2. B Vitamins The B vitamin complex—including B1 (thiamine), B2 (riboflavin), B3 (niacin), B6 (pyridoxine), B12 (cobalamin), and folic acid—supports energy metabolism, brain function, and red blood cell production. Good sources include whole grains and meats. In homemade diets, you may need to add a B-complex supplement, especially if your dog is on a primarily vegetarian diet.