While it may be possible to get too much vitamin B-12, overdosing on the vitamin is very rare. Becoming deficient in B-12 is a much more common health problem. It is important to carefully monitor how much vitamin B-12 you take to ensure that you do not take too much or too little. If you think your vitamin B-12 level is too high, discuss your concerns with a physician.
Vitamin B-12 is one of eight vitamins in the B vitamin complex. All of the B vitamins are water soluble, meaning that your body does not store them in fatty tissue. Vitamin B-12 helps maintain nerve cell health, assists in DNA production, regulates new red blood cell production and promotes other metabolic functions.
Elevated B-12 Levels
Your doctor may treat pernicious anemia, chronic fatigue and other medical problems with vitamin B-12 supplements. People who take high amounts of B-12 supplements could have elevated vitamin B-12 levels. Although your body typically excretes excess vitamin B-12 in the urine, having too much of the vitamin may cause health problems. A 2001 study in "Cancer Epidemiology, Biomarkers & Prevention" found that high vitamin B-12 levels were associated with higher levels of certain types of esophageal and stomach cancers. Elevated levels of vitamin B-12 have also been linked to prostate cancer. However, these findings do not mean that vitamin B-12 overdose will cause cancer or that people should stop taking the vitamin. More research is needed to determine whether having very high vitamin B-12 levels causes health problems.
B12 in Your Diet
Most of the vitamin B-12 in your body comes from the food you eat. Many animal products contain the vitamin. Eating large amounts of liver, clams, fortified breakfast cereals, trout, salmon or beef can elevate your vitamin B-12 levels. If you have high vitamin B-12 levels, you may decide to decrese your intake of these foods. Because your body does not store extra vitamin B-12, your serum levels of the vitamin will decrease following dietary modification. Getting enough B-12 is especially important for vegans, as most people get the vitamin from animal sources. In addition, older adults are at risk for B-12 deficiency because of a decreased ability to absorb the vitamin.
B-12 in Your Multivitamin
Daily multivitamin supplements often contain 100 percent or more of your recommended daily intake for vitamin B-12. Getting any vitamin B-12 from dietary sources puts you over the recommended daily intake level. Stopping use of a daily multivitamin or B complex supplement will decrease your vitamin B-12 intake. Discuss any changes in supplement use with a physician.
How Much is Too Much?
The Institutes of Medicine have not determined a tolerable upper intake level for vitamin B-12, because there is not enough scientific evidence to determine how much vitamin B-12 you can take without suffering ill effects. In general, vitamin B-12 deficiency is much more common than overdose, so you should be careful to get enough of the vitamin through your diet or supplements. Discuss your diet and supplement use with a physician to determine whether your vitamin B-12 intake is appropriate.