How do we find vitamin B12 deficiency?
There is the simplest way to catch up with vitamin B12 deficiency. When cobalamine levels are low, our bodies send signals to the face.

1. Nerve pain: Studies have shown that neuralgia may appear on the face when vitamin B12 is insufficient. There are various patterns, but pain is usually felt on only one side of the face. Dull pain may occur near the cheekbones just below the eyes, and sharp pain may be felt across the forehead. In severe cases, the pain comes down to the nose.
2.  Jaundice: Jaundice can cause the face to turn yellow, but it can also cause jaundice, which causes yellow eyes. Red blood cells are poorly made due to a lack of vitamin B12. Malignant anemia may occur simultaneously due to a lack of red blood cells. Symptoms of malignant anemia are diarrhea, including jaundice and loss of appetite.

Symptoms
Vitamin B acts as a crucial co-enzyme in the body. Vitamin B12, as knwon as cobalamine, is necessary for various bodily functions, like producing red blood cells, proper nerve function, and DNA synthesis. This vitamin B12 deficiency can lead to many health issues, and here are some potential consequences of its deficiency.

1. Anemia: Here comes anemia, definitely. Vitamin B12 is one of the B groups. It is a water-soluble vitamin used in various places such as red blood cell formation, cell metabolism, nerve formation, and DNA formation. Lack of vitamin B12 results in difficulty in forming normal red blood cells due to DNA synthesis disorders, which can lead to anemia. This vitamin B12 deficiency anemia is also called megaloblastic anemia because blood tests characterize abnormally large red blood cells compared to the norm. Symptoms may include fatigue, weakness, pale skin, and shortness of breath.
2. Neurological Symptoms: Numbness in the hands and feet, difficulty walking and balance, malfunction in memory, and cognitive difficulties. These are all linked to vitamin B12 deficiency, which sometimes causes irreversible nerve damage. Neurological problems could be myelopathy, peripheral, optic, and even dementia. This cobalamin deficiency is widespread in the elderly and after gastric surgery (1).
3.  Gastrointestinal Issues: A lack of vitamin B12 can cause loss of appetite, weight loss, constipation, diarrhea, and red tongue. Several small intestine disorders, especially if the ileum is involved (2), can interfere with cobalamine absorption. These conditions could include IBD, radiation enteritis, lymphoma, and so on. If you are already experiencing these conditions, your vitamin B12 levels should be appropriately monitored.
4. Bone Health: Vitamin B12 deficiency may be associated with an increased risk of osteoporosis and bone fractures.
5. Pregnancy Complications: Pregnant women with B12 deficiency may be at risk of giving birth prematurely or having a baby with low birth weight. This can also affect the neurological development of the fetus.

Where is the vitamin B12?
The optimal functioning of the central and peripheral nervous system depends on a constant supply of appropriate nutrients. Vitamin B12 is often found in meat such as beef and pork and animal foods such as eggs, milk, and salmon. In particular, meat from ruminants (containing between 0.36 and 4.43 µg of B12) and liver are valuable sources of the vitamin (3).
Milk and dairy products have slightly lower vitamin B12 amounts than meat. If the meat and milk were processed in thermal treatment, severe losses of vitamins are inevitable. However, cooked meat offers similar or even higher B12 portions compared to raw meat. Unlike other water-soluble vitamins, vitamin B12 is stored in a significant amount in the liver, so a lack of intake of food does not immediately lead to deficiency symptoms.

References
1) Giacomo Marchi,1,* Fabiana Busti,corresponding author1,* Acaynne Lira Zidanes,1 Alice Vianello,1 and Domenico Girelli1. Cobalamin Deficiency in the Elderly. Mediterr J Hematol Infect Dis. 2020; 12(1): e2020043.
2) Neeraj Kumar. Chapter 60 – Neurologic aspects of cobalamin (B12) deficiency. Handbook of Clinical Neurology. Volume 120, 2014, Pages 915-926.
3) Doreen Gille, Alexandra Schmid. Vitamin B12 in meat and dairy products. Nutrition Reviews, Volume 73, Issue 2, February 2015, Pages 106–115.