Pet ownership

The largest single study linked Swedish national registers for 3,432,153 adults with up to 12 years of follow-up; 13.1% owned a dog. Among people living alone, dog ownership was associated with a hazard ratio (the risk in one group relative to another; 0.67 means 33% lower) for death of 0.67 (95% confidence interval, the range within which the true value probably lies, 0.65 to 0.69) and for cardiovascular death of 0.64. Among people living with others the figures were 0.89 and 0.85. Owners of hunting breeds had the lowest risk of cardiovascular disease. In a subgroup of 34,202 participants in the Swedish Twin Register with information on health and lifestyle, the lower risk could not be replicated, although there was no sign of confounding by disability, other illnesses or lifestyle [4].

The 2019 meta-analysis pooled 10 studies with 530,515 deaths over a mean follow-up of 10.1 years. Dog ownership was associated with a relative risk (the risk in one group divided by the risk in another) of 0.76 for all-cause mortality (0.67 to 0.86) and 0.69 for cardiovascular mortality. In people who had already had a coronary event, living with a dog was associated with a relative risk of death of 0.35 (0.17 to 0.69). The authors noted that the analyses were not adjusted for confounders (other factors that could explain the association) [1].

Later studies that adjusted for such factors differ. In the Australian Household, Income and Labour Dynamics study, dog owners had an odds ratio for death of 0.77 (0.59 to 0.99) compared with people without pets, after propensity score matching on socio-demographic, physical, psychological and social factors [2]. In the Survey of Health, Ageing and Retirement in Europe, fully adjusted models showed no significant association for dogs or any other pet [3]. The links between dog ownership and cardiovascular disease are the most consistent part of this evidence.

The main evidence for cats comes from a US national survey of 4,435 adults followed for 20 years. After adjustment for age, sex, ethnicity, blood pressure, smoking, diabetes, cholesterol and body mass index, people who had owned a cat in the past had a relative risk of 0.63 (0.44 to 0.88) for death from heart attack and 0.74 (0.55 to 1.0) for death from all cardiovascular diseases, compared with people who had never had a cat [6]. A later analysis of 3,964 US adults aged 50 and over found that women who owned cats had lower risk of death from stroke (hazard ratio 0.22, 0.07 to 0.68), with no similar association in men [7]. Studies of all-cause mortality found no clear association for cat owners [2, 3].

In the Australian study, ownership of cats, birds, fish and other animals showed no clear association with mortality, even though these owners had socio-demographic characteristics similar to dog owners [2]. In the European study, bird ownership was associated with higher mortality in women (hazard ratio 1.23, 1.04 to 1.44), especially women living alone (1.38), and with higher mortality from causes other than cancer and cardiovascular disease (1.40) [3]. The reason for this finding is not known.

Fish have been studied mainly for short-term effects. A systematic review of 19 studies found tentative evidence that keeping home aquariums is associated with relaxation and mixed evidence on anxiety and physiological stress, with preliminary support for effects on mood; every study had methodological problems and a high or unclear risk of bias [8]. Mortality studies report dogs, cats, birds and fish separately and group other animals together, so there is little evidence on horses, rabbits, reptiles or other species [2].

Walking a dog is the most direct proposed pathway. In a survey of 191 dog-owning adults and 455 adults without dogs in 385 households in West Cheshire, England, dog owners were far more likely to walk for recreation (odds ratio 14.35, 5.77 to 35.79) and had 4.10 times the odds (2.05 to 8.19) of meeting the guideline of 150 minutes of physical activity a week. Other types of physical activity did not differ between owners and non-owners, so the extra activity came from walking and did not replace other exercise [5].

In the Australian mortality study, physical activity partly explained the association between dog ownership and lower mortality [2]. The Swedish finding that owners of hunting breeds had the lowest cardiovascular risk is consistent with an activity pathway [4]. The health effects of daily walking are described under walking and daily steps.

The Swedish registry found a larger association between dog ownership and survival in people living alone (33% lower mortality) than in people living with others (11% lower) [4]. Living alone itself is associated with 32% higher mortality, and social isolation and loneliness with 29% and 26% higher mortality, in pooled studies [9]. A dog may provide company, routine and contact with other people, although these pathways have not been measured directly in the mortality studies. The wider evidence on relationships and health is described under social connection.

Companionship is also proposed as the reason for associations with cats. The authors of the US study of adults aged 50 and over suggested that the lower cardiovascular mortality they observed might reflect the stress-relieving effects of animal companionship or the personality of owners rather than physical activity [7]. The biology of stress is described under stress and anxiety.

Pet ownership has also been examined in relation to thinking and memory. In a cross-sectional study (measured at one time point) of 95 adults aged 20 to 74 in Alabama, the 56 pet owners had higher cognitive scores and larger brain structures than the 39 non-owners, with the largest differences in dog owners; the authors estimated that pet ownership was associated with a brain age up to 15 years younger [10]. The study was small and cannot show whether pets affect the brain or whether healthier people are more likely to own pets.

Full deep dive: Pet ownership and lifespan.

All evidence on pet ownership and mortality is observational. People who are healthier, wealthier, more mobile and better housed are more likely to acquire and keep a pet, and serious illness can lead people to give up a pet, so owners may live longer for reasons unrelated to the animal. The pooled estimate for dogs was not adjusted for such differences [1], and adjusted studies found smaller associations or none [2, 3].

Most studies measured ownership once and did not record how much time owners spent with their animals or how often they walked a dog. The Swedish association could not be replicated in a subgroup with detailed health information [4], and the main cat study was based on past rather than current ownership [6]. No randomised trial has assigned people to own a pet and measured survival.