Back pain and obesity in the 1958 British birth cohort. cause or effect?

An association between obesity and back pain has been observed, but the underlying causal direction is uncertain. We examined the temporal sequence among back pain, BMI, and weight gain using data from the 1958 British birth cohort followed to age 33 (4395 men and 4468 women). Heights and weights were measured at ages 7 and 33, and self-reported at age 23. Back pain was classified as: chronic, incident, early onset but recovered, and never. Those with chronic pain gained more weight between ages 23 and 33 than those with no pain, significantly for women (7.39 kg vs. 6.29 kg). Women who were obese at age 23 years had an elevated risk of subsequent back pain onset (32-33 years) (adjusted OR = 1.78). No significant relationships were found for men. The risk of pain onset among women was evident in relation to BMI at baseline (age 23) and cannot therefore be explained by an effect of back pain on adiposity.