Simplify the following text for a Grade 7 native English-speaking person.
Original: Christiaan Eijkman ( ; 11 August 1858 , Nijkerk , Gelderland -- 5 November 1930 , Utrecht ) was a Dutch physician and professor of physiology whose demonstration that Beriberi is caused by poor diet led to the discovery of vitamins .
Simplified: Christiaan Eijkman ( August 11 , 1858 - November 5 , 1930 ) was a Dutch doctor .