For IDEAL WEIGHT, vitamin B12 helps maintain a lively metabolic rate, because it is essential to convert fats and proteins into energy and to break down carbohydrates. It is also necessary for nervous system function. In addition, vitamin B12 is needed for red blood cell formation and maturation, and it restores critical DNA synthesis and activity in every cell. Most importantly for ideal weight, vitamin B12 functions as a cofactor in an essential biochemical reaction in fat and protein metabolism. For all these reasons, if vitamin B12 levels are low, the body slows its metabolism to conserve B12, making weight loss harder.

A deficiency in vitamin B12 can sabotage body processes responsible for weight management. Symptoms of deficiency include exhaustion, weakness, dizziness, and shortness of breath. Lower energy leaves people reluctant to exercise and with reduced endurance. Since exercise relies upon the circulatory and respiratory systems which can be hampered by low B12 levels, it can become a vicious cycle. Vitamin B12 deficiency can also lead to long-term weight control problems. When the body’s natural balance is disrupted, and lacking essential nutrients, it typically responds by slowing down the metabolic rate, conserving fat stores, and burning fewer calories throughout the day. Evidence from the Framingham Offspring Study suggests that the prevalence of vitamin B12 deficiency might be greater than previously assumed. This study found that the percentage of participants in three age groups (age 26-49 years, 50-64 years, and 65 years and older) with deficient blood levels of vitamin B12 was similar, ranging between 39% with low levels and 17% with extremely low levels.1   

Vitamin B12, or cobalamin, is a water-soluble vitamin that is needed in the metabolism of every cell of the human body. It is the largest and most structurally complicated of the B vitamins. Vitamin B12 is required for proper red blood cell formation, neurological function, and DNA synthesis. Neither fungi, plants, nor animals can make vitamin B12 themselves. It is only abundant in red meats, organ meats like liver, and eggs, and so many people have very limited amounts in their diets.

Because vitamin B12 does not occur in many foods and it has a complicated route of absorption, deficiency is very common. In our clinic we check blood B12 levels routinely, and we find that maybe 30 to 50% of people have insufficient levels. Additionally, modern diets are typically saturated with highly processed foods, which can aggravate B12 deficiencies. Vegan and vegetarians receive little or no vitamin B12 in their diets.

The absorption of vitamin B12 is fraught with hurdles: In the stomach, vitamin B12 must bind with a protein called Intrinsic Factor to absorb. It also needs sufficient acid to release it from protein foods. Then it must travel many feet through the small intestine to the far end, the terminal ileum, a very specialized small area where it can pass into the blood stream. Any stomach disorders, low acid output or acid-blocking drugs, or conditions like pernicious anemia where Intrinsic Factor is lacking, can prevent B12 absorption, as can intestinal inflammation such as Crohn’s disease if a damaged terminal ileum cannot take up vitamin B12.

Since poor absorption can be a problem with vitamin B12, we always give patients a formula that dissolves under the tongue to absorb into veins in the mouth. This circumvents the stomach and intestine so that the B12 can directly enter the blood stream. Nowadays, sublingual vitamin B12 formulas are so efficiently absorbed and effective that patients almost never need injections. Studies as early as 1998 validate correct oral treatment to be equally effective as injections, with a conclusion that in cobalamin deficiency, 2,000mcg of cyanocobalamin administered orally on a daily basis is as effective and may be superior for raising blood B12 levels as 1,000mcg administered intramuscularly on a monthly basis.6

In our clinic, many of our patients have excellent results with a sublingual vitamin B12 that dissolves gradually in about 15 minutes under the tongue. We measure their blood B12 levels beforehand, and often see a big increase within 6 to 8 weeks. We recommend a lozenge formulation with only natural flavorings. It is best taken in the morning or afternoon as it may cause a quick energy boost. Ideally, we like to use a vitamin B12 that is combined and balanced with an ample amount of folic acid, which should be included in a patient’s overall supplement intake to make sure that a folic acid deficiency is not masked.

Recommendation: Vitamin B-12 (as cyanocobalamin) 2,500 to 5,000mcg, dissolved slowly under the tongue, in the morning or early afternoon, once daily, or as directed by your healthcare provider. It is unrelated to food and does not matter if a meal has been eaten, as B12 circumvents the stomach to absorb into veins around the tongue. Folic acid 400 to 800mcg daily should also be ingested either with B12 or in a multivitamin or B-vitamin formula.


  1. Tucker KL, Rich S, Rosenberg I, Jacques P, Dallal G, Wilson WF, et al. Plasma vitamin B12 concentrations relate to intake source in the Framingham Offspring Study. Am J Clin Nutr 2000;71:514-22.
  2. Carmel R, Sarrai M. Diagnosis and management of clinical and subclinical cobalamin deficiency: advances and controversies. Curr Hematol Rep 2006;5:23-33.
  3. Read, A. E., and Richard Asher. “Weight loss and pernicious anaemia.” Lancet 270 (1956): 882-884.
  4. Weight, Lindsay M., et al. “Vitamin and mineral status of trained athletes including the effects of supplementation.” The American journal of clinical nutrition 47.2 (1988): 186-191.
  5. Karatela, R. A., and G. S. Sainani. “Plasma homocysteine in obese, overweight and normal weight hypertensives and normotensives.” Indian heart journal 61.2 (2009): 156-159.
  6. Kuzminski AM, Del Giacco EJ, et al. Effective treatment of cobalamin deficiency with oral cobalamin. Blood 1998;92:1191-1198.