Adolescents who were fed a strict macrobiotic diet during infancy and early childhood show signs of impaired cognitive function, according to a study by Louwman et al. published in The American Journal of Clinical Nutrition. The macrobiotic diet, usually adhered to by families due to religious beliefs or purported health benefits, is similar to a vegan diet in that animal products are avoided and vitamin B-12 content is very low. Adolescents in the study who had consumed the diet until an average age of 6 years and had tested B12-deficient the year before the study scored significantly lower than other groups of adolescents on tests measuring intelligence, spatial ability and short-term memory.
The authors compared three groups of adolescents who were otherwise matched for age and socioeconomic status. Two groups had previously been fed a macrobiotic diet as babies and young children, though their diets had subsequently been altered at an average age of 6 to lactovegetarian or omnivorous. The year before the current study one of the groups tested vitamin B-12 deficient (31 adolescents), while the other group tested in the normal range of vitamin B-12 (17 adolescents). A third control group of 24 adolescents had been raised since birth on an omnivorous diet including meat and dairy products. A year after the measurement of B12 status, all three groups were administered a broad spectrum of psychological tests using standard methods to measure cognitive abilities and some aspects of psychomotor functioning. After adjustment for age, a significant association appeared between the adolescents' serum B-12 concentrations and their performance on the fluid intelligence portion of the test. The association was most pronounced in the group of adolescents who, the year before, had been B12 deficient. According to the authors, "Fluid intelligence is important because it involves reasoning, the capacity to solve complex problems, abstract thinking ability, and the ability to learn. Any defect in this area may have far-reaching consequences for individual functioning." A significant association was also found between serum B-12 concentrations and performance on the spatial ability and short-term memory portions of the test.
Vitamin B12 is found only in animal products and hence is entirely absent from vegan diets and nearly so from macrobiotic diets, which may contain small amounts of fish. Severe B12 deficiency in infants and children has previously been shown to produce delayed psychomotor development and growth retardation. The earliest signs of vitamin B12 deficiency in infants include apathy and lethargy which is often accompanied by increasing irritability. B12 deficient adults and children may show neurological effects such as lack of coordination, loss of skin sensation, diminished reflexes, dementia, loss of memory, psychosis and mood disturbances. These macrobiotic subjects were somewhat unique because the parents of these Dutch adolescents were generally well-educated and of higher socioeconomic status. Of the macrobiotic adolescents who had tested B12 deficient the year before the study, 77% still had low B12 concentrations at the time of the study. This was most likely due to the fact that their body stores may never have reached an optimal level as infants and young children, and even after changing to a lactovegetarian or lactoovovegetarian diet, their moderate intakes of animal products were not sufficient to bring them to normal B12 status.
The authors stress that the findings of their study point to an association, but not a proven causal relationship, between B-12 status and cognitive functioning. Nevertheless, the implications of the study are significant for any population that may be avoiding the consumption of animal products.
Louwman, Marieke WJ et al. Signs of impaired cognitive function in adolescents with marginal cobalamin status. Am J Clin Nut 2000;72:762-769.
For more information please contact Dr. Wija van Staveren at wya.vanstaveren@staff .nutepi.wau.nl
This media release is provided by The American Society for Clinical Nutrition, to provide current information on nutrition-related research. This information should not be construed as medical advice. If you have a medical concern, consult your doctor.
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Journal
American Journal of Clinical Nutrition