Vitamin B12 is crucial in the diet as it plays a key role in red blood cell formation, DNA synthesis, and maintaining healthy nerve cells. A deficiency can lead to anemia, fatigue, and neurological issues. It is primarily found in animal products like meat, dairy, and eggs, making it essential for individuals following a vegetarian or vegan diet to consider fortified foods or supplements. Adequate B12 intake is necessary to ensure optimal body function and support overall health.