Facts about Vitamin B12 absorption
Facts about Vitamin B12 absorption
You may be getting plenty of vitamins and minerals from your diet. But how well you absorb these nutrients is the key to whether you will develop any deficiencies or not.
Vitamin B12 has a complex process of absorption that depends on so many factors, which means your body can’t absorb B12 as easily as other vitamins. And this process can easily go haywire in the presence of certain factors. Before we look at these factors, let’s have a quick look at what this amazing vitamin does in the body and what its deficiency could mean to your health.
Among many things, Vitamin B12 is required for:
- Formation and maturation of red blood cells
- DNA synthesis
- Well-functioning brain and nervous system
- Healthy metabolism
Vitamin B12 deficiency causes anemia, fatigue, constipation, gastrointestinal problems, neurological complications (numbness and tingling in the hands and feet, dementia, memory loss, difficulty in maintaining balance, confusion, brain fog) and soreness of the mouth or tongue. Sometimes, these complications may be irreversible if the deficiency is not diagnosed and treated in a timely manner.
Vitamin B12 absorption
Vitamin B12 is a unique mineral in many ways. Unlike most other vitamins, it can be stored by the body in large amounts and this reserve may last up to 3 to 5 years. This is the reason why you may not immediately notice any tell-tale signs of being deficient.
In addition, you don’t usually get it from vegetables and fruits as the water-soluble vitamin is only present in animal derived foods such as meat (especially beef, pork, liver, and other organ meats), poultry, fish, eggs and milk. You can see why vegetarians are at a higher risk of deficiency, unless they are consuming B12 fortified foods.
Sometimes, the body is not able to absorb the vitamin as efficiently as it should – another major cause of deficiency.
Vitamin B12 is absorbed by the body in various steps. While the entire pathway is a lot more complicated, here is a simplistic view of the how it works.
- Vitamin B12 is bound to proteins in food
- Hydrochloric acid and enzymes in the stomach degrade these proteins and release the vitamin.
- Cells in the stomach lining produce intrinsic factor, a protein that binds to the free B12
- Intrinsic factor and vitamin B12 complex is absorbed in the small intestine. Without intrinsic factor, the vitamin passes right through the intestine without being absorbed and is eventually excreted in stool.
- At some stage, the pancreas also provides enzymes and calcium that help in the absorption
The stomach needs to secrete sufficient hydrochloric acid, enzyme and intrinsic factor, failing which vitamin B12 absorption may be significantly impaired. Any problems with the small intestines, where it is finally absorbed, may also affect metabolism of this vitamin.
Factors that affect vitamin B12 absorption
Age
As you age, the stomach produces less acid, which plays a crucial role in absorption. Older people may also be taking certain medications that further cause reduced production of stomach acid.
If there is no problem with intrinsic factor levels (with ae affected by such occurrences as pernicious anaemia and intestinal surgeries), taking vitamin B12 supplements will reverse the deficiency that often springs up in old age. Vitamin B12, present in fortified foods and dietary supplements, is already in free form. So, the amount of stomach acid your body makes will not affect the absorption from these sources.
Medications
Acid-suppressant drugs
Long term use of drugs such as H2 blockers (for example Pepcid and Zantac) and proton pump inhibitors leads to B12 deficiency. [1] These drugs, often prescribed to treat acid reflux, indigestion, heartburn and stomach ulcers, reduce the amount of acid produced by the stomach, hence malabsorption comes about.
Metformin (Diabetes drug)
Metformin is widely prescribed as a first-line treatment for type 2 diabetes. A study published in the Journal of Clinical Endocrinology & Metabolism found that long term use of metformin increases the risk of vitamin B12 deficiency. [2] The study reported that there was a greater prevalence of anemia in people treated with metformin and neuropathy, a consequence of B12 deficiency, and was higher in those taking metformin with low B12. It is believed that long-term usage of metformin impacts B12 absorption.
Another review published in Diabetes and Metabolism found a link between metformin usage and lower levels of vitamin B12. It concluded that B12 levels should be monitored in patients on metformin as they are at an increased risk of deficiency. [3]
These findings are important considering that doctors don’t usually recommend testing B12 levels in those who have been treated with metformin for years.
Pernicious anaemia
Pernicious anemia is an autoimmune condition in which your immune system attacks and destroys cells that make intrinsic factor. People with this condition can’t absorb enough vitamin B12, even if they are consuming a B12 rich diet or B12 supplements in normal doses. In this case, your doctor may prescribe muscular injections that bypass the gastrointestinal route.
Weight loss surgery and intestinal disorders
Gastric bypass surgery (for weight loss) or other surgical procedures that remove parts of the stomach, reduces the cells that make gastric acid and intrinsic factor. This interferes with the body’s ability to absorb vitamin B12. Surgeries that involve removing small intestines also affect this ability.
Diseases that cause inflammation in the digestive tract, such as Crohn’s disease and celiac disease also lead to malabsorption of nutrients, including B12, as does pancreatic disorders.
Heavy drinking
Consuming more than a few drinks every day can irritate the lining of the stomach, which affects the acid production and makes absorption difficult. Heavy use of alcohol may also cause liver damage. Since most of the body’s reserve of B12 is stored in the liver, this may impact how effectively the liver stores the vitamin.
Overgrowth of bacteria
Overuse of antibiotics and conditions such as diabetes, scleroderma and intestinal scarring from surgeries and inflammatory bowel diseases cause excessive growth of bacteria in intestine. These bacteria use the available B12 for their own growth, leaving less amounts to be absorbed by the small intestine. [4]
References:
- Lam JR, Schneider JL, Zhao W, Corley DA. Proton Pump Inhibitor and Histamine 2 Receptor Antagonist Use and Vitamin B12 Deficiency. JAMA. 2013
- VR Aroda et al. Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab. 2016
- Chapman LE et al. Association between metformin and vitamin B12 deficiency in patients with type 2 diabetes: A systematic review and meta-analysis. Diabetes Metab. 2016
- Vitamin B12 Deficiency. Harvard Health Publications. 2013.
