Quest Thiamin 100mg Vitamin B1 ~ 50% Extra Free (60). Special offer with 90 tablets in total.. Quest Vitamin B1, also known as thiamin is a water-soluble vitamin that is required for the normal function of the nervous system.. Vitamin B1 is found in large quantities in the brain nervous tissue and can become depleted when large amounts of alcohol are consumed.. Vitamin B1 is needed for normal energy yielding metabolism where it helps to convert carbohydrates into fuel and is useful for those wishing to lose weight or those with diabetes.. Thiamin is also beneficial to heart health due to its role in energy production and neurotransmission.