TABLE 1.

Lifebrain eligible study cohorts: sample sizes and waves of assessment for each measure of loneliness, episodic memory, and magnetic resonance imaging (MRI).

Study cohort (city/country) and sample characteristics	Loneliness (N: sample size for each time point)	Memory (N: sample size for each time point)	MRI image (T1) (N: sample size for each time point)
BETULA (Umeå/Sweden): aged 60–85 (Nilsson et al., 1997).	Four time-points (N = 143, 185, 260, and 250). Interval period: 5 years.	Four time-points (N = 143, 185, 260, and 250). Interval period: 5 years.	Two time-points of MRI (N = 230 and 168). Interval period: 4 years.
BASE-II (Berlin/Germany): aged 60–86 (Bertram et al., 2014).	Three time-points (N = 1325, 219, and 844). Mean interval periods ranging from 2.3 to 3.23, with a mean of 5.54 years (SD 0.45) between first and last assessment.	Three time-points: (N = 1323, 218, and 749). Mean interval periods ranging from 2.3 to 3.24, with a mean of 5.57 (SD 0.45) between first and last assessment.	Two time-points (N = 215 and 215). Mean interval period: 2.29 years (SD 0.45)
HUBU (Copenhagen/Denmark): aged 10–15 (Madsen et al., 2018).	Four time-points (N = 69, 68, 59, and 39). Mean interval periods from 1.11 to 1.34, with a mean interval period of 3.43 years (SD 0.43) between first and last assessment.	Two time-points (N = 59 and 31). Mean memory interval period: 4.04 (SD 0.23).	Four time-points (N = 66, 64, 42, and 38). Mean interval periods from 1.08 to 1.35, with a mean interval period of 3.42 years (SD 0.45) between first and last MRI.