There are three enzymes involved in glucose metabolism that are thiamin dependent, a-ketoglutarate dehydrogenase, pyruvate dehydrogenase, and transketolase. So it stands to reason that thiamin may help with glucose tolerance. A number of studies have shown fiber to help with glucose tolerance (Archives of Internal Medicine [2007; 167(21): 2304-9], to name one of many). A study published in Diabeologia (1998;41:1168-1175) looked at glucose tolerance in nearly 2200 non-diabetic men and women between the ages of 50 and 75. Researchers noted that there was an inverse association between fiber intake and fasting glucose. Fiber intake was also associated with lower glucose two hours into a glucose tolerance test. Adjusting for the lower fasting glucose level existing with high fiber intake negated the glucose lowering effect at two hours post prandial. Thiamin intake was associated with lower glucose at two hours; this lowering effect was independent of fiber intake or fasting glucose levels.
Another study published in the Journal of Gastroenterology and Hepatology (1991;6:59-60), demonstrated that thiamin helped the glucose tolerance curves in patients with cirrhosis. Thiamin is stored, to a certain extent, in the liver. It is also metabolized there.
Thiamin also improves the function of the vascular endothelium. A study published in the Annals of Vascular Surgery (2006; 20(5): 653-8). The study looked at 10 patients with diabetes, 10 patients with impaired glucose tolerance and 10 healthy patients. It found that giving 100 mg of thiamin intravenously improved vessel elasticity and that thiamin may be useful in improving atherosclerosis in patients with type 2 diabetes.