Vitamin B1 molecule. Computer model showing the structure of a molecule of vitamin B1 (thiamine). Vitamin B1 is an essential nutrient that humans are unable to produce and need to obtain from their diet. It is important for the normal function of the heart, muscles and nervous system, as well as normal growth and development. Deficiency can lead to the disease beriberi, which causes weight loss, emotional disturbances, and limb pain and weakness. Atoms are represented as colour-coded spheres: carbon (black), hydrogen (white), nitrogen (blue), oxygen (red), and sulphur (yellow).