Does having a dog reduce the risk of cardiovascular disease?

Relation

Mubanga M, Byberg L, Nowak C, et al. Dog ownership and the risk of cardiovascular disease and death - a nationwide cohort study.Scientific Rep. 2017;7(1):15821.

Purpose

To examine the association between dog ownership and the risk of cardiovascular disease (CVD) and death.

Draft

This study reports the analysis of two separate cohorts: a registry-based prospective nationwide cohort (n = 3,432,153) and a second smaller cohort, a self-reported group (n = 34,202).

Participant

All Swedish residents aged 40 to 80 years on January 1, 2001 (N = 3,987,937) were eligible for this study. This age group excluded younger people who are at low risk of cardiovascular disease and older people who are unlikely to own a dog. Individuals who had not lived continuously in Sweden since 1987 (n=163,156) and those whose personal identification numbers were unconfirmed (n=5,057) were excluded from the study. Additionally, individuals who had inpatient visits (n = 387,571) for cardiovascular disease or certain cardiovascular procedures were excluded. This still resulted in an extremely large cohort (n = 3,432,153). All Swedish residents are covered by the public health system, and the occurrence of diseases is tracked through medical records.

This Swedish study is by far the largest and most thorough attempt to date to find a connection between dog ownership and health.

A second subgroup cohort was formed from participants in the Screening Across the Lifespan Twin Study (SALT), a substudy of the Swedish Twin Register (STR). SALT, a longitudinal study, began in 1958 and has included most twins born in Sweden since 1886. All SALT participants who responded to telephone interviews between 1998 and 2002 and were between 42 and 80 years of age in 2001 were eligible for study analysis (n = 41,039).

Dog ownership

Sweden requires that all dogs in the country have a unique identifier (tattoo or chip) registered with the agricultural authority. In addition, the Swedish Kennel Club registers all dogs with a certified pedigree. Around 83% of dogs in Sweden are listed in one of these registers. For the purposes of this study, dog ownership was defined as the dog registered in one or both of these registries for either the owner or a partner. Information about dog breeds comes from these registries.

Target parameters

Public registries and medical records provided data on death and cause of death of human participants. Four incidental causes of death were recorded: 1) acute myocardial infarction; 2) heart failure; 3) ischemic stroke; and 4) hemorrhagic stroke.

Key insights

In both single-person and multi-person households, dog ownership was associated with significantly lower all-cause and cardiovascular disease mortality.

The hazard ratios (HRs) for the overall risk of death were 0.67 for single-person households (95% confidence interval [CI]: 0.65-0.69) and 0.89 for multi-person households (95% CI: 0.87-0.91). For death from cardiovascular causes, the HRs were 0.64 for single-person households (95% CI: 0.59–0.70) and 0.85 for multi-person households (95% CI: 0.81–0.90).

In single-person households, dog ownership was inversely associated with cardiovascular outcomes (composite HR: 0.92; 95% CI: 0.89–0.94). Owning hunting dogs was associated with the lowest risk of CVD.

Owning a mixed breed dog was associated with a higher risk of CVD (HR: 1.13; 95% CI: 1.09-1.17). The HR for all-cause mortality was <1 for all breed groups, with pointers associated with the lowest estimate (HR: 0.60; 95% CI: 0.53-0.68) and mixed-breed dogs with estimates closest to 1 (HR: 0.98); 95% CI: 0.94–1.01).

Analysis of data from the twin cohort revealed no significant associations between CVD and dog ownership.

Practice implications

Cardiovascular diseases are now the most common cause of death worldwide. In Europe, (link removed). Interventions that reduce risk by even small percentages will still have a large impact. There is a belief that owning a dog reduces the risk of CVD by providing social and emotional support and increasing the owner's physical activity. Dog ownership, especially among single and older adults, can reduce feelings of social isolation and depression.¹It's easier to make friends when you have a dog,²and, no surprise, dog owners walk more than non-owners. A 2011 meta-analysis of 11 studies confirmed this;³Not only do people walk more after getting a dog,⁴They rain or shine and don't let bad weather stop them from going for a walk.⁵

Previous studies that have attempted to demonstrate the benefits of dog ownership have reported less than consistent results. Some studies have reported that ownership is inversely associated with cardiovascular risk factors such as dyslipidemia, hypertension and diabetes.⁶however, other studies do not.⁷

A Norwegian prospective cohort study published in June 2017 found no difference in all-cause mortality between dog owners and non-owners. Dog owners in this study did not report greater physical activity than non-owners; both groups reported just over 3 hours per week. Owners had virtually the same risk of death as non-owners (HR: 1.00; 95% CI: 0.91-1.09).⁸Note that the number of participants in this Norwegian study was 28,746; This Swedish study included almost 4 million participants, making it 133 times larger.

There were 3 additional studies conducted using data from the National Health and Nutrition Survey (NHANES), all relatively small, each including between 4,000 and 6,000 dog owners; These studies also reported no significant effects of dog ownership on all-cause mortality.^9-11

This Swedish study is by far the largest and most thorough attempt to date to find a link between dog ownership and cardiovascular disease. Both because of its size and the greater accuracy of follow-up through government registries, this study allows for less credence to be given to previous failed attempts to demonstrate benefits of dog ownership. Health registries enabled assessment of both cardiovascular and all-cause mortality. The large size of this Swedish study cohort also enabled the subgroup analysis to reach significance; for example, analyzing data by household type and, interestingly, by dog ​​breed. The different result depending on dog breed is intriguing and may explain previous failures in detecting benefit when dog types were not taken into account. If some types of dogs actually increase risk while others decrease risk, studies analyzing the effects of owning a dog regardless of breed may find no benefit.

Although this paper does not demonstrate causality, it is still hard to ignore the difference in HR between dog types. Based on these results, one might be forced to discourage ownership of dogs that are associated with a higher risk in favor of dogs that are associated with a lower risk of death.

The impact on disease risk appears to vary by dog ​​breed. For example, owning a retriever was associated with a 10% decrease in CVD [adj HR 0.90 (0.87–0.94)] and a 26% decrease in all-cause mortality [0.74 (0.71–0.77)]. On the other hand, owning a mixed-breed dog was associated with a 13% increased risk of cardiovascular disease [1.13 (1.09–1.17)] and only a 2% decrease in all-cause mortality [0.98 (0.94–1.01)]. However, on average, dog ownership was associated with a 23% decrease in cardiovascular mortality [0.77 (0.73–0.80)] and a 20% decrease in all-cause mortality [0.80 (0.79–0.82)].

These tables provide an interesting picture of the data:

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