Megaloblastic anemia (due to vitamin B12 deficiency)
Low levels of vitamin B12 are a cause of megaloblastic anemia, in which red blood cells are larger than normal. Other possible causes include folate deficiency or various metabolic disorders. Anemia should be diagnosed by a physician to address the underlying cause.
Vitamin B12 deficiency
Studies have shown that a deficiency of vitamin B12 can lead to abnormal mental symptoms. These symptoms may include ataxia (shaky movements and unsteady gait), muscle weakness, spasticity (stiff or rigid muscles), incontinence (lack of bladder and/or bowel control), hypotension (low blood pressure), vision problems, dementia, psychoses (abnormal condition of the mind), and mood disturbances. Giving vitamin B12 by mouth, by injection, or by nasal inhalation is effective for preventing and treating dietary vitamin B12 deficiency.
Some people diagnosed with Alzheimer's disease have been found to have abnormally low vitamin B12 levels in their blood. The effects of vitamin B12 supplementation on the prevention or progression of Alzheimer's disease remain unclear. More studies are needed before a conclusion can be made.
Angioplasty (opening narrowed/blocked arteries)
Some evidence suggests that giving prescription-strength folic acid and vitamins B12 and B6 for six months following coronary angioplasty reduced the risk of overall adverse cardiac events; however, other studies have found this combination to increase restenosis (reoccurrence of narrowing of a blood vessel). Further research is needed before a conclusion can be made.
Researchers have reported that women with breast cancer tend to have lower vitamin B12 levels in their blood serum than do women without breast cancer. However, one study found that giving a combination of folic acid, vitamin B6, and vitamin B12 failed to decrease the risk of breast cancer. Further research is needed before conclusions can be made.
Vitamin B12 and vitamin B12 injections combined with hydrocortisone were studied to treat recurrent canker sores; although treatment with sublingual vitamin B12 may have some benefit, further research is needed before a conclusion can be made.
High homocysteine levels in the blood have been suggested as being a risk factor for cardiovascular disease, blood clotting abnormalities, atherosclerosis (hardening of arteries), heart attack, and stroke (due to a blood clot). Taking vitamin B12 supplements in combination with other B vitamins (mainly folic acid) has been shown to be effective for lowering homocysteine levels. It is unclear whether lowering homocysteine levels has an effect on cardiovascular disease risk and death. More evidence is needed.
Some evidence suggests that vitamin B12 supplementation may have a role in preventing cervical cancer. Further research is warranted in this area.
Claudication (leg pain from clogged arteries)
Human research evaluated the effects of vitamin B12 and results demonstrated that although walking distance was improved, sufficient high quality evidence was lacking. Further research is needed before a conclusion can be made.
A combination of folic acid, vitamin B12, and vitamin B6 lacked any difference in symptoms of depression in older men as compared to placebo. Well-designed clinical trials are needed to confirm any potential benefit.
Diabetic neuropathy (nerve damage)
Some evidence suggests that supplementation with vitamin B12 may be helpful in people with diabetic neuropathy. More research is needed in this area.
In order to detect the presence of vitamin B12, lab tests to measure plasma and serum vitamin B12 may be used; however, many investigators believe testing is unreliable. Research has reported that diagnosis of vitamin deficiencies cannot be made by evaluating vitamin B12 levels alone.
Research has reported that vitamin B12 lacked any benefit over acupuncture in treatment of facial spasm. Further research is needed before a conclusion can be made.
There is some evidence that vitamin B12 injections given twice weekly may improve the general well-being and happiness of people complaining of tiredness or fatigue. Further studies are needed before a conclusion can be made.
Some evidence suggests that a combination of vitamins including vitamin B12 may help prevent fractures. More research is needed.
Some evidence suggests that vitamin B12 in combination with fish oil may be better than fish oil alone when used daily to reduce cholesterol and triglyceride levels. More studies are needed before a conclusion can be made.
Vitamin B12 injections may be effective for treating a hereditary form of vitamin B12 malabsorption (Imerslund-Grasbeck disease). Further research is needed to confirm these results.
Joint pain (elbow)
Preliminary research suggests that vitamin B12 may be effective for elbow pain, but evidence is lacking. Further research is needed.
Increased homocysteine levels have been associated with lower mental testing scores. However, there was a lack of association between low vitamin B12 blood levels and mental decline, Alzheimer's disease, or dementia. More research is needed before a conclusion can be made.
Hydroxocobalamin (a chemical form of vitamin B12) has been approved by the United States Food and Drug Administration (FDA) since 2006 as a potential antidote for treatment in people with suspected smoke inhalation cyanide toxicity, and although research is lacking on the use of hydroxocobalamin in pregnant women, it did gain FDA approval in pregnant women in 2010. In addition, according to the Australian Resuscitation Council, serious adverse effects with hydroxocobalamin were lacking, and many people with fatal cyanide poisoning had survived.
Clinical reports show that shaky-leg syndrome may be due to vitamin B12 deficiency. Further research is needed to confirm these results.
Sickle cell disease
Early study suggests that a daily combination including folic acid, vitamin B12, and vitamin B6 may reduce endothelial (cells lining vascular walls) damage in people with sickle cell disease. Further research is needed to confirm these results.
Sleep disorders (circadian rhythm)
Taking vitamin B12 by mouth lacked any effectiveness for treating delayed sleep phase syndrome. Giving vitamin B12 with bright light therapy may be helpful for adolescents with circadian rhythm sleep disorders. More research is needed in this area.
One study found an increase in lung cancer in people with heart disease in Norway whom were taking vitamin B12 and folic acid. More research is needed to better understand this relationship.
In people with a history of stroke, neither high-dose nor low-dose vitamin B12 combinations containing vitamin B6, vitamin B12, and folic acid seem to affect risk of recurring stroke.