Background Previous studies have explored the association between social media use and mental health among adolescents. However, few studies using nationally representative longitudinal data have explored this relationship for adults and how the effect might change depending on how people use social media.This study investigated the longitudinal relationship between the frequency of viewing and posting on social media and mental health problems among UK adults.

Methods This study included 15,836 adults (aged 16-years old or above) who participated in Understanding Society (USoc), a UK longitudinal survey. Social media use was measured with questions about frequency of viewing and posting on social media in USoc Wave 11 (2019-2021). We explored viewing and posting separately and as a combined exposure: (1) high viewing, high posting; (2) high viewing, low posting; (3) low viewing, high posting; and (4) low viewing, low posting. Mental health problems were measured by the General Health Questionnaire (GHQ-12) in USoc Wave 12 (2020-2022). Unadjusted and adjusted linear regression models were estimated for viewing social media and posting on social media, adjusting for sex, age, ethnicity, employment, and education. We also explored the data for effect modification by sex and age but found no evidence for effect modification so overall associations were reported.

Results In our adjusted models, we found no evidence of an association between frequency of viewing social media and mental health problems in the following year. We found that adults who posted daily on social media had more mental health problems than those who never posted on social media (coef.=0.35, 95% CI: 0.014-0.68, P=0.04). When we considered both social media behaviours, we found that those who frequently viewed and posted on social media had more mental health problems a year later than those who rarely viewed or posted on social media (coef.=0.31, 95% CI: 0.04-0.58, P=0.03).

Conclusion We found that a high frequency of posting on social media was associated with increased mental health problems a year later. However, we did not find evidence of a similar association based on frequency of viewing social media content. This provides evidence that some types of active social media use (i.e. posting) have a stronger link to mental health outcomes than some types of passive social media use (viewing). These results highlighted that the relationship between social media use and mental health is complex, and more research is needed to understand the mechanisms underlying these patterns to inform targeted interventions and policies.