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Dementia rate in US significantly declines

Between 2000 and 2012, there was a significant reduction in the number of individuals living with dementia in the United States, according to findings published in JAMA Internal Medicine.

“The aging of the US population is expected to lead to a large increase in the number of adults with dementia, but some recent studies in the United States and other high-income countries suggest that the age-specific risk of dementia may have declined over the past 25 years,” Kenneth M. Langa, MD, PhD, of the division of general medicine at the University of Michigan, and colleagues wrote. “Clarifying current and future population trends in dementia prevalence and risk has important implications for patients, families, and government programs.”

Langa and colleagues evaluated the rate of dementia among individuals aged 65 years or older in the United States by analyzing data from the 2000 (n = 10,546; average age, 75 years; 58.4% female) and 2012 (n = 10,511; average age, 74.8 years; 56.3% female) waves of the Health and Retirement Study. They used a logistic regression model to determine socioeconomic and health factors related to the change in the rate of dementia. The same cognitive measures and diagnostic classification strategy were used in both 2000 and 2012.

Data indicated that among patients aged 65 years and older, the prevalence of dementia declined from 11.6% in 2000 to 8.8% in 2012 (absolute decrease, 2.8%; relative decrease, 24%). More years of education was associated with a decreased risk for dementia. In addition, the researchers found that there was a significant increase in average years of education from 11.8 years in 2000 to 12.7 years in 2012. Obesity was also associated with a lower risk for dementia, while being underweight was associated with an increased risk of dementia.

Despite a substantial age- and sex-adjusted increase from 2000 to 2012 in reported cardiovascular risk factors such as obesity (18.3% vs. 29.2%), diabetes (16.4% vs. 24.7%) and hypertension (54.6% vs. 67.6%), a reduction in dementia rates was still observed.

“Increases in the level of education among the later-born cohort accounted for some of the decreased dementia risk, and there was some evidence that improvements in treatments for cardiovascular risk factors (eg, diabetes) may also have played a role,” Langa and colleagues wrote.

“However, the full set of social, behavioral, and medical factors contributing to the decline in dementia prevalence is still uncertain. Continued monitoring of trends in dementia incidence and prevalence will be important for better gauging the full future societal impact of dementia as the number of older adults increases in the decades ahead, as well as for clarifying potential protective and risk factors for cognitive decline.”

In an accompanying editorial, Ozioma C. Okonkwo, PhD, and Sanjay Asthana, MD, both from the University of Wisconsin School of Medicine and Public Health, wrote that the underlying mechanisms of the associations of education and obesity with dementia reported by this study need to be better understood.

They suggest that diagnostic tests for dementia rely on cognitive performance that is significantly associated with educational attainment.

“Thus, it is possible that the observed association between education and dementia is merely an epiphenomenon of the inherent dependence of test performance on education,” they wrote.

Okonkwo and Asthana pointed to evidence that suggests that the onset of dementia is preceded by weight loss, thereby depleting overall appetite and causing a decrease in the intake of calories; however, they argue that further investigation on the relationship between BMI and dementia is warranted.

“Dementia is undeniably a devastating disease with immense personal and societal costs,” Okonkwo and Asthana concluded. “The growing consistency of reports indicating a potential decrease in its prevalence is encouraging. The focus now should be on better understanding the factors that underlie this trend, and translating that knowledge into interventions that can reduce the risk of dementia for both individuals and the society as a whole.” – by Alaina Tedesco

Disclosure: Langa and colleagues report receiving support from the National Institute of Aging (NIA). Okonkwo and Asthana also report receiving support from the NIA.