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Teens are always looking for creative excuses for late homework, low test scores, and waning attention in class. Any who stumbled onto a copy of the September American Journal of Clinical Nutrition may have uncovered the basis for a particularly novel rationalization: "My parents made me a vegetarian."

Plants do not make vitamin B-12, also known as cobalamin. Diets that eschew all animal products can therefore lead to B-12 deficiencies. Because the vitamin plays a key role in some brain functions, toddlers raised from weaning on strictly plant-based foods can experience delays in the acquisition of certain motor skills. In a few instances, infants in strictly vegetarian families have shown severe anemia, dramatic growth retardation, irritability, and in at least one case, went into a coma.

Now, researchers in the Netherlands find that even when parents begin adding animal-based foods to the diets of their formerly strict-vegetarian kids, neurological impairments may persist into adolescence.

Marieke W.J. Louwman and Wija A. van Staveren of the Wageningen Agricultural University and their colleagues assayed cognitive development in 72 young people, age 9 to 15. These included 48 boys and girls who had been raised initially, at least through age 6, on diets free of all animal products. Indeed, each of the formerly strict-vegetarian children had participated in the Dutch group's study that established early childhood neurologic impairments from cobalamin deficiency.

After learning of that earlier study's findings, parents began supplementing their kids' diets with animal products, usually milk or eggs. In the new work, the researchers compared the cognitive performance of these children to that in 24 kids who had been eating a general, meat-laced diet since infancy.

Subtle, Lingering Deficiencies

Each child completed a 90-minute battery of tests. These included assessments of reasoning, abstract thinking, spatial reasoning, ability to combine vague visual images into a meaningful image, attention span, computation speed, short-term memory, word recall, creativity, hand-eye coordination, and decision making.

The researchers also administered questionnaires that asked what each child had been eating over the past few days, and they assayed each volunteer's blood for both B-12 concentrations and a marker (elevated methylmalonic acid) of early B-12 deficiency.

In general, children who ate both plants and meats consumed about double the recommended daily allowance (RDA) for vitamin B-12. Most of those who had consumed B-12 deficient diets during early childhood continued during adolescence to take in less of the vitamin. In fact, although the median B-12 intake of these kids was close to the RDA, 60 percent showed evidence of B-12 deficiency, and 31 percent had intakes of less than 50 percent of the RDA, the researchers report. Though the youngsters now drank milk, ate eggs, or had switched to a meat-laced diet, their consumption of animal products remained too low in most cases "to restore and maintain adequate cobalamin," the researchers conclude.

The new cognitive tests turned up a link between B-12 status and academic skills.

Children who had eaten normal mixed diets all of their life outperformed those who whose both past and present intake of B-12 was beneath the RDA. In particular, kids deficient in B-12 scored substantially lower on tests measuring spatial ability, short-term memory, and "fluid intelligence", which was described as "the capacity to solve complex problems, abstract thinking ability, and the ability to learn."

These findings "point to discernible, though small, effects of cobalamin deficiency on intellectual functioning," van Staveren's group notes.

The researchers now suspect that because these kids were cobalamin-deprived through age 6, their bodies' stores of the vitamin "may never have reached optimal level, and moderate intakes may not have been sufficient for obtaining normal serum-cobalamin status."

...if it walks, swims, or flies

Louwman and van Staveren say that their findings may point to potential problems in all who avoid animal-based foods," whether because of medical reasons, beliefs, or poverty." The latter group could prove to be a huge share of those living in Asia, sub-Saharan Africa, and some countries in Central and South America.

In the United States, however, those most likely to be at risk are children whose parent choose for them to adhere to macrobiotic diets, which tend to exclude almost all foods except fruits, vegetables, and grains.

The new study indicates that parents of these and other strict vegetarians should be certain that some of their children's foods are fortified.

According to the National Research Council, the B-12 RDA for infants is about 0.3 microgram per day. Recommended intakes for older children scale with their size, based on the formula of 0.05 microgram B-12 per kilogram of body weight, up to an adult intake of 2 micrograms per day.

The typical American diet provides far more than that. Indeed, by eating fish, eggs, dairy products, meats, or shellfish, people can easily take in recommended amounts. Explains Victor Herbert of the Mount Sinai School of Medicine in New York, there's plenty of B-12 in "anything that walks, swims, or flies."

The microwave ate my attention span!

The new Dutch study might even provide crafty nonvegetarians some grist for their excuse mill,if they have been reading SCIENCE NEWS over the past few years. To wit: They might argue that any less-than-stellar academic prowess traces to their family's reliance on microwave cooking and heating.

Japanese research a few years back showed that microwave heating saps B-12 from dairy foods and meats at a higher rate than conventional stove-top and oven heating does. In one case, microwaving removed 30 to 40 percent of the vitamin.

However, alert teachers may be able to counter this particular claim by noting that the large B-12 losses occurred only during what might be considered excessive overcooking or heating, such as boiling milk in the microwave for 6 minutes.