Policymakers and researchers have little evidence on prevalence rates of intellectual disability (ID) or their changes over time to tailor healthcare interventions. Prevalence rates and trends of ID are especially lacking in regions with lower socio-demographic development. Additionally, the assessment of inequalities in the prevalence of ID across regions with varying socio-demographic development is understudied. This study assessed variations in prevalence rates of ID from 1990 to 2019 and the related inequalities between low and high socio-demographic index (SDI) regions.

This study used global data from 1990 to 2019 for individuals with ID from the 2019 Global Burden of Diseases study. Data analyses were performed from September 2021 to January 2022. Prevalence for individuals with ID was extracted by sex, age groups and SDI regions. Annual percentage change (APC) was estimated for each demographic group within SDI regions to assess their prevalence trends over 30 years. Relative and absolute inequalities were calculated between low and high SDI regions for the various age groups.

In 2019, there were 107.62 million (1.74%) individuals with ID, with an APC of −0.80 (−0.88 to −0.72). There was a slightly higher prevalence among males (1.42%) than females (1.37%). The highest prevalence rates were found in the low-middle SDI regions (2.42%) and the lowest prevalence rates were in the high SDI regions (0.33%). There was a large reduction in the prevalence rate between the youngest age group v. the oldest age group in all the SDI regions and at all time points. The relative inequalities between low and high SDI regions increased over three decades.

While an overall decrease in global prevalence rate for ID was found, relative inequalities continue to increase with lower SDI regions needing more comprehensive support services. The demographic trends indicate a significantly higher mortality rate among those with ID v. the rest of the population. Our study highlights the necessity for policies and interventions targeting lower SDI regions to mobilise resources that better support individuals with ID and achieve sustainable development goals proposed by the United Nations.