Abstract
Levels of activity are often affected in psychiatric disorders and can be core symptoms of illness. Advances in technology now allow the accurate assessment of activity levels but it remains unclear whether alterations in activity arise from shared risk factors for developing psychiatric disorders, such as genetics, or are better explained as consequences of the disorders and their associated factors. We aimed to examine objectively-measured physical activity in individuals with psychiatric disorders, and assess the role of genetic liability for psychiatric disorders on physical activity. Accelerometer data were available on 95,529 UK Biobank participants, including measures of overall mean activity and minutes per day of moderate activity, walking, sedentary activity, and sleep. Linear regressions measured associations between psychiatric diagnosis and activity levels, and polygenic risk scores (PRS) for psychiatric disorders and activity levels. Genetic correlations were calculated between psychiatric disorders and different types of activity. Having a diagnosis of schizophrenia, bipolar disorder, depression, or autism spectrum disorders (ASD) was associated with reduced overall activity compared to unaffected controls. In individuals without a psychiatric disorder, reduced overall activity levels were associated with PRS for schizophrenia, depression, and ASD. ADHD PRS was associated with increased overall activity. Genetic correlations were consistent with PRS findings. Variation in physical activity is an important feature across psychiatric disorders. Whilst levels of activity are associated with genetic liability to psychiatric disorders to a very limited extent, the substantial differences in activity levels in those with psychiatric disorders most likely arise as a consequences of disorder-related factors.
Highlights
Estimates suggest that physical inactivity causes 9% of premature mortality and 6–10% of the major non-communicable diseases worldwide [1]
Individuals with a diagnosis of schizophrenia, bipolar disorder, depression, attention deficit hyperactivity disorder (ADHD), or autism spectrum disorders (ASD) were significantly less likely to participate than individuals without a mental health disorder (OR = 0.95; 95% CI = 0.92, 0.98; p = 0.002)
A total of 95,744 participants were included in the study with high quality accelerometer data (56.4% female, mean age at recruitment [standard deviations (SD)] 56.2 [7.8], see S2 Fig). 6,527 individuals were classified as having depression, 466 with bipolar disorder, 95 with schizophrenia, 87 with ASD, and 53 with ADHD
Summary
Estimates suggest that physical inactivity causes 9% of premature mortality and 6–10% of the major non-communicable diseases worldwide [1]. Studies of physical activity have predominantly relied on self-report measures but this may lead to unreliable estimates of activity, especially for those with mental illness. A recent study reported marked differences when comparing accelerometer-measured activity between individuals with schizophrenia and controls, but not for self-reported activity [12]. This suggests that objective measures may better characterise physical activity in individuals with mental health disorders, and such approaches are being considered as part of clinical psychiatric care [13]. Research using accelerometers in the UK Biobank has shown physical activity to be a polygenic trait, with a heritability of around 23% in women and 20% in men [14]
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