A new study published in The BMJ has brought to light a complex and nuanced picture of dementia in the United States. Between 2015 and 2021, the rate of new dementia diagnoses—known as incidence—declined among Americans aged 66 and older. Yet, the number of people living with the condition has steadily risen. This finding reflects a tension between improved disease prevention on the one hand and an ageing population on the other. In 2021 alone, nearly 2.9 million individuals enrolled in traditional Medicare—roughly 12%—were living with a diagnosis of dementia, underscoring the growing impact of this condition on the nation’s healthcare landscape.
Drawing upon an extensive dataset of medical claims for over 5 million fee-for-service Medicare beneficiaries, the researchers noted that incidence fell from 3.5% to 2.8% over the six years. At the same time, prevalence—the proportion of people living with dementia—rose from 10.5% to 11.8%. This paradox reveals an essential aspect of dementia care: even as fewer people are newly diagnosed each year, more people than ever before are living longer lives with the disease. The researchers attribute the decline in new cases partly to improved management of cardiovascular risk factors, which play a significant role in dementia development. However, the ageing of the population means that more people are surviving long enough to experience dementia or are living longer after a diagnosis has been made.
Interestingly, the data reveal subtle yet telling differences between the sexes. In 2015, the incidence of dementia was slightly higher among men (3.5%) than women (3.4%) of the same age, and this gap widened by 2021, with men at 2.9% and women at 2.6%. Yet, paradoxically, the majority of people living with dementia are women—60% of those diagnosed in 2021. The authors explain this by pointing to women’s longer life expectancy, which means that more women live in the age range where dementia risk is highest. As such, while men may face a higher annual risk of developing dementia, the overall burden of the condition weighs more heavily on women in later life.
The study also highlights stark and persistent inequalities in dementia risk among different racial and ethnic groups, as well as across neighbourhoods marked by socioeconomic deprivation. Black beneficiaries had the highest incidence of dementia throughout the period, with 4.2% newly diagnosed in 2015 and 3.1% in 2021. Hispanic beneficiaries followed, with rates of 3.7% and 2.6%, respectively. White beneficiaries had the lowest rates in both years. These disparities underscore how social determinants of health—factors such as income, education, and access to healthcare—play a profound role in shaping the dementia burden across communities.
The authors point out that the reasons behind these racial and socioeconomic disparities are complex and multifaceted. It is possible that structural factors, such as historical discrimination and unequal access to healthcare resources, contribute to higher dementia incidence in marginalised populations. Furthermore, those living in deprived neighbourhoods may face more cumulative risks—poorer nutrition, higher rates of cardiovascular disease, and fewer opportunities for healthy ageing—which in turn elevate dementia risk. Addressing these underlying causes, the researchers argue, is essential to promoting health equity in dementia care.
Notably, the researchers also caution that their robust findings should be interpreted with care. As an observational study, their work does not establish direct cause-and-effect relationships. Moreover, Medicare claims data may not perfectly capture diagnoses or may fail to account for individuals who do not have fee-for-service Medicare coverage. The data also have limitations in accurately classifying race and ethnicity, which means that the true extent of disparities could be even greater than reported. Nevertheless, the sheer size and scope of the dataset provide valuable insights into real-world diagnostic patterns and help fill an essential gap in the medical literature.
An accompanying editorial by UK researchers echoes these concerns, noting that marginalised minorities are often under-represented in fee-for-service Medicare plans. This under-representation suggests that the actual burden of dementia in disadvantaged groups could be even more significant than the current data show. Furthermore, greater health awareness and earlier diagnoses in wealthier communities might mask the true magnitude of the socioeconomic divide. Taken together, these findings highlight the pressing need for improved services for those living with dementia, particularly in areas where higher incidence and prevalence are observed, and for policy initiatives aimed at addressing risk factors and inequalities from early life onwards.
More information: Jay B Lusk et al, Incidence and prevalence of dementia among US Medicare beneficiaries, 2015-21: population based study, The BMJ. DOI: 10.1136/bmj-2024-083034
Journal information: The BMJ Provided by BMJ Group
