Secondary thiamin deficiency is caused by Increased demand (eg, due to hyperthyroidism, pregnancy, lactation, strenuous exercise, or fever) Impaired absorption (eg, due to prolonged diarrhea) Impaired metabolism (eg, due to hepatic insufficiency) In people with alcohol use disorder, many mechanisms contribute to thiamin deficiency; they include decreased intake, impaired absorption and use, increased demand, and possibly an apoenzyme defect.