Oral contraceptives and back pain in women in a Swedish community.

The prevalence of back pain among Swedish women 16-84 years of age has increased from 6.1% in 1975 to 8.1% in 1989; no such increase has been recorded for Swedish men. To determine whether an association exists between back pain and oral contraceptive (OC) use a register study was conducted at the major health center in Tierp Sweden; 65% of the 45000 physician visits made each year by the population of this municipality were to this site. The 503 women prescribed OCs in 1980 (19.08% of women 14-44 years of age in the study area) served as cases; age-matched non-users were controls. Lower back pain was recorded significantly more frequently each year during the 1981-85 follow-up period among OC users than among controls (p < 0.01 in the first year and < 0.05 in the fourth year). Pregnancy was not a confounding factor. However the register did not allow analysis of life-style factors such as heavy physical work smoking or obesity that are also associated with back pain. Moreover bias could have been introduced by the fact that OC users made more health center visits increasing the potential for diagnosis. Additional studies are required to determine whether the OC-back pain association identified in this study is causal.