Socio-demographic factors, reproductive history and risk of osteoarthritis in a cohort of 4.6 million Danish women and men

SummaryObjectiveStudies addressing possible socio-demographic and reproductive factors in the aetiology of osteoarthritis (OA) are few. We studied possible influences of educational level, household income, marital status and parenting patterns on OA risk overall and at anatomical sites.MethodWe linked national register data about socio-demographic variables, reproductive histories and OA hospital contacts to a cohort of 4.6 million Danes. Ratios of first OA hospitalisation rates (RRs) were calculated using Poisson regression.ResultsOverall, 100,437 women and 92,020 men had a first OA hospital contact during 91.5 million person-years between 1982 and 2008. Short education, low income and married status were significantly associated with increased OA risk, and persons with children were at higher risk of OAoverall (RR = 1.10 in women; RR = 1.22 in men), OAknee (RRs 1.14; 1.28), OAback (RRs 1.18; 1.33), and OAhand (RRs 1.21; 1.43), but not of OAhip (RRs 0.96; 1.00) than persons without children. The RR of OAoverall increased by a factor of 1.05 in women and 1.04 in men per additional child, most notably for OAknee in women (1.10 per child).ConclusionRisk of OA hospitalisation was highest among married persons and persons with short education or low income. The similar or even stronger associations with reproductive factors in men than women suggest that unmeasured lifestyle factors rather than biological factors associated with pregnancy might explain the higher OA risk in persons with children. However, the particularly strong association between parity and risk of OAknee in women is compatible with a role of pregnancy-associated factors.