Naka Nutri B12 - 5000 mcg - Fast-acting sublingual methylcobalamin liquid for better absorption. Vitamin B12 is essential for the manufacture of red blood cells, is necessary for energy production, and helps support the normal function of nerve cells. If you follow a vegetarian or vegan diet, you may have a B12 deficiency as it is derived solely from animal foods and their sources. If you are over the age of 50, your natural stores of vitamin B12 are also depleted.