Vitamin B12: from anemia to brain function

B12 absorption decreases with age

Cobalamin, or vitamin B12, is an unusually large molecule for a vitamin.  And we need just a tiny dose every day, just 2.4 micrograms for the average adult.  Contrast that with the 1.3 mg requirement for riboflavin (B2).  That’s 500+ times as much B2, by weight.  But while B12 may only be necessary in tiny doses, it plays a significant role in many metabolic systems, from hemoglobin production to nerve function.

The first step in B12 nutrition is consuming B12, and in our meat-happy cuisine, most people get plenty from food.  It’s found in all animal-based foods, from meat and fish to eggs and dairy products.  It’s important to remember that “milk” made from soy, almonds or other plant materials do not contain any B12, unless it’s added by the manufacturer.  Plant foods do not contain B12.  Vegans, who avoid all animal foods, must get B12 somewhere else, unless they eat fortified soy burgers or fortified fake meat products.  A B12 supplement may be necessary for people who don’t eat those.

The second step in the B12 process is absorption, and that’s dependent on age and genetic factors.  Because the molecule is so large, only about 1% of B12 can passively filter into your system from the digestive tract.  Most B12 is carried into your blood by a special molecule called Intrinsic Factor.  Some people have a genetic variation that prevents intrinsic factor from doing it’s job.  The result is B12 deficiency caused by malabsorption.  Because B12 is key for hemoglobin formation, the deficiency results in anemia.  One symptom of pernicious anemia, as it’s called, is enlarged red blood cells.  The treatment is either injections of B12, to bypass the faulty absorption, or massive doses by supplement.  The thinking is, if only 1% is absorbed passively, then 1% of a massive dose might be sufficient.

Elderly people have a hard time absorbing B12 from food.  Decreased stomach acid, with age or from medications, interferes with release of B12 from food, leading to malabsorption.  Because the form of B12 in supplements doesn’t require acid to be absorbable, supplements are an easy solution to this problem.  It’s interesting that another symptom of B12 deficiency is numbness and tingling in legs and arms, along with memory problems, difficulty walking and disorientation.  Many of these symptoms are common in the elderly.  A recent study of B12 status in people over 65 years old linked poor B12 status with brain shrinkage and poor memory.  The subjects were followed for 4-1/2 years.  B12 markers were measured, and the subjects had MRI brain scans and memory tests.  It’s interesting to note that the researchers did not just measure blood levels of B12.  They measured more sophisticated B12 markers that are not typically measured by when your doctor orders routine blood work.

How do you know you’re deficient?  If you’ve been diagnosed with pernicious anemia, you already know.  If you have anemia and other signs, such as enlarged red blood cells, your doctor will likely test for vitamin B12 to see if that’s an issue.  However, considering the study results above, a simple blood test might not tell the whole story about B12 status.

Thanks to the internet, B12 is linked to pretty much every disease under the sun.  B12 injections are popular with some people, who jump on the bandwagon, because they’re tired or have some other symptoms supposedly caused by B12 deficiency.  The problem with this shot gun approach is that real underlying disease may go untreated.  The people who most need to pay attention to B12 status are the elderly, people with pernicious anemia (about 10% of the population) and vegans, who avoid B12-containing foods.  For the elderly and vegans, supplements may be necessary.  If tests show malabsorption due to age, discuss with your doctor whether injections are the right solution.  In some cases, high dose supplements may be just as effective.

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