Vitamin B12 allows your body to create red blood cells and keeps your nervous system functioning properly. It is the only water-soluble vitamin the body can store, so most people do not develop low levels. While minor decreases in vitamin B12 may go unnoticed, if your level of vitamin B12 falls too low, you may develop anemia, depression or dementia or experience nerve damage.
Your stomach contains parietal cells, which produce and release a protein called intrinsic factor. When you eat foods that contain vitamin B12, the vitamin combines with intrinsic factor so it can pass through your small intestine and into your bloodstream. If your stomach does not produce enough intrinsic factor, it is impossible for your body to absorb vitamin B12. A reduced ability to produce intrinsic factor can occur after an abnormal autoimmune response that destroys the stomach's parietal cells. Surgical removal of all of part of the stomach also can lead to reduced intrinsic factor. In rare cases, a genetic disposition causes a baby to be born without an ability to produce intrinsic factor.
Your small intestine contains small projections called villi and microvilli. These projections are responsible for increasing the surface area of your small intestine and allowing you to absorb important nutrients from your diet. If they are destroyed or damaged, your ability to absorb vitamin B12 decreases. Over time, chronic digestive diseases such as Crohn’s disease and celiac disease can damage the villi and lead to vitamin B12 malabsorption. Bacterial overgrowth, certain medications and infections also can destroy the villi and reduce your ability to absorb B12. Surgical removal of all or part of the small intestine can decrease your ability to absorb the vitamin and lead to low B12 levels.
Because your body can store vitamin B12 and most Americans meet their daily recommendations regularly, it is rare for low vitamin B12 to develop due to poor diet. Those at highest risk are strict vegetarians and vegans, because the only natural dietary sources of vitamin B12 are foods that come from animals, such as meat and dairy. Older adults are also at an increased risk because the ability to absorb vitamin B12 declines naturally with age.
If you do not produce intrinsic factor or you have a chronic disorder that interferes with your ability absorb vitamin B12, you eventually will develop a B12 deficiency, regardless of the amount of the vitamin you eat. Most people with these conditions require lifelong injections of vitamin B12. Injecting vitamin B12 ensures that it enters the bloodstream directly, bypassing the stomach and the small intestine.
This article reflects the views of the writer and does not necessarily reflect the views of Jillian Michaels or JillianMichaels.com.