Back in 1912, Frederick Hopkins discovered that there were other substances in milk that rats needed to grow, and it wasn’t just the usual suspects like carbs, proteins, and fats.
By 1913, one of these substances was independently discovered by two different groups of scientists. Elmer McCollum and Marguerite Davis at the University of Wisconsin–Madison, and Lafayette Mendel and Thomas Burr Osborne at Yale University. McCollum and Davis received credit because they submitted their paper three weeks before Mendel and Osborne. The substances were called “fat-soluble” in 1918, and later “vitamin A” in 1920.