4th January 2020, Dr Chee L Khoo
Anecdotal evidence suggests that having a pet reduces cardiovascular mortality. Does it? You can imagine that trying to conduct a randomised control trial can be difficult. One has to consider the pre-existing risks profile of the pet owner, physical activity pre and post pet ownership, marital status of the owner and whether pet ownership benefits men or women more. Well, the evidence is rather conflicting though. It is still worthwhile examining the evidence because if the benefits are there, we should be recommending pet ownership to many of our patients.
The potential health benefits of dog ownership have been described for several decades, and thought to result from dog-human interactions, companionship and interaction, especially among older adults [1-4]. It is presumed that this social support leads to reduced loneliness and improved cardiovascular health, possibly partly mediated through reductions in blood pressure (5) or via stress reduction [1,6], possibly through oxytocin effects [7].
In the primarily rural based, Norwegian Nord-Trøndelag HUNT Study, 53,418 participants were followed up on average for 18.5 years. Living in a household with a dog was not associated with a reduction in mortality. In this population, dog owners and non-dog owners did not differ in their physical activity levels. Dog ownership may not automatically lead to increase in physical activity.
Not only do the Swedes keep a complete medical database of its population, since January 2001, every dog in Sweden has a unique identifier complete with a certified pedigree. How good is that? In a nationwide cohort study, among ~3.5 million people, 13.1% were identified as dog owners during a 12 year study period (9). Dog ownership was associated with reduced risk of acute myocardial infarction, ischemic stroke, heart failure, and composite CVD. Interestingly but not unexpectedly, they found ownership of a dog from breeds originally bred for hunting (including terriers, retrievers, scent hounds and related dogs) was associated with a lower risk of CVD. Perhaps, owners of these breeds were more physically active.
Yet, when investigators looked at six cohort of the Health Survey for England (between 1995-2004), they found no evidence for an association between living in a household with a dog and all-cause or cardiovascular disease mortality. Of note though, while dog owners reported more vigorous physical activity than non-dog owners, dog owners were also more likely to smoke (10).
Like the Swedes, the Danish also have unique identifiers for both humans and animals. In a population based case control study, 275,184 people were studied over (11). 8% were dog owners, Dog owners were younger (mean 68 years) than non-dog onwers (mean 77 years). Dog ownership was associated with an overall 8% reduction in mortality. The reduction was more stark in people without a spouse (14% reduction).
Perhaps, we are not seeing benefits of dog ownership in the general population. What about patients who are at high risk of cardiovascular events? What about patients who already have an acute cardiovascular event? Mubunga et al used the Swedish National Patient Registry to identify individuals who had just suffered either an acute AMI or ischaemic stroke and looked at all cause mortality and recurrent admissions for the same cause. Dog owners had a lower risk of death after AMI (HR of 0.67 for those living alone and HR 0.85 for those living with a partner or child). For ischaemic strokes the HR were dog owners were 0.73 and 0.88 respectively for those without spouse and for those with a spouse or child. There was also a reduction in hospitalisation for recurrent myocardial infarction (HR 0.93) amongst dog owners.
When Kramer et al search for all studies between 1950 and May 2019, they yielded 10 studies. They performed a meta-analysis and found that dog ownership was associated with a 24% risk reduction for all-cause mortality as compared to non-ownership.
Conclusion
Although the evidence of benefits of dog ownership is conflicting, it would seem plausible that dog ownership confers cardiovascular benefit especially if dog owner ship results in increased physical activity. The evidence of benefits is stronger in patients with establish cardiovascular diseases.
Dog ownership can also lead to some regimentation of routine forcing owners to wake up at set time (try sleeping in when you have a dog!). There may be other calming benefits with dog ownership resulting in lower blood pressure, heart rates and possibly lipid profiles. Improvements in mental health by having a companion may lead to lower rates of depression, decreased lonliness and increased self-esteem. This may explained the better outcomes among dog owners without a spouse or child.
Adopting a dog is a major undertaking though. . It is a much larger undertaking than embarking on a new medical therapy. Adding a 4-legged member to the family involves long-term commitment, often substantial lifestyle changes and financial costs.
References:
- Serpell J (1991) Beneficial effects of pet ownership on some aspects of human health and behaviour. Journal of the Royal Society of Medicine 84: 717–720. pmid:1774745
- Cherniack EP, Cherniack AR (2014) The benefit of pets and animal-assisted therapy to the health of older individuals. Current Gerontology and Geriatrics Research 2014.
- Toohey AM, McCormack GR, Doyle-Baker PK, Adams CL, Rock MJ (2013) Dog-walking and sense of community in neighborhoods: Implications for promoting regular physical activity in adults 50 years and older. Health and Place 22: 75–81.
- Cutt H, Giles-Corti B, Knuiman M, Burke V (2007 Mar) Dog ownership, health and physical activity: A critical review of the literature. Health Place 13: 261–272.
- Headey B (1999) Health benefits and health cost savings due to pets: preliminary estimates from an Australian national survey. Social Indicators Research 47: 233–243.
- Dembicki D, Anderson J (1996) Pet ownership may be a factor in improved health of the elderly. Journal of Nutrition for the Elderly 15: 15–31.
- Matchock RL (2015) Pet ownership and physical health. Current Opinion in Psychiatry 28: 386–392. pmid:26164613
- Torske MO, Krokstad S, Stamatakis E, Bauman A (2017) Dog ownership and all-cause mortality in a population cohort in Norway: The HUNT study. PLoS ONE 12(6): e0179832. https://doi.org/10.1371/journal.pone.0179832
- Mubanga, M., Byberg, L., Nowak, C. et al. Dog ownership and the risk of cardiovascular disease and death – a nationwide cohort study. Sci Rep 7, 15821 (2017) doi:10.1038/s41598-017-16118-6
- Ding D, Bauman AE, Sherrington C, McGreevy PD, Edwards KM, Stamatakis E. Dog Ownership and Mortality in England: A Pooled Analysis of Six Population-based Cohorts. Am J Prev Med. 2018;54(2):289–293. doi:10.1016/j.amepre.2017.09.012
- Ivalu Katajavaara Sørensen, Pernille Envold Bidstrup, Naja Hulvej Rod, Tjorben Rühling, Christoffer Johansen, Is dog ownership associated with mortality? A nationwide registry study, European Journal of Public Health, Volume 28, Issue 6, December 2018, Pages 1169–1171
- Kramer, Caroline K. MD, PhD; Mehmood, Sadia BSc; Suen, Renee S. Dog Ownership and Survival: A Systematic Review and Meta-Analysis. Circulation: Cardiovascular Quality and Outcomes. Volume 12(10), October 2019