Vitamin B12 deficiency occurs when the body does not get enough of this essential nutrient, which is crucial for producing red blood cells and maintaining a healthy nervous system. It can lead to symptoms such as fatigue, weakness, and neurological issues like numbness or tingling in the hands and feet. This deficiency is often seen in individuals with certain dietary restrictions, such as vegetarians and vegans, since Vitamin B12 is primarily found in animal products. Additionally, some medical conditions can affect absorption, making it important for at-risk individuals to monitor their levels and consider supplementation if necessary.