CHICAGO -- August 7, 2008 -- Voluntary physical activity does not appear to cause a reduction in anxiety and depression, but exercise and mood may be associated through a common genetic factor, according to a study in the August issue of Archives of General Psychiatry.
Marleen H. M. De Moor, VU University Amsterdam, Amsterdam, Netherlands, and colleagues, studied 5,952 twins from the Netherlands Twin Register, along with 1,357 additional siblings and 1,249 parents.
Participants, all aged 18 to 50 years, filled out surveys about leisure-time exercise and completed 4 scales measuring anxious and depressive symptoms.
Associations observed between exercise and anxious and depressive symptoms "were small and were best explained by common genetic factors with opposite effects on exercise behaviour and symptoms of anxiety and depression," said the authors.
"In genetically identical twin pairs, the twin who exercised more did not display fewer anxious and depressive symptoms than the co-twin who exercised less." Exercise behaviour in one identical twin predicted anxious and depressive symptoms in the other, meaning that if one twin exercised more, the other tended to have fewer symptoms.
However, the same was not true of dizygotic twins or other siblings, who share only part of their genetic material. In addition, analyses over time showed that individuals who increased their level of exercise did not experience a decrease in anxious and depressive symptoms.
The results do not mean that exercise cannot benefit those with anxiety or depression, the authors noted, only that additional trials would be needed to justify this type of therapy.
"Only voluntary leisure-time exercise is influenced by genetic factors, whereas the other type of exercise is environment-driven. The absence of causal effects of voluntary exercise on symptoms of anxiety and depression does not imply that manipulation of exercise cannot be used to change such symptoms," they wrote.
"The antidepressant effects of exercise may only occur if the exercise is monitored and part of a therapeutic program."
SOURCE: Journal of the American Medical Association
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