by Diana Swift
Medpage Today

Weight and depression were independent predictors of an increase in back pain risk, according to a Australian study.

Among women with a median age of 49.5 who were followed at 3-year interval over 15 years, for every 5 kg of higher weight at baseline participants had a 7% (95% CI 6%-8%) higher odds of back pain after adjusting for age, height, employment status, depression, vigorous physical activity, and menopausal and smoking status (P<0.001), reported Flavia M. Cicuttini, PhD, of Monash University in Melbourne, and colleagues.

Also, being diagnosed with depression was associated with a 37% increased risk of back pain over the following 15 years, after adjustment for the above confounders including weight (both P<0.001), they wrote in Arthritis Care & Research.

However, engaging in any vigorous leisure physical activity significantly reduced risk, the authors noted.

"Even though the magnitude of the increased risk of back pain in this study was small, the significant burden of back pain on a population level means that these risk factors could potentially have a large impact," Cicuttini's group wrote.

The study cohort consisted of women born during 1946-1951 and randomly selected from Australia's national health insurance scheme database to participate in the long-term Australian Longitudinal Study of Women's Health.

Participants were surveyed on the frequency of their back pain in the past 12 months every 3 years from 1998 to 2013. In the first survey, 12,338 women responded while 10,011 (74%) responded in 2013 to the final survey. Back pain was common, with 54% reporting it in 1998 and 59.6% in the final survey in 2013. The effects of weight on back pain were most marked in those with a body mass index of ≥25 kg/m2.

At baseline, back pain sufferers were somewhat heavier; more likely to have been diagnosed with depression; more likely to be peri- or postmenopausal; more likely to be current smokers; and less likely to participate in vigorous leisure activity. The proportion doing inadequate levels of physical activity (<600 MET.mins/week) did not significantly differ between these two groups. Those with back pain were more likely to have a low level of education, less likely to be doing paid work, and less likely to be working more than 35 hours per week.

Women gained a mean of 1.4 kg between the baseline and second survey 3 years later and a mean of 4.1 kg across the entire 15-year study period. For every 1.4 kg of weight gain from baseline to the second survey, there was a 1% (95% CI 1%-2%) increased risk of back pain over the following 12 years.

The predictive effects of weight gain persisted, despite the cohort's average gain of only 4.1 kg over 15 years.

But participation in vigorous ("puff and pant") physical activity at baseline was associated with an encouraging 19% reduced risk of back pain.

The authors observed that while obesity and depression are acknowledged risk factors for back pain, interactions between these risks have received scant research attention. Physical activity may also impact both depression and weight, and therefore indirectly on back pain.

"To date few studies have examined these modifiable predictors of back pain in middle-aged women, with exposure and outcome measures assessed at multiple time points; hence major inconsistency and knowledge gaps persist in this area," the investigators wrote.

"Although clinical intervention trials are required, strategies that target weight, lack of physical activity and mental health may be important in the prevention of back pain in middle-aged women," they stated.

A study limitation was that weight and physical activity levels were self-reported.

David G. Borenstein, MD, of Arthritis and Rheumatism Associates in Washington, praised the study for its protracted Framingham Study-like follow-up that puts in perspective the often conflicting results from other trials.

"This study didn't happen over night," said Borenstein, who was not involved in the research. "They followed people for an extended period of time, and it was remarkable that over 50% of people had back pain that extended over a long period."

Borenstein noted that depression can compromise people's ability to cope with pain. Back pain has multiple forms. and at least 60 different causes and, increasingly, rheumatologists are focusing on non-mechanical factors that don't involve physical stress on the skeleton, he pointed out.

"In osteoarthritis and other forms of arthritis, we have come to see that fat in and of itself can be an inflammatory substance," he said. "Adipokines are produced by fat cells in people with excess weight, and these bad actors can have chemical effects that are inflammatory. These may play a role in back pain."

He also highlighted the finding that risk can be modified by regular vigorous exercise. "So we can't just sit back and assume that this pain can't be modified," he said.

The study was funded by the Australian Government Department of Health and Ageing.

Some co-authors disclosed support from the National Health and Medical Research Council and the Arthritis Australia Foundation.

Cicuttini and co-authors disclosed no relevant relationships with industry.