Most dietary deficiency of thiamine is the result of poor dietary intake. Thiamine requirement increases in excessive intake of:

Primary food sources for thiamine include yeast, organ meat, pork, legumes, beef, whole grains, and nuts. Milled rice and grains contain little thiamine, if any. Thiamine deficiency is therefore more common in cultures that rely heavily on a rice-based diet. Tea, coffee (regular and decaffeinated), raw fish, and shellfish contain thiaminases, which can destroy the vitamine. Thus, drinking large amounts of tea or coffee can theoretically lower thiamine body stores. Ref: Russell R.M., Suter P.M. (2012). Chapter 74. Vitamin and Trace Mineral Deficiency and Excess. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.