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Lifestyle and Alzheimer disease study strengthens link
African-Americans living in an industrialized US city are more than twice as likely to develop Alzheimer disease and other dementias than are Africans living in Nigeria, according to a study published in the 14 February Journal of the American Medical Association.
The ten-year study, a collaborative effort of researchers from both countries, compared the incidence rates of Alzheimer disease (AD) and other dementias in people over age 65 in Indianapolis, Indiana, in the US, and in Ibadan, Nigeria. A baseline survey identified 2147 African-Americans in Indianapolis and 2459 Yoruba residents of Ibadan who did not have dementia. Follow-up studies at 2 and 5 years found that 2.52% of the African-Americans eventually developed AD, compared to only 1.15% of the Yoruba; overall, 3.24% of the African-Americans developed any formof dementia (including AD), compared to 1.35% of the Yoruba. The rates found among the African-Americans are in the higher range of previously published rates, while the rates found in the Yoruba are among the lowest, reported the studys principal investigators, Dr Hugh C. Hendrie of the University of Indiana School of Medicine in the US and Dr Adesola Ogunniyi of the University of Ibadan.
The researchers did not draw conclusions as to why the disease rates varied, but postulated two factors: genetics and lifestyle. They found that a gene (apolipoprotein E), known to raise the risk of Alzheimer disease, occurred with equal frequency in the two groups. However, in the African-Americans the gene is definitely increasing the risk for Alzheimer disease, while in the Nigerian group it doesnt seem to have an effect, Dr Frederick W. Unverzagt, a co-author of the study, told the Bulletin. As for possible lifestyle influences, the study found that the Yoruba have a much lower prevalence of vascular risk factors lower cholesterol levels and fewer cases of diabetes and hypertension than the African-Americans.
Maybe the incidence numbers can be explained by a geneenvironment interaction, says Unverzagt. It could be that the ApoE gene is just not activated in certain environments. Follow-up studies, he says, will examine diet, activity levels, and social engagedness. If factors like diet are found to influence the disease, says Unverzagt, the public health implications could be tremendous. If modifying such factors could delay the onset of Alzheimer by 5 to 10 years, you could really forestall some of the looming public health problems posed by the disease.
The study is believed to be the first cross-cultural study of dementia to use the same methodology and the same group of researchers at different sites. Previous studies have compared rates from different countries, but drawing conclusions from such comparisons is often difficult because of methodological differences.
Such cross-cultural studies are extremely difficult to do, Dr Denis Evans, director of the Rush Institute for Healthy Aging, in Chicago, commented to the Bulletin. Theyve done a magnificent job with that. They carried out the same procedures 4000 miles apart. This is very encouraging for people who have thought about doing this sort of work.
In an accompanying editorial, Dr Lindsay Farrer of the Boston University School of Medicine, Massachusetts, says preliminary evidence suggests that a high-fat diet may increase the risk of developing Alzheimer disease and studies have revealed that [Alzheimer] cases are less active physically than controls in early life. Currently, though, most experts say that the only established risk factors are genetics and increasing age. 
Catherine Dold,
Boulder, Colorado, USA