Vitamin B12 (cobalamin)

In 1849, Dr. Thomas Addi­son described the first doc­u­ment­ed cas­es of what is now called “per­ni­cious ane­mia.” The patients were pale and weak and got sick­er and sick­er until they inevitably died. Peo­ple with per­ni­cious ane­mia don’t have enough red blood cells, and many of the ones they do have are abnor­mal­ly large. Unlike oth­er forms of ane­mia, the con­di­tion didn’t respond to any avail­able treat­ment, and it seemed to affect the ner­vous sys­tem as well as the blood. Even­tu­al­ly, doc­tors real­ized that per­ni­cious ane­mia was a major pub­lic health prob­lem, affect­ing about 1% to 2% of the adults over age 50 in the Unit­ed States. It occurred main­ly in peo­ple of Euro­pean ances­try.

By 1880, it was clear that per­ni­cious ane­mia result­ed from dam­age to the lin­ing of the stom­ach. The stom­ach was fail­ing to secrete some­thing (lat­er called “intrin­sic fac­tor”) that the body need­ed in order to get a par­tic­u­lar nutri­ent from food. The impor­tance of a healthy stom­ach was lat­er proved through a clever, though dis­gust­ing exper­i­ment. Healthy peo­ple were fed a big serv­ing of ordi­nary beef, which was allowed to digest for a while in their stom­ach. Then the par­tial­ly digest­ed beef was pumped from their stom­ach and fed to some­one with per­ni­cious ane­mia, who was then able to make nor­mal new red blood cells!

In the 1920s, researchers at Har­vard Med­ical School fig­ured out that they could keep peo­ple with per­ni­cious ane­mia alive if they fed them huge amounts of liv­er. Liv­er con­tains an enor­mous dose of what­ev­er it is that cures per­ni­cious ane­mia, enough to com­pen­sate for poor absorp­tion. Researchers then test­ed var­i­ous kinds of liv­er extracts, to see if they could iso­late and iden­ti­fy that nutri­ent. They found a water-sol­u­ble organ­ic com­pound that con­tains the metal­lic ele­ment cobalt and named it vit­a­min B₁₂.Three of the researchers who con­tributed to solv­ing this puz­zle won the 1934 Nobel Prize in Med­i­cine or Phys­i­ol­o­gy.

Although per­ni­cious ane­mia is due to a defi­cien­cy of vit­a­min B₁₂, most of the peo­ple who were get­ting the dis­ease were eat­ing food that con­tained more than enough vit­a­min B₁₂. They sim­ply weren’t absorb­ing the vit­a­min. The vit­a­min B₁₂ that occurs nat­u­ral­ly in ani­mal-based food tends to be bound to pro­tein. The acid in the stom­ach helps to break the vit­a­min B₁₂ free from those pro­teins. Then the vit­a­min B₁₂ binds to anoth­er pro­tein pro­duced by the stom­ach itself. This pro­tein is called intrin­sic fac­tor. When vit­a­min B₁₂ is bound to intrin­sic fac­tor, it is very eas­i­ly absorbed from the intes­tine. If the stom­ach doesn’t pro­duce intrin­sic fac­tor, only about 1% of a very large dose of vit­a­min B₁₂ would get absorbed into the blood­stream.

In oth­er words, peo­ple with a nor­mal diges­tive sys­tem can effi­cient­ly absorb vit­a­min B₁₂ from their food or from a sup­ple­ment they take by mouth. Peo­ple whose stom­ach doesn’t make intrin­sic fac­tor can’t absorb vit­a­min B₁₂ effi­cient­ly from their food or from sup­ple­ments. They can meet their needs for vit­a­min B₁₂ either by get­ting vit­a­min B₁₂ shots (thus bypass­ing the need for intrin­sic fac­tor) or by tak­ing such huge dos­es of vit­a­min B₁₂ by mouth that they end up absorb­ing enough to meet their needs.

The­o­ret­i­cal­ly, you could also get a vit­a­min B₁₂ defi­cien­cy by eat­ing a diet that doesn’t con­tain enough vit­a­min B₁₂. Dietary defi­cien­cy of vit­a­min B₁₂ wouldn’t be a prob­lem for car­ni­vores or omni­vores, because ani­mal-based foods con­tain vit­a­min B₁₂. Even though plant foods don’t con­tain vit­a­min B₁₂, most plant-eat­ing species don’t have a prob­lem with vit­a­min B₁₂ defi­cien­cy. That’s because they can absorb the vit­a­min B₁₂ that is made by bac­te­ria in their diges­tive tract.
Cat­tle and sheep are par­tic­u­lar­ly good at get­ting vit­a­min B₁₂ from their gut bac­te­ria. That’s because plen­ty of vit­a­min B₁₂ is being pro­duced in the stom­ach and is then absorbed in the small intes­tine. So “foregut fer­menters” like cat­tle and sheep nev­er have a prob­lem with vit­a­min B₁₂ defi­cien­cy as long as there’s some source of cobalt in their food.

The prob­lem gets a bit tricky for “hindgut fer­menters” like rab­bits and goril­las and human beings. In a hindgut fer­menter, the bac­te­r­i­al action that pro­duces vit­a­min B₁₂ is pro­duced in the large intes­tine, too late for the vit­a­min to be absorbed in the small intes­tine. Rab­bits solve this prob­lem by eat­ing some of their own drop­pings. Goril­las might do the same thing, but they prob­a­bly get enough vit­a­min B₁₂ from the ter­mites and oth­er creepy crawlies in their diet. Although plant foods don’t con­tain any vit­a­min B₁₂,  peo­ple who don’t eat ani­mal prod­ucts can eas­i­ly get vit­a­min B₁₂ from a nice clean sup­ple­ment.

Most cas­es of vit­a­min B₁₂ defi­cien­cy in human beings result from a dis­ease of the stom­ach. Dietary defi­cien­cy of vit­a­min B₁₂ is extreme­ly rare, even among alco­holics, veg­e­tar­i­ans, and mal­nour­ished peo­ple and peo­ple with liv­er or kid­ney dis­ease.  That’s prob­a­bly because the liv­er can store over a 3-year sup­ply of the vit­a­min. There have been a few reports of vit­a­min B₁₂ defi­cien­cy in peo­ple who eat noth­ing but plant-based foods or in babies breast-fed by women with a vit­a­min B₁₂ defi­cien­cy.

Peo­ple who eat no ani­mal prod­ucts what­so­ev­er are strong­ly encour­aged to take a vit­a­min B₁₂ sup­ple­ment. It’s pos­si­ble to get “per­ni­cious ane­mia” with­out hav­ing ane­mia. In oth­er words, if you have plen­ty of folic acid in your sys­tem, you can end up with the nerve dam­age from vit­a­min B₁₂ defi­cien­cy with­out the low red blood cell count and abnor­mal red blood cells that would help your doc­tor fig­ure out what’s wrong. This could allow the nerve dam­age to progress unde­tect­ed. This was one of the draw­backs to using folic acid sup­ple­ments instead of eat­ing foods that con­tain nat­ur­al folate.

Start­ing in the late 1990s, the U.S. Food and Drug Admin­is­tra­tion start­ed requir­ing refined cere­al prod­ucts, such as white bread and pas­ta, to be for­ti­fied with folic acid. The pur­pose of this for­ti­fi­ca­tion was to pre­vent birth defects by mak­ing sure that women had enough folate in their sys­tem when they became preg­nant. This pol­i­cy has reduced the num­ber of babies born with severe birth defects, such as paral­y­sis from an open spine. Unfor­tu­nate­ly, the folic acid for­ti­fi­ca­tion could end up caus­ing cas­es of per­ni­cious ane­mia in elder­ly peo­ple to be over­looked until severe nerve dam­age occurs.Pho­to by icethim