Scurvy is caused by the absence of vitamin C in the diet. The human body cannot synthesize vitamin C; it must be consumed. Without it, the body cannot produce collagen properly, and collagen is a structural protein found in skin, blood vessel walls, cartilage, and other connective tissues. The consequence of scurvy is a progressive deterioration of everything connective tissue holds together: bleeding gums, joint pain, skin lesions, weakness, and eventually death.
Historical sailors who developed scurvy were eating predominantly preserved foods — salted meat, hardtack, dried legumes — that had been processed in ways that destroyed or significantly reduced their vitamin C content. The connection between fresh citrus fruit and scurvy prevention was established empirically long before the mechanism was understood; the British Navy’s requirement for lime juice on long voyages earned British sailors the nickname “limeys” and largely solved the problem for that fleet.
The critical difference between preserved meat and fresh meat in terms of vitamin C content is not widely known to the general public but is well established in nutritional science. Fresh meat — particularly organ meat such as liver — contains meaningful amounts of vitamin C, because the animal’s own biochemistry maintains the vitamin in its tissues up to the point of death. Cooked meat loses some of this vitamin C through heat degradation. Raw meat retains it.
Claude Piantadosi of Duke University, commenting on Alvarenga’s survival, identified the specific reason he was unlikely to develop scurvy: birds and turtles synthesize their own vitamin C, which means their flesh — and particularly their liver — contains enough of the vitamin to supply a human’s needs. Alvarenga was eating these animals raw, immediately after killing them, with no processing that would degrade the vitamin content. The diet that seemed most exotic and most extreme — raw turtle and raw bird — was, from the perspective of vitamin C nutrition, the diet most likely to prevent scurvy.