Logo: to the web site of Uppsala University

Dogs may be beneficial in reducing cardiovascular risk in their owners by providing social support and motivation for physical activity. We aimed to investigate the association of dog ownership with incident cardiovascular disease (CVD) and death in a register-based prospective nation-wide cohort (n = 3,432,153) with up to 12 years of follow-up. Self-reported health and lifestyle habits were available for 34,202 participants in the Swedish Twin Register. Time-to-event analyses with time-updated covariates were used to calculate hazard ratios (HR) with 95% confidence intervals (CI). In single- and multiple-person households, dog ownership (13.1%) was associated with lower risk of death, HR 0.67 (95% CI, 0.65-0.69) and 0.89 (0.87-0.91), respectively; and CVD death, HR 0.64 (0.59-0.70), and 0.85 (0.81-0.90), respectively. In single-person households, dog ownership was inversely associated with cardiovascular outcomes (HR composite CVD 0.92, 95% CI, 0.89-0.94). Ownership of hunting breed dogs was associated with lowest risk of CVD. Further analysis in the Twin Register could not replicate the reduced risk of CVD or death but also gave no indication of confounding by disability, comorbidities or lifestyle factors. In conclusion, dog ownership appears to be associated with lower risk of CVD in single-person households and lower mortality in the general population.

Objective To study the association between dog ownership and cardiovascular risk factors.

Design A nationwide register–based cohort study and a cross-sectional study in a subset.

Setting A cohort of 2 026 865 participants was identified from the Register of the Total Population and linked to national registers for information on dog ownership, prescribed medication, hospital admissions, education level, income and country of birth. Participants were followed from 1 October, 2006, to the end of the study on 31 December, 2012, assessing medication for a cardiovascular risk factor, emigration and death. Cross-sectional associations were further assessed in 10 110 individuals from the TwinGene study with additional adjustment for professional level, employment status, Charlson comorbidity index, disability and tobacco use.

Participants All Swedish residents aged 45–80 years on 1 October, 2006.

Main outcome measures Initiation of medication for hypertension, dyslipidaemia and diabetes mellitus.

Results After adjustment for confounders, the results indicated slightly higher likelihood of initiating antihypertensive (HR, 1.02; 95% CI, 1.01 to 1.03) and lipid-lowering treatment (HR, 1.02; 95% CI, 1.01 to 1.04) in dog owners than in non-owners, particularly among those aged 45–60 years and in those owning mixed breed or companion/toy breed dogs. No association of dog ownership with initiation of treatment for diabetes was found in the overall analysis (HR, 0.98; 95% CI, 0.95 to 1.01). Sensitivity analyses in the TwinGene cohort indicated confounding of the association between dog ownership and prevalent treatment for hypertension, dyslipidaemia and diabetes mellitus, respectively, from factors not available in the national cohort, such as employment status and non cardiovascularchronic disease status.

Conclusions In this large cohort study, dog ownership was associated with a minimally higher risk of initiation of treatment for hypertension and dyslipidaemia implying that the previously reported lower risk of cardiovascular mortality among dog owners in this cohort is not explained by reduced hypertension and dyslipidaemia. These observations may suffer from residual confounding despite access to multiple important covariates, and future studies may add valuable information.