Imagine having a disease that will very likely kill you—unless you can somehow choke down 2/3 pound of raw liver a day. Awful? Yes. But that was once the cure offered to people with pernicious. The researchers who discovered this cure won the Nobel Prize for medicine in 1934. It wasn’t until 1948 that researchers isolated from raw liver the small red crystals of the nutrient that we now call vitamin B12.
Unless you’re a vegan (strict vegetarian), pernicious is not often due to a lack of this essential vitamin. It’s actually a problem with absorption. B12 differs from other vitamins in that before it can be absorbed into the cells lining the intestines, it has to hook up with a protein called intrinsic factor that is secreted as part of the stomach’s digestive juices.
Some people, especially when they’re older and on low-protein diets, don’t make enough intrinsic factor to absorb all the B12 they need. Since intrinsic factor is provided by the body, not by food, when the body doesn’t make enough, we can be at risk for B12-related health risks.
Only about 1 percent of people develop the classic symptoms of B12 deficiency— and nerve damage. About 30 percent of older people show signs of deficiency when their blood is tested, says Robert Allen, M.D., professor of medicine and biochemistry and director of hematology at the University of Colorado Health Sciences Center in Denver.
Even a low-level deficiency can have negative health effects. People may have depression, forgetfulness, trouble walking, and even incontinence. Sometimes, though, these are problems of old age rather than an outcome of vitamin deficiency. That’s why proper testing is so important.
B12 Basics
This vitamin is essential to every cell in your body. It must be on hand for DNA synthesis, the process by which your body makes the genetic material that comprises the cell nucleus. Vitamin B12 is far more than a cheerleader in this process. It rolls up its sleeves and goes to work, helping to make the nucleic acids that are strung together like pearls to form DNA, the genetic e-mail system. It also helps make RNA, the copy of DNA that’s sent along to each cell.
When cells are rapidly dividing, as they do during growth and development, more B12 is needed for this process, according to John Pinto, Ph.D., associate professor of biochemistry at Weill Medical College of Cornell University and director of the nutrition research laboratory at Memorial Sloan-Kettering Cancer Center, both in New York City. Extra B12 is also necessary in areas where cells normally have rapid turnover, such as the intestines and blood, he says.
When B12 is in short supply, DNA and RNA synthesis slows, and cells can no longer divide and multiply. This can show up in several ways. In the blood, it can mean —a shortage of red blood cells—since the cells in the bone marrow that make red blood cells normally crank them out at the rate of at least 200 million a minute. In the intestines, it can mean absorption problems that create a domino effect, accelerating nutrient deficiencies as cells are deprived of the supplies that are delivered like groceries by the red blood cells.
SUPPLEMENT SNAPSHOT
| Vitamin B12 Also known as: Cobalamin; cyanocobalamin. May help: Pernicious and nerve problems related to B12 deficiency; sometimes used for shingles, multiple sclerosis, canker sores, diabetes, depression, and binge-eating disorder and to help delay progression of HIV to AIDS. With vitamins B6 and folic acid, can lower blood levels of homocysteine to reduce risk of heart attack and prevent intermittent claudication, phlebitis, Alzheimer’s disease, angina, and high blood pressure. Daily Value: 6 micrograms. Special instructions: People with B12 deficiencies might not be able to rely on oral supplements and should see a doctor, who may recommend B12 injections as well as other supplementation. Who’s at risk for deficiency: People age 60 or older who have a condition that causes low stomach acid, people with problems related to intrinsic factor, people with Crohn’s disease, strict vegetarians, and breastfed babies of strict vegetarians. Good food sources: Cooked oysters and clams and all meats. Cautions and possible side effects: Generally regarded as safe. |
In some places in the body, such as the cervix and intestines, a shortage of vitamin B12 can begin to interfere with cell growth; the resulting cell abnormalities can lead to cancer. Your ability to fight infection may slow down because your body can’t crank out enough infection-fighting white blood cells. In fact, one study showed that people with HIV, the virus that causes AIDS, were able to hold off full-blown AIDS longer if they had high levels of B12. "The bottom line is, how fast can your system adapt to an adverse situation, such as infection, by making more DNA?" Dr. Pinto says. "When B12 is in short supply, your body slows down and can’t defend itself as well."
Friend of Folic
Vitamin B12 works hand in hand with folic acid, which also helps to make DNA. One form of folic acid circulates throughout the body. When B12 removes a piece of the molecule from this circulating form, the folic acid becomes available for other reactions. As it goes about its business, B12 uses the stolen piece of molecule for some of its own important functions.
Since B12 and folic acid are so closely linked, a deficiency of one can leave the other in cold storage. You may be getting plenty of folate (the food form of folic acid) in your diet, for instance, but if you’re coming up short on B12, the folate stays inside cells, trapped in its inactive form.
The Amino Acid Shuffle
Vitamin B12 and folic acid are also necessary for amino acid synthesis, meaning that they need to be there when your body sends the wrecking ball up against the proteins in food and then reassembles those proteins to create new structures.
This demolition and reconstruction work is going on all the time. If your body wants to take those scrambled eggs you had this morning and turn them into useful energy and hearty body cells, B12 and folic acid have to be on hand to do their part. They help to ensure that the protein parts—amino acids—are in the proper amounts to make new proteins.
| Should You Have a B12 Test? Doctors are usually pretty good about checking blood levels of B12 when a patient shows signs of or severe nerve damage, but sometimes the early signs of deficiency can escape a doctor’s notice. Among the less noticeable symptoms of vitamin B12 deficiency are numbness and tingling in the feet or hands, loss of balance, and memory loss or disorientation. “Doctors should be testing people when they have these symptoms,” says Robert Allen, M.D., professor of medicine and biochemistry and director of hematology at the University of Colorado Health Sciences Center in Denver. “And if B12 is in the low-normal range, they should do a follow-up test that measures two additional things, methylmalonic acid and homocysteine. This test is very useful because it helps us accurately diagnose a deficiency and distinguish between a deficiency of B12 and one of folic acid. “Too many doctors still follow the old textbook rule from 10 years ago,” Dr. Allen says. “They don’t give their patients B12 injections unless their blood levels are below 100, and that’s clearly a mistake. It is now clear that many people who have levels in the 200- to 300-range require treatment or further evaluation.” |
As the redevelopment authority inside your body, B12 can make trouble for your heart if it goes on strike. Along with folic acid and B6, it is needed to break down an amino acid by-product called homocysteine. When you don’t have enough, blood levels of homocysteine rise, "and high levels of homocysteine seem to increase your risk for heart disease and stroke even more than high cholesterol," Dr. Pinto says.
Homocysteine damages the cells lining the blood vessels, creating rough spots that attract cholesterol deposits and issue invitations for blood to start clotting. Exactly how much of the three B vitamins you need to prevent this problem isn’t known. In one study where people received daily doses of 400 micrograms of B12, 1 milligram of folic acid, and 10 milligrams of B6, homocysteine levels dropped significantly.
So far, researchers have found that high levels of homocysteine are associated with heart disease and that B vitamins can help lower homocysteine levels. They are trying to complete the circle by showing that lowering homocysteine levels with B vitamins can also lower heart disease risk, says Dr. Allen.
Nerves of Steel
Vitamin B12 also maintains the fatty sheath, called myelin, that surrounds and protects nerve fibers and promotes their normal growth, Dr. Pinto says. Like insulation around copper wires, this sheath allows your radiating network of nerves to send their electrical messages without short-circuiting. When B12 is missing, the myelin sheath breaks down, which eventually leads to nerve damage.
Researchers used to think that since B12 was needed to put together the fatty acids that make up the myelin sheath, a fatty acid problem caused nerve damage. "Now it looks more like this, too, is a problem with high homocysteine levels," Dr. Pinto says. "Homocysteine seems to be directly toxic to nerve cells."
This may partly explain the symptoms of B12 deficiency—numbness, tingling feet or hands, trouble walking, memory loss, and personality and mood changes. It doesn’t explain everything, though, since only about one-third of B12-deficient people develop these symptoms, Dr. Allen says. "My feeling is that these symptoms are caused by a combination of deficiency and some environmental or genetic factor."
