Incidence of Dementia and Alzheimer Disease in Nigeria and the United States

To the Editor: While the article by Dr Hendrie and colleagues¹ may be the first to report on geographical differences in Alzheimer disease (AD) incidence, there have been other studies of geographical differences in AD prevalence. The work by White et al² was the first to show that when people of one ethnic group moved from their homeland to the United States, in this case Japanese moving to Hawaii, the AD prevalence increased dramatically. This finding provided the impetus for a multicountry ecologic study of dietary links to AD using data from 11 countries.³ The data were carefully evaluated for comparable methodology and only high-quality reports were included. As a measure of quality, for countries with several reported AD prevalence rates, the data spread was less than 1% unless urban and rural areas or different ethnic groups were studied. The values ranged from 1.4% in Nigeria to 6.2% among African Americans in Indianapolis. This study found that intake of fat and total energy near the time of onset were the strongest risk factors for AD, while consumption of fish reduced the risk. These findings were in accordance with the understanding of oxidative stress and inflammation as risk factors for AD.^4- 5 Additional findings were that the age-adjusted AD prevalence for those aged 65 years or older in the United States was about 5.1% (2.1 ± 0.3 million of all ages).⁵ In particular, the high concentrations of aluminum and transition metal ions and low levels of calcium and magnesium in the brains of those with AD were related to an acid-forming diet, rich in such components as fatty acids and amino acids; and that chronic diseases linked to dietary fat and obesity were highly correlated with the prevalence of AD for the 6 geopolitical regions of the world.