Q: Deficiency of which vitamin may cause lactic acidosis?

Answer: Thiamine (Vitamin B1)

Clinically it may become significant in patients who have prolong NPO status or have TPN without essential vitamins in it. It should also be considered in patients who alcohol abuse and poor intake.

Severe lactic acidosis and thiamine deficiency during total parenteral nutrition--case report. Hepatogastroenterology. 2004 Jan-Feb;51(55):253-5.