Sitting-time, physical activity, and depressive symptoms in mid-aged women

American Journal of Preventive Medicine, 09/20/2013

van Uffelen JGZ et al. – The study aims to examine concurrent and prospective associations between both sitting–time and physical activity with prevalent depressive symptoms in mid–aged Australian women. Increasing physical activity to a level commensurate with guidelines can alleviate current depression symptoms and prevent future symptoms in mid–aged women. Reducing sitting–time may ameliorate current symptoms.

Methods

  • Data were from 8950 women, aged 50–55 years in 2001, who completed mail surveys in 2001, 2004, 2007, and 2010.
  • Depressive symptoms were assessed using the Center for Epidemiological Studies Depression questionnaire.
  • Associations between sitting-time (≤4 hours/day, >4–7 hours/day, >7 hours/day) and physical activity (none, some, meeting guidelines) with depressive symptoms (symptoms/no symptoms) were examined in 2011 in concurrent and lagged mixed-effect logistic modeling.
  • Both main effects and interaction models were developed.

Results

  • In main effects modeling, women who sat >7 hours/day (OR=1.47, 95% CI=1.29, 1.67) and women who did no physical activity (OR=1.99, 95% CI=1.75, 2.27) were more likely to have depressive symptoms than women who sat ≤4 hours/day and who met physical activity guidelines, respectively.
  • In interaction modeling, the likelihood of depressive symptoms in women who sat >7 hours/day and did no physical activity was triple that of women who sat ≤4 hours/day and met physical activity guidelines (OR 2.96, 95% CI=2.37, 3.69).
  • In prospective main effects and interaction modeling, sitting-time was not associated with depressive symptoms, but women who did no physical activity were more likely than those who met physical activity guidelines to have future depressive symptoms (OR=1.26, 95% CI=1.08, 1.47).

Author Commentary

An interesting finding in our study was that sitting-time was associated with current depressive symptoms, but not with future symptoms. There are several potential explanations for this, which are described in more detail in the article. A particularly interesting explanation is the potential of reverse causality. Fatigue and loss of energy are common depressive symptoms and it could therefore be the case that, instead of high sitting-time causing depressive symptoms, depressive symptoms cause high sitting-time. Although this seems to be a logical explanation, we did not find evidence for reverse causation in our study. For a 6 minute video cast of the paper, please see: http://www.scivee.tv/node/60419

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