Increased risk of hip fracture among spouses—evidence of a homogamy effect

C. H. Vala, A. Odén, M. Lorentzon, V. Sundh, H. Johansson, M. Karlsson, B. Rosengren, C. Ohlsson, B. Johansson, J. Kanis, D. Mellström

Spouses tend to share habits and therefore have an increased risk of same diseases. We followed all married couples in Sweden, born 1902 to 1942, in hospital records from 1987 to 2002, and found that individuals whose spouse had a hip fracture had an increased risk of hip fracture. The purpose of this study was to determine whether spouses of hip fracture patients have an elevated risk of hip fracture. We performed a retrospective cohort study of all couples married for at least 5 years in Sweden and born between 1902 and 1942 (n = 904,451) and all patients registered with a hip fracture (n = 218,285) in the National Inpatients Register in Sweden from 1987 to 2002. During the period 1987 to 2002 hip fractures occurred among spouses in 4212 married couples. The hazard ratio (HR) for hip fracture in a married woman following hip fracture in the husband was 1.11 (95 % confidence interval 1.07 to 1.16) compared to a woman whose husband did not have hip fracture. The corresponding HR for a married man was 1.20 (1.15 to 1.26) compared to a man whose wife did not have hip fracture. The risk was significantly elevated over the age range 60 to 90 years. The increased risk for hip fracture among spouses remained after adjustments for income, education, geographical latitude and urbanisation. In a common model with spouses and their siblings, the HR for spousal effect were 1.63 (1.01 to 2.64) and for sibling effect 2.18 (1.55 to 3.06) compared to married with spouse and sibling respectively without hip fracture. The novel finding of an increased risk for hip fracture among spouses provides evidence indicating that there is a homogamy effect due to common social and lifestyle factors but could also be due to assortative mating.