This can be caused by stress, poor eating habits and digestion, or a diet low in animal protein (meat, fish, dairy)
Ofioliti 33:119 Behnam S, Ramazi H (2019) Interpretation of geomagnetic data using power spectrum and 3D modeling of Gol-e-Gohar magnetic anomaly

Chan School of Public Health: "Vitamin B12." Inflammatory Bowel Diseases: "Prevalence of and risk factors for vitamin B(12) deficiency in patients with Crohn's disease," "Vitamin B12 deficiency in inflammatory bowel disease: prevalence, risk factors, evaluation, and management." MedlinePlus: "Cyanocobalamin Injection." National Health Services: "Hydroxocobalamin," "Treatment -Vitamin B12 or folate deficiency anaemia Contents," "Vitamin B12." Nutrition Reviews: "How prevalent is vitamin B(12) deficiency among vegetarians?" Surgery for Obesity and Related Diseases: "Vitamin B12 deficiency in patients undergoing bariatric surgery: preventive strategies and key recommendations." The American Journal of Clinical Nutrition: "How common is vitamin B-12 deficiency?" The American Journal of Gastroenterology: "Vitamin B12 deficiency in untreated celiac disease." Top B12 Injections Who Get Them, How Quickly They Work Related Articles 22 Healthy Foods High in B VitaminsAny deficiency of B vitamins can lead to various health conditions

Several reasons may explain the observation that the mean treatment difference was 12.5% in STEP 1 and 8.7% in SELECT
Prinz, F