1. United Nations. Department of Economic and Social Affairs Population Division (ST/ESA/SER.A/430). United Nations World Population Ageing 2019. Highlights. United Nations, NY (2019). https://www.un.org/en/development/desa/population/publications/pdf/ageing/WorldPopulationAgeing2019-Highlights.pdf
2. United Nations. Department of Economic and Social Affairs Population Division (ST/ESA/SER.A/423). United Nations World Population Prospects 2019: Highlights United Nations, NY (2019). https://population.un.org/wpp/Publications/Files/WPP2019_Highlights.pdf
3. United Nations. Department of Economic and Social Affairs, Population Division (ST/ESA/SER.A/390). United Nations World Population Ageing 2015. Highlights. United Nations, NY (2015). https://www.un.org/en/development/desa/population/publications/pdf/ageing/WPA2015_Highlights.pdf
4. World Health Organization: Social isolation and loneliness among older people: advocacy brief. World Health Organization, Geneva: License: CC BY-NC-SA 3.0 IGO (2021)
5. Fried, L., Tangen, C., Walston, J., Newman, A., et al.: (Cardiovascular Health Study Collaborative Research Group): Frailty in older adults: evidence for a phenotype. J. Gerontol. A Biol. Sci. Med. Sci. 56(3), M146–M156 (2001). https://doi.org/10.1093/gerona/56.3.m146