Research published in The Lancet Healthy Longevity provides evidence to support that living with others, community group engagement and never feeling lonely are associated with slower cognitive decline.

It is widely recognized that poor social connections such as small networks, infrequent interactions, and loneliness are modifiable risk factors for cognitive decline, with the 2020 Lancet Commission on dementia prevention estimating that tackling social isolation could prevent 4% of dementia cases worldwide.

However, up until now research hasn't examined data beyond North America and Europe. Existing research has also combined variables indicating good social connections (such as living with others and being married) instead of looking at each one separately. This means that we couldn't say what exact type or amount of social connections we need for healthy brain ageing.

This research, led by UNSW Sydney's Centre for Healthy Brain Aging (CHeBA), investigated a range of measures of social connectedness to discover which had the most robust findings in relation to risk reduction of cognitive decline—and dementia.

"We looked at a range of measures of social connections, in approximately 40,000 people across 13 international studies," says lead author Dr. Suraj Samtani, Postdoctoral Fellow and social health expert at CHeBA. "Previous analyses of multiple international studies have many limitations.

"Our goal was to investigate the association between various social connection markers and the rate of annual change in cognition. We had longitudinal data from six continents, making this the most representative analysis done on social connections and cognitive decline until now. We also examined each social connection variable individually to compare their impacts on cognitive decline."

Co-author and CHeBA Co-Director Professor Henry Brodaty said that the findings have socio-economic significance. "We found that sharing a home with one or more person[s] and weekly community group engagement had the most robust results across studies, indicating these factors are fundamental components in the link with less cognitive decline," says Professor Brodaty. "We also identified an association between never feeling lonely and a slower rate of cognitive decline."

The researchers did not find a significant association between degree of social support, having a confidante or relationship satisfaction and cognitive decline.

"The data from 13 international studies was accessible as a result of The Dementia Momentum," says a spokesman for the initiative, Dr. Richard Grellman AM. "The ageing studies for this particular research originated from North and South America, Europe, Africa, Asia and Australia and are part of the Cohort Studies of Memory in an International Consortium—or COSMIC."

COSMIC Consortium Leader Professor Perminder Sachdev says that "having researchers of brain aging from around the world come together in this collaboration to determine what factors of social connection are common for memory decline will have significant impact on policy change for the future of Alzheimer's disease and other dementias."

Future research will be important to replicate these findings, and crucially, to determine if interventions at individual or societal levels can improve social connectedness and alleviate loneliness.