Abstract
Alzheimer’s disease (AD) is a progressive degenerating disease of complex etiology. A variety of risk factors contribute to the chance of developing AD. Lifestyle factors, such as physical, mental and social activity, education, and diet all affect the susceptibility to developing AD. These factors are in turn related to the level of personal income. Lower income usually coincides with lower level of education, lesser mental, leisure—social and physical activity, and poorer diet. In the present paper, we have analyzed the correlation of historical (1929–2011) per capita personal income (PCPI) for all states of the USA with corresponding age-adjusted AD death rates (AADR) for years 2000, 2005 and 2008. We found negative correlations in all cases, the highest one (R ≈ -0.65) for the PCPIs in the year 1970 correlated against the AADRs in 2005. From 1929 to 2005 the R value varies in an oscillatory manner, with the strongest correlations in 1929, 1970, 1990 and the weakest in 1950, 1980, 1998. Further analysis indicated that this oscillatory behavior of R is not artificially related to the economic factors but rather to delayed biological consequences associated with personal income. We conclude that the influence of the income level on the AD mortality in 2005 was the highest in the early years of life of the AD victims. Overall, the income had a significant, lifelong, albeit constantly decreasing, influence on the risk of developing AD. We postulate that the susceptibility of a population to late-onset AD (LOAD) is determined to a large extent by the history of income-related modifiable lifestyle risk factors. Among these risk factors, inappropriate diet has a significant contribution.
Highlights
The prevalence of Alzheimer’s disease (AD) is steadily increasing worldwide, including the USA [1,2,3]
How, the per capita personal income (PCPI), presumably by affecting the lifestyle, has an influence on the AD mortality, we studied the correlation of PCPI for each state of the USA, starting from the year 1929, just before the Great Depression, through the year 2011, with age-adjusted AD death rates (AADRs) for those states in 2000, 2005 and 2008
The death rates for other years from the period 2000–2011 correlated with the 1970 PCPIs less strongly than did the 2005 AADRs (Fig 2)
Summary
The prevalence of Alzheimer’s disease (AD) is steadily increasing worldwide, including the USA [1,2,3]. The reasons for such a profound increase in the number of AD cases are unclear. In order to elucidate the causes of this increase, risk factors present in the history of a population should be considered. Among known factors increasing the risk of developing Alzheimer’s disease the most important one is the aging of the population [4,5]. Alzheimer’s disease is PLOS ONE | DOI:10.1371/journal.pone.0126139. Alzheimer’s disease is PLOS ONE | DOI:10.1371/journal.pone.0126139 May 11, 2015
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