The relationship between handgrip strength and cognition in major depression, bipolar disorder and healthy controls: a population-scale analysis of 110,067 individuals

Importance: Objective physical fitness measures, such as handgrip strength, are associated with physical, mental and cognitive outcomes in the general population. Although people with mental illness experience reduced physical fitness and cognitive impairment, the relationship between these areas has not been examined. Objective: To determine relationships between maximal grip strength and cognitive performance in major depression, bipolar disorder and healthy controls. Design: Cross-sectional analysis of baseline data from over 110,000 participants of the UK Biobank. Setting: Multi-centre, population-based study conducted between 2007-2010 in the UK. Participants: Invitations were mailed to 9.2 million U.K. homes, recruiting 502,664 adults, all aged 37 – 73 years. Clinically-validated measures were used to identify individuals with major recurrent depression (moderate or severe), bipolar disorder (type I or type II) and ‘healthy controls’ (with no indication of present or previous mood disorders). Main Outcome(s) and Measure(s): Handgrip dynamometry was used to measure muscular function. Cognitive functioning was assessed using computerized tasks of reaction time, visual memory, number memory, reasoning and prospective memory. Generalised linear mixed models assessed the relationship between grip strength and cognitive performance, controlling for age, education, gender, bodyweight and geographical region. Results: Analyses included 22,699 individuals with major depression (age=55.5, 35% male), 1,475 with bipolar disorder (age=54.4, 51% male) and 85,895 healthy controls (age=53.7, 50% male). In those with major depression, significant positive relationships (p<0.001) between maximal grip strength and improved performance on all five cognitive tasks were found: including visual memory (coeff=-0.146, S.E.=0.014), reaction time (coeff= -0.036, S.E.=0.002), reasoning (coeff=0.213, S.E.=0.02), number memory (coeff=0.160, S.E.=0.023) and prospective memory (coeff=0.341, S.E.=0.024). Similar results were found in healthy controls. Among those with bipolar disorder, grip strength was positively associated with improved visual memory (coeff=-0.129, S.E. =0.052, p=0.013), reaction time (coeff=-0.047 S.E.=0.007, p<0.001), prospective memory (coeff=0.262, S.E.=0.088, p=0.003) and reasoning (coeff=0.354, S.E.=0.080, p<0.001). Conclusions and Relevance: Grip strength may provide a useful indicator of cognitive impairments in people with major depression and bipolar disorder. Future research should investigate causality, assess the functional implications of grip strength in psychiatric populations, and examine how interventions to improve muscular fitness impact on neurocognitive status and socio-occupational functioning.