There are three key enzymes involved in glucose metabolism that are thiamin-dependent: α-ketoglutarate dehydrogenase, pyruvate dehydrogenase, and transketolase. Because these enzymes play central roles in carbohydrate metabolism, it follows that thiamin status may influence glucose tolerance.
A number of studies have shown that dietary fiber improves glucose tolerance (for example, Archives of Internal Medicine 2007;167(21):2304–2309). One study published in Diabetologia (1998;41:1168–1175) examined glucose tolerance in nearly 2,200 non-diabetic men and women between the ages of 50 and 75.
The researchers observed an inverse association between fiber intake and fasting glucose levels. Higher fiber intake was also associated with lower glucose levels two hours into an oral glucose tolerance test. However, when the analysis was adjusted for the lower fasting glucose seen with higher fiber intake, the glucose-lowering effect at two hours post-challenge was no longer significant.
In contrast, thiamin intake was associated with lower glucose levels two hours after the glucose challenge, and this effect was independent of both fiber intake and fasting glucose levels.
Additional evidence comes from a study published in the Journal of Gastroenterology and Hepatology (1991;6:59–60), which found that thiamin improved glucose tolerance curves in patients with cirrhosis. This finding is biologically plausible, as thiamin is stored to some extent in the liver and is also metabolized there.
Thiamin has also been shown to influence vascular function. A study published in the Annals of Vascular Surgery (2006;20(5):653–658) evaluated 10 patients with type 2 diabetes, 10 patients with impaired glucose tolerance, and 10 healthy controls. Administration of 100 mg of thiamin intravenously improved vascular elasticity. The authors suggested that thiamin may play a role in improving endothelial function and atherosclerotic changes in patients with type 2 diabetes.
