Genetic factors help to explain the common association between low back pain and depression, according to a large study of twins published in the March issue of Pain.
Marina B. Pinheiro, MSc, and her research colleagues at the University of Sydney in Australia, analyzed data from the Murcia Twin Registry of nearly 2,150 Spanish twins. Questionnaire responses were assessed to determine whether participants with symptoms of depression had a higher prevalence of back pain. A series of statistical analyses were then performed to clarify genetic factors and to determine how an environment that is shared early on can contribute to the linkage between depression and back pain.
Marina B. Pinheiro, MSc
The results showed a significant association between symptoms of depression and low back pain. On the initial analysis, which considered the participants as individuals, the odds of having back pain were about 1.6 higher for those with symptoms of depression and anxiety.
For the analysis of twin pairs, which controlled for genetic and familial factors that could influence the relationship between depression and back pain, there was a 1.7 increase in odds. The association was even stronger—more than a 2.3 increase in odds of low back pain associated with depression and anxiety—on the analysis of dizygotic twins.
Upon further analysis of monozygotic twins, the association between symptoms of depression and low back pain disappeared. This suggested that the strong association found in non-identical twins resulted from the confounding effects of common genetic factors influencing both conditions.
Overall, the finding that the association between symptoms of depression and low back pain disappears after fully adjusting for genetics and familial confounders in identical twins suggests that genetics is the main confounder of the relationship between depression and back pain.