Vitamin B₁ works as a coenzyme in some types of metabolism, such as glycolysis and the citric acid cycle, which means it is deeply involved in energy production. Notably, vitamin B₁ controls the activity of pyruvate dehydrogenase, an enzyme involved in sugar metabolism, thus vitamin B₁ deficiency makes it harder to turn sugars into energy. Pork, whole grains, fish eggs, and eel are all rich in vitamin B₁.