Vitamin C and Scurvy
In a sea voyage that lasted from 1740 to 1744, George Anson lost 1300 of his 2000 crew, mostly to a disease called scurvy that had been known about since 1500BCE, where the Ebers scroll in Egypt described the diease and also described curing it with onions (a source of vitamin C). Hippocrates even wrote about it in the 4th century BCE. The cure for scurvy has been forgotten and rediscovered over and over.
The most obvious symptoms of scurvy are swollen gums, fatigue, pain in the limbs caused by internal bleeding, red-blue spots on the skin, shortness of breath, bruising.
swollen gums are one symptom of scurvy
In 1747, 3 years after Anson's voyage, the Scottish physician James Lind showed through clinical trial that scurvy could be curved using citrus fruits, but his results were buried as a short paragraph in a very long and complicated treatise, which was completely ignored for about 40 years.
The established medical professionals ignored the idea that citrus fruits might cure scurvy because the idea flew in the face of the current knowledge of that time. This is the same kind of blindness that Semmelweiss was to experience 100 years later when trying to introduce the idea of cleaning your hands to surgeons. Scurvy at the time was thought to be caused by a kind of "internal putrefaction", and it was not believed that the anecdotes of sailors could somehow be more correct than the knowledge of physicians.
In 1794, Commander Peter Rainier set sail for India on the HMS Suffolk. In an experiment suggested by Rear Admiral Gardner, the ship had on board lemon juice and sugar, instead of the usually recommended malt and wort. The voyage took 23 weeks, and not one person contracted scurvy.
As soon as this news arrived back in England (1795), there was an upswelling of support for using lemon juice which forced the Sick And Hurt Board to change its recommendations.
It wasn't until 1932 that the essential vitamin C was isolated from citrus fruits, but it was obvious that there was something in them that was stopping scurvy.