Despite the pioneer work of James Lind and Nikolai Lunin, many vitamin deficiency states were still thought to be of infectious origin, even in the early 1900s.
Nikolai Lunin and the concept of vitamins
Vitamins are defined as a group of complex organic compounds present in minute amounts in natural foodstuff that are essential to normal metabolism and lack of which in the diet causes deficiency diseases. Vitamins are required in trace amounts (micrograms to milligrams per day) in the diet for health, growth and reproduction.