Vitamin B12: Do You Get Enough?

Vitamin B-12 deficiency can be difficult to diagnose clinically, as its symptoms are often nonspecific including:

* Fatigue (temporary loss of strength)
* Lassitude (listlessness)
* Malaise (a vague sense of illness)
* Vertigo
* Cognitive impairment

However, you definitely have Vitamin B deficiency if you have the following symptoms:

* macrocytic anemia
* peripheral neuropathy
* subacute combined degeneration of the spinal cord

Standard tests to assess vitamin B-12 concentrations are limited because the severity of vitamin B-12 deficiency is not related to vitamin B-12 concentrations.

It is important to accurately identify Vitamin B-12 deficiency. For example, macrocytic anemia, which is a symptom of vitamin B-12 deficiency, may also be caused by folate deficiency. The anemia may have different neurologic features depending on the cause. Therefore, inappropriately treating the condition with folic acid will correct the hematologic signs of vitamin B-12 deficiency but will not address the neurologic symptoms.

Vitamin B-12 deficiency results in elevated serum concentrations of methylmalonic acid (MMA); therefore elevated concentrations of MMA have been suggested to indicate vitamin B-12 deficiency.

However, there is no consensus on cut-off levels of MMA to use to define vitamin B-12 deficiency among elderly people. Among this group, impaired renal function can be an important confounding factor.

Both vitamin B-12 deficiency and folate deficiency are common among older people.

In one study, MMA of less than 200 pmol/L was used to define individuals as being at high risk of vitamin B-12 deficiency.

However, 15 percent to 30 percent of people with high vitamin B-12 concentrations also had elevated MMA concentrations, which indicates that elevated MMA is not always a reliable indicator.

Instead, the ultimate indicator for vitamin B-12 deficiency may be the reduction in MMA concentrations and improvement in clinical symptoms after being treated with vitamin B-12.

Researchers gave the following recommendation for a more reliable screening of vitamin B-12 deficiency: If vitamin B-12 concentration is less than 150 pmol/L, more detailed investigation is required to find an underlying cause and treatment. If vitamin B-12 concentration is between 150 and 200 pmol/L, then use of MMA may help to identify those who require more detailed investigation and treatment.

For the full text, visit American Journal of Clinical Nutrition

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Vitamin B12 Facts