Does Tobacco Smoking Increase Social Isolation? A Mendelian Randomization Study

This study aimed to investigate the causal effect of smoking on social isolation among older adults in England. Data from older adults of European ancestry who participated in one or more waves from wave 1 (2002/2003) to 9 (2018/2019) of the English Longitudinal Study of Ageing were analyzed (n = 43,687 observations from 7,008 individuals; mean age 68.50). The effect of current smoking on social isolation (ranges from 0 to 5) was estimated by two-stage least squares estimation using a polygenic score (PGS) for smoking cessation as the instrument. A low PGS for smoking cessation predicted current smoking (coefficient per 1 standard deviation = 0.023; 95% confidence interval, CI: 0.015, 0.030; F = 36.420). The second-stage regression showed that current smoking increased social isolation by 1.205 points (95% CI: 0.308, 2.101). The association was larger for those with higher socioeconomic backgrounds: 2.501 (95% CI: -0.024, 5.026) and 0.696 (95% CI: -0.294, 1.686) for those with higher and lower education, respectively. This study showed that current smoking instrumented by the PGS for smoking cessation was associated with social isolation. Assuming that the PGS served as a valid instrument in this study, the findings support the effect of smoking on social isolation.