A large number of older adults in low-income settings are currently experiencing sleep problems, which emphasizes the global dimension of this emerging public health issue. This study corroborates the multifaceted nature of sleep problems, which are strongly linked to poorer general well-being and quality of life, and psychiatric comorbidities.

Population ageing is a global phenomenon. The United Nations estimates that the world population aged over 60 will have increased 3-fold from 1950 to 2050, to reach 21% of the population. 1 This compositional shift is happening fastest in low-and middle-income countries (LMIC). 2 South Africa in particular is undergoing a dramatic demographic and epidemiological transition, and little is known about the socioeconomic determinants or consequences of transition. This study, following important findings in previous studies in Agincourt 3-6 and South Africa in general, 7-9 is set up to inform us about morbidity, mortality and aetiological factors shaping these trends. Various ageing studies, including the Studies on Global Ageing and Adult Health (SAGE) and the 2015 Global Burden of Disease, found that noncommunicable diseases, driven mainly by population growth and ageing, have become leading causes of death and disability globally, including in LMIC such as South Africa. 10-14 At the same time, the share of the population 60 and above in South Africa is estimated to increase from 7.8% in 2012 to 14.8% in 2050, 15 and the population aged 50 and over living with HIV will triple by 2040. 16 We established the cohort 'Health and Ageing in Africa: A Longitudinal Study of an INDEPTH Community' in South Africa (HAALSI) in the INDEPTH Health and Demographic Surveillance System (HDSS) site of Agincourt, as a harmonized sister study to the Health and Retirement Study (HRS) in the USA 17 and other similar studies worldwide, including ELSA in the UK, 18