vitamin B1 Any member of the group of 1,3-thiazolium cations that exhibit biological activity against vitamin B<small>₁</small> deficiency in animals. Symptoms of vitamin B<small>₁</small> deficiency include constipation, loss of apetite, fatigue, nausea, delirium, blurry vision and muscle weakness. Severe vitamin B<small>₁</small> deficiency can also lead to a disease known as <a href="https://en.wikipedia.org/wiki/Thiamine_deficiency" target="_blank">beriberi</a>. Vitamin B<small>₁</small> consists of the vitamer thiamin and its acid, aldehyde and phosphorylated derivatives (and their corresponding ionized, salt and hydrate forms). aminopyrimidine 1,3-thiazolium cation B vitamin