Vitamin B1, also known as thiamin, helps fuel your body by converting blood sugar into energy. It keeps your mucous membranes healthy & is essential for nervous system, cardiovascular & muscular function. Nutritionists categorise vitamins by the materials that a vitamin will dissolve in. There are two categories: water-soluble & fat-soluble vitamins. Water-soluble vitamins, which include the B-complex group & vitamin C, travel through the bloodstream. Whatever water-soluble vitamins are not used by the body are eliminated in urine, which means you need a continuous supply of them in your food. Vitamin B1 is a water-soluble vitamin.