Are you getting enough of this vitamin?

If you're a vegetarian or over age 60, you need to be concerned about getting enough vitamin B12.

Lately, there's been increased concern about going overboard with vitamins. Researchers have found that a high intake of vitamin A in its retinol form is associated with a high rate of fractures. Other studies have cast a cloud of suspicion over vitamin E supplements.

Vitamin B12, though, is different: It is easier than once thought to get too little. Studies have found that 20% of Americans ages 65 and over have low levels of the vitamin in their blood. Sometimes the only symptoms are subtle cognitive and neurological changes. More serious shortages can result in dementia or anemia, because B12 is essential for the production of red blood cells in the bone marrow. Breast-fed infants of mothers with a B12 deficiency are at risk for severe developmental abnormalities and irreversible neurological damage. Some experts say that it's the most common nutritional deficiency in the developing world and possibly in the United States as well.

In this country (and other prosperous places) the problem isn't hard to solve. A multivitamin or a vitamin-fortified breakfast cereal (B12 is usually included) will do the trick. In fact, the crystalline form of the vitamin contained in pills and breakfast cereals is more readily absorbed than the "natural" form found in food.

Solving nutrition problems in poor countries is never easy, but inexpensive programs that involve adding milk or meat to school meals have been effective in correcting B12 deficiencies.

The carnivore's vitamin

When we think about natural sources of vitamins, we usually think of fruit and vegetables. But plants neither use nor contain vitamin B12, so the only dietary sources are animal-derived: meat, fish, shellfish, poultry, eggs, milk, and milk products. Beef liver and several varieties of fish contain high amounts, dairy products and eggs not so much. Vegetarians can eat tempeh, which is made from fermented soybeans (the bacteria produce B12).

Four ways deficiencies develop

In normal digestion, stomach juices pry B12 loose from animal protein. But the small intestine can't absorb the vitamin in this liberated, solo state. To be absorbed, it must be combined with a protein called intrinsic factor that is produced by cells in the lining of the stomach.

It may take quite a while for a deficiency to develop. A healthy person's liver can store up to a five-year supply of B12. And the small intestine does a marvelous job of B12 recycling, reabsorbing it from bile made by the liver. Of course, a deficiency will develop sooner if reserves are low to begin with.

Diets without food derived from animals. In poor countries, people often have to eat this way. In richer ones, many people choose animal-free diets. Vegans, the strict vegetarians who avoid all animal products, are most at risk for developing a full-fledged B12 deficiency. But even lacto-ovo vegetarians, who eat eggs and dairy products, may have low levels. Studies have found that the average lacto-ovo vegetarian consumes less than 1 microgram (mcg) daily, which is less than half the adult Recommended Dietary Allowance (RDA) of 2.4 mcg.

Lack of stomach acid. Up to 30% of people ages 50 and over suffer from atrophic gastritis, a thinning of the stomach lining. This condition reduces the acid secretions that free B12 from animal protein, so much less is absorbed by the small intestine.

Lack of stomach juices may also allow the overgrowth of bacteria in the small intestine. The bacteria grab B12 for their own purposes, leaving less for the intestine to absorb.

Theoretically, drugs like lansoprazole (Prevacid) and omeprazole (Prilosec) could cause B12 problems because they suppress gastric secretions. But so far, B12 deficits have not been linked to long-term use of these or other drugs that reduce stomach acid.

Lack of intrinsic factor. Some people's stomachs don't make enough intrinsic factor, so they can't absorb enough B12. The cause is an autoimmune disorder: The body's immune system gets confused and produces antibodies, which, instead of chasing down germs as they should, pounce on the stomach cells that produce intrinsic factor. The result can be anemia. This consequence was recognized long before the cause, so the condition is called pernicious anemia (pernicious because, until it was identified, it was inevitably fatal). It runs in families, suggesting a genetic component, and usually develops after age 40. Less than 1% of the population is affected.

Gastrointestinal disorders and surgeries. Crohn's disease might cause a B12 shortage because it interferes with the functioning of the small intestine. Some people develop a B12 shortage after a surgical procedure that shrinks the stomach, such as gastric bypass, because a smaller stomach means far fewer of the cells secreting stomach acid and intrinsic factor.

Solutions

Vegetarians and older people with atrophic gastritis can get all the B12 they need from a multivitamin pill, fortified breakfast cereal, or both. Most multivitamins contain 6 mcg, which is 100% of the Daily Value set by the FDA. (The RDA of 2.4 mcg was set by the Institute of Medicine. The difference between the two amounts is probably not important.) Fortified breakfast cereals have varying amounts of B12.

People with pernicious anemia have a more difficult problem. Because they're short on intrinsic factor, they don't benefit from the extra B12 in vitamin pills and fortified cereal. At least initially, most need B12 injections. After that, some do fine with pills alone, but others need additional injections every few months.

Some researchers think high-dose pills (2,000 mcg or more) could be just as effective as injections for pernicious anemia. There's some evidence that about 1% of the B12 in pills is absorbed by simple diffusion, regardless of intrinsic factor or the state of the intestine. Studies suggest that even if they don't have pernicious anemia, older people with fairly mild deficits may need to take similarly large doses of B12 to bring their levels up to normal. More research is needed, though. Fortunately, even very large doses of the vitamin don't seem to pose any danger.

People with Crohn's disease and other malabsorption problems may also need B12 injections depending on the severity of their condition. Gastric bypass patients may need them, too.

Should you be tested?

Those at risk for B12 deficits include older people and strict vegetarians. Research also suggests that long-term use of metformin, the diabetes drug, may lower B12 levels. Although a severe deficiency is fairly unlikely, lesser shortfalls may affect balance, memory, or perhaps mood. If you have these problems and you're in an at-risk category, ask your doctor about ordering a B12 test. It's a common, inexpensive blood test that could make a big difference in your life.