Depression Can Be A Pain in the Back

Data available to the research team from the Baltimore wing of the study came from 3,349 subjects in wave one (baseline), 2,747 subjects in wave two, and 1,771 subjects in wave three. Many subjects who participated at baseline participated in wave two, and many of those who participated at baseline and wave two also participated in wave three. Clark and his coworkers were thus in a position to analyze data from a substantial number of subjects both cross-sectionally and longitudinally.

First they attempted to investigate, using the baseline cohort, whether they could link certain factors with a lifetime history of back pain—that is, with a “yes” response to the question, “Have you ever had a lot of trouble with back pain?” The factors included household income, occupation, education, age, body mass index, gender, and a lifetime history of depression. They also attempted to see, using the wave-two cohort, whether they could make similar connections. They did the same again with the wave-three cohort.

Regarding household income, the researchers found no significant link between it and a history of back pain in any of the three cohorts, suggesting that household income probably plays no role in back pain.

Regarding occupations such as heavy lifting or standing or walking for long periods, the investigators did not find a significant link between them and a lifetime history of back pain in the baseline and wave-three cohorts, but they did in the wave-two cohort. This finding suggests that occupations pose only a modest risk for back pain.

As for educational level, the researchers could find no significant association between it and a lifetime history of back pain in the wave-two and wave-three cohorts, but they did in the baseline cohort. Thus, fewer years of education may constitute a modest risk factor for back pain.

Regarding age, the investigators found a significant link between it and a lifetime history of back pain in the baseline cohort and the wave-two cohort, but not in the wave-three cohort, suggesting that age may pose a moderate vulnerability toward back pain.

For body mass index, the researchers found a significant link between it and a lifetime history of back pain in the baseline and wave-three cohorts, but not in the wave-two cohort. Thus, obesity may pose moderate susceptibility toward back pain.

But the biggest risk factors for back pain of all, it seems, are being female and being or having been depressed. The researchers found a highly significant link between being female and having a lifetime history of back pain in all three cohorts, and a highly significant link between a lifetime history of depressive disorder and a lifetime history of back pain in all three cohorts as well.

Now, certainly the highly significant links that Clark and his coworkers found between depression and back pain do not prove that depression causes back pain. It could be the other way around, especially since other researchers have found that depressed persons often experience bodily aches and pains, especially headaches and back pain (Psychiatric News, April 18, 2003).

But Clark and his colleagues suspect that the depression is leading to the back pain, not vice versa, for several reasons. For one, they found that subjects who reported a lifetime history of depressive disorder during both baseline and wave two were over three times more likely to report a first-ever occurrence of back pain during wave three, that is, 13 years later, than were subjects who did not report a lifetime history of depressive disorder at baseline and wave two. (They made this finding while taking some other possibly confounding factors, such as obesity or occupational stress to the back, into consideration.)

For another, they found that having a lifetime history of back pain at baseline was not significantly associated with an increased risk of depression during waves two and three.

Thus, “depressive disorder appears to be a risk factor for incident back pain independent of other characteristics often associated with back pain,” Clark and his coworkers concluded. “[However] back pain is not a short-term consequence of depressive disorder, but emerges over periods longer than one year.”

If these conclusions are valid, they add to the growing evidence that depression helps set the stage for numerous physical illnesses—for example, heart attacks, stroke, type 2 diabetes, breast cancer, even pancreatic cancer (Psychiatric News, November 16, 2001; November 21, 2003).

The study was funded by the National Institute of Mental Health.