An analysis of the global burden and temporal trends of Alzheimer’s disease and other dementias (ADODs) reveals significant cross-country inequalities associated with a series of sociodemographic development-related risk factors, such as education, income, fertility, and health expenditure. The new study in the American Journal of Preventive Medicine, published by Elsevier, calls for the development of targeted prevention and control strategies in different countries.

The burden of ADODs has risen globally over the past three decades. The authors of this first systematic and comprehensive global study analyzing data from 1990 to 2021, including data from the Global Burden of Disease 2021 study and the World Bank, found that there are significant disparities in numbers, rates, and age-standardized rates of disability-adjusted life years across 204 countries and territories. 

Lead investigator Ya Fang, MD, PhD, School of Public Health, Xiamen University, China, says, “ADODs currently pose a major global public health challenge. They stand as a leading cause of functional loss and dependence among older individuals worldwide. Yet, to date, there are no definitive treatments capable of fully resolving ADODs. Furthermore, research exploring the relationship between sociodemographic development-related factors and health inequalities associated with ADODs is currently limited. Therefore, we aimed to establish this connection by assessing the impact of sociodemographic development indicators such as education, income, fertility, and health expenditure on ADODs health metrics.”

The study found that approximately two-thirds of individuals with ADODs worldwide now live in low- and low-middle income countries, and as populations grow, the number of cases with ADODs in these countries is expected to rise faster than in high-income countries. Therefore, the disease burden of ADODs is believed to be greater in low- and middle-income countries, where individuals are more likely to face poverty and limited access to healthcare. However, even in countries with high sociodemographic development levels, such as Luxembourg, Switzerland, and the United States, despite having relatively comprehensive healthcare systems, the disease burden of ADODs remains high because of the specific distribution of ADOD risk factors in these countries, such as obesity, poor diet, and diabetes.

Another noteworthy finding is that females exhibited a notably higher burden of ADODs than males across all age groups, corroborating previous research that identifies female sex as a risk factor for accelerated cognitive decline. Gender differences in disease may be influenced by reproductive capacity, sex hormones, genetic predisposition, and epigenetics. Females are especially sensitive to hormonal fluctuations, particularly during premenstrual, perinatal, and menopausal periods. Estradiol and progesterone fluctuations during pregnancy impact maternal brain structure and function, such that the reproductive history of women may affect brain aging and disease risk.

This study integrated the Global Burden of Disease 2021 and World Bank data, and to the authors’ knowledge is the first systematic and comprehensive study on cross-country inequality associated with a series of sociodemographic development-related factors. Other significant strengths of this study are its long observation period, wide geographical range, and extensive data coverage. Based on the results, it is necessary to further control risk factors of ADODs by promoting a healthy diet and regular exercise for preventing the development of ADODs in developed countries. However, enhancing basic healthcare, improving medical resource access and affordability, and raising ADOD awareness among the public in developing countries are also vital.”

Ya Fang, MD, PhD, School of Public Health, Xiamen University