Book for my PE507 class says (incidental that I was just reading this chapter tonight)...
Thiamine - Serves as a coenzyme for energy production from carbohydrate; essential for normal functioning of the central nervous system
Riboflavin - Functions as a coenzyme involved in the energy production from carbohydrates and fats; maintenance of healthy skin
Niacin - Functions as a coenzyme for the aerobic and anaerobic production of energy from carbohydrate; helps synthesize fat and blocks release of free fatty acids; needed for healthy skin.
These are all water soluble so your body won't store them up and if you binge you'll just excrete the extra. The only one you can really go to high on is Niacin. Thiamine and Niacin can be gotten from whole grains. Riboflavin from leafy greens. All three from beans and enriched grain products.
Enzymes in your body help regulate the diverse chemical reactions that happen. Coenzymes, like these three, form half of an enzyme.
If those bagels you eat are enriched with these three I'm guessing you don't need to worry about them