Vitamins B-6 and B-12 are two of the B vitamins that have major roles in energy conversions. They pull energy out of carbohydrates, proteins and fats during digestion. These vitamins are also important for lowering your homocysteine level -- a form of an amino acid -- which has been tied with a possible reduction in risk of stroke and heart disease, the Harvard School of Public Health reports. Since B-6 and B-12 often work as a team, it’s perfectly safe to take them at the same time.
The Food and Nutrition Board of the Institute of Medicine recommends taking 1.3 milligrams of B-6 and 2.4 micrograms of B-12 each day for all healthy adults. You might need slightly different amounts if you're older, pregnant or nursing though. Many nutrients can be dangerous in high doses, so they have set tolerable upper intake levels. For vitamin B-6, you shouldn’t take more than 100 milligrams a day. Too much B-6 can affect your senses, as your neurological functions suffer. However, negative side effects generally stem from large-dose supplements, not from food. Vitamin B-12 isn’t known to cause adverse effects, even from high doses, thus a tolerable upper intake level has not been established.