Introduction: For almost a century, a considerable number of studies reporting associations between intelligence and religiosity have accumulated. However, reported effect size strengths vary substantially between primary studies. This heterogeneity has partly been attributed to measurement modalities. Associations with intelligence tend to be more pronounced for religious beliefs than for religious behaviors. Another factor potentially adding to the heterogeneity is participant age. Evidence suggests a protective effect of religiosity against cognitive declines in older ages. This indicates a decrease in the effect strength of the intelligence and religiosity link over a lifetime. However, these protective effects have been only observed in comparatively religious countries.
Methods: Here, we examine cross-sectional correlations of religiosity and cognitive functions as well as their cross-temporal changes across cohorts over a period of 10 years in European and Israeli participants aged 50+ years (N = 30,424) using the Survey of Health, Ageing, and Retirement in Europe.
Results: We observed meaningful negative associations of all measures of cognitive function and a composite score with religious beliefs (r = -.107). However, associations with religious behavior were negligible (r = .014). Effects appeared to generalize across age, thus contrasting the idea of age-related declines of effect strength in our data.

Conclusions: We presently demonstrate that intelligence is negatively associated with religiosity in elderly European samples. These associations remained stable over increasing participant ages and therefore do not support previous findings suggesting protective effects of religiosity against cognitive declines.