctional in our ancestors, making this essential nutrient a dietary requirement. Without it, we face scurvy, yet our bodies strictly limit how much we can actually absorb.

Vitamin C, or l-ascorbic acid, is a water-soluble nutrient vital for collagen formation, neurotransmitter production, and immune health. While most creatures produce it internally, humans and a select group of other species—including bats, some fish, and guinea pigs—must obtain it from plants. This dependency stems from an ancient genetic mutation that disabled the enzyme required for internal synthesis. Consequently, we rely on fruits and vegetables to prevent deficiency, a condition that historically led to the disease known as scurvy.

The body maintains vitamin C levels through a precise, energy-dependent transport system that keeps tissue concentrations significantly higher than those found in plasma. However, this system has a ceiling. Once plasma levels reach saturation—roughly 65 μmol/L—the body stops absorbing extra amounts. Consuming more than 200 mg daily does not increase tissue storage; instead, the kidneys excrete the excess in urine. This biological limit explains why megadosing often provides no physiological benefit and can even trigger gastrointestinal distress.

Beyond its role as an essential nutrient, vitamin C acts as a versatile chemical tool. It serves as a critical cofactor for enzymes involved in building collagen, which is necessary for maintaining cartilage and blood vessels. In food science, its ability to donate electrons makes it a powerful antioxidant, often added to products to prevent browning. Interestingly, while standard doses support health, researchers have found that at extremely high, non-physiological concentrations delivered intravenously, vitamin C can shift to act as a pro-oxidant, showing potential toxicity against cancer cells in experimental settings.

The scientific understanding of this molecule has evolved rapidly since its 1912 discovery. By 1933, it became the first vitamin to be chemically manufactured, a breakthrough that contributed to Albert Szent-Györgyi receiving the Nobel Prize in Physiology or Medicine in 1937. Today, while global health agencies provide varying intake recommendations, the challenge remains that vitamin C is highly labile. It degrades easily when exposed to light, heat, or oxygen, meaning that even a healthy diet can be depleted by cooking methods like boiling or frying.

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