Anyone at any age, can become B12 deficient. However, certain people are at an elevated risk. They include the following:
Vegetarians, vegans and people eating macrobiotic diets.
People aged sixty and over
People who’ve undergone any gastric and/or intestinal surgery, including bariatric surgery for weight loss purposes (Gastric bypass).
People who regularly use proton-pump- inhibitors. H2 blockers, antacids, Metformin, and related diabetes drugs, or other medications that can interfere with B12 absorption.
People who undergo surgeries or dental procedures involving nitrous oxide, or who use the drug recreationally.
People with a history of eating disorders (anorexia or bulimia).
People with a history of alcoholism.
People with a family history of pernicious anaemia.
People diagnosed with anaemia (including iron deficiency anaemia, sickle cell anaemia and thalassaemia).
People with Crohn’s disease, irritable bowel syndrome, gluten enteropathy (celiac disease), or any other disease or infection like h pylori that cause malabsorption of nutrients.
People with autoimmune disorders (especially thyroid disorders such as Hashimoto’s thyroiditis and Grave’s disease) Type 1 diabetes, vitiligo, lupus, Addison’s disease, ulcerative colitis, infertility, acquired agammaglobulinemia, or a family history of these disorders.
Apart from Thyroid problems which you have ruled out do you see yourself among any of the above people?
Symptoms of B12 deficiency tend to develop slowly and may not be recognised immediately. As the condition worsens, common symptoms include:
Weakness and fatigue
Light-headedness and dizziness
Palpitations and rapid heartbeat
Shortness of breath
A sore tongue that has a red, beefy appearance
Nausea or poor appetite
Weight loss
Diarrhoea
Yellowish tinge to the skin and eyes
If low levels of B12 remain for a long time, the condition also can lead to irreversible damage to nerve cells, which can cause the following symptoms:
Numbness and tingling in the hands and feet
Difficulty walking
Muscle weakness
Irritability
Memory loss
Dementia
Depression
Psychosis It is also important that your Folate level is monitored as this is essential to process the B12.
There is a complex interaction between folic acid, vitamin B12 and iron. A deficiency of one may be "masked" by excess of another so the three must always be in balance.
Symptoms of a folate deficiency can include:
symptoms related to anaemia
reduced sense of taste
diarrhoea
numbness and tingling in the feet and hands
muscle weakness
depression
Folic acid works closely with vitamin B12 in making red blood cells and helps iron function properly in the body.
The British Society for Haematology guidelines say on the Diagnosis of B12 and Folate Deficiency "I the presence of discordance between the test result and strong clinical features of deficiency, treatment should not be delayed to avoid neurological impairment".https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjcg4_zw-zUAhWTHsAKHVU2AC4QFggkMAA&url=http%3A%2F%2Fwww.b-s-h.org.uk%2Fguidelines%2Fguidelines%2Fdiagnosis-of-b12-and-folate-deficiency%2F&usg=AFQjCNHIwY0LNaLa7ByDGyaCYpwKX4kwhg
Make a list of your symptoms and present this to your doctor and ask him to treat you according to your symptoms and (perhaps) even start you on loading doses "until there is no further improvement" according to the N.I.C.E guidelines below. Click on the link, then on "Scenario: Management" and scroll down to "Treatment for B12 deficiency"
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&uact=8&ved=0ahUKEwjJwpuVwuzUAhWTOsAKHXj8B3sQFgg9MAc&url=https%3A%2F%2Fcks.nice.org.uk%2Fanaemia-b12-and-folate-deficiency&usg=AFQjCNFje3rEICwABYJ6ZJS4D-nMto5QTw
If possible take someone with you who can validate your neurological symptoms as the doctor is less likely to pooh pooh you in front of a witness.I am not a medically trained person but I've had P.A. (a form of B12 deficiency) for more than 45 years.
I wish you well.