🐾 Why a dog prolongs your life — what science really knows

There are claims that sound too good to be true. And then there are studies involving 3.4 million people that substantiate these claims.

Dogs make people healthier. This is not romanticism. This is epidemiology (the scientific study of health and disease in populations — it doesn't ask why an individual person gets sick, but what factors promote health or disease in large groups).

This article summarizes what research – specifically two seminal studies – actually shows. What it doesn’t show. And which biological mechanisms could explain the results.

 

Study 1 — The Uppsala Study: 3.4 Million People, 12 Years

What was investigated?

In 2017, an international research team led by Mwenya Mubanga from Uppsala University published a study in Scientific Reports – a peer-reviewed journal from the Nature group.

The study utilized linked Swedish national registers – health registers, population registers, and the Swedish dog ownership register – and observed 3,432,153 individuals aged 40 to 80 over a period of up to 12 years. It is one of the largest epidemiological studies ever conducted on the human-dog relationship.

The central question: Does dog ownership have a measurable impact on cardiovascular diseases and all-cause mortality (the risk of dying from any cause within a certain period)?

 

What was found?

The results are statistically robust and remarkably consistent:

 

•    Dog owners had a 33 percent lower risk of dying from cardiovascular diseases than people without dogs – after adjusting for age, gender, education, place of residence, and other factors

•    The overall mortality risk during the observation period was 24 percent lower for dog owners

•    For people living alone who had suffered a heart attack, the risk of death in the following year was 33 percent lower than for lone heart attack patients without a dog

•    For lone stroke survivors with a dog: 27 percent lower risk of death

•    Owners of hunting dogs — retrievers, spaniels, pointers — showed the strongest protective effect

 

What do these numbers mean specifically?

An important clarification: All people die. 100 percent. What the study shows is not that dog owners are immortal – but that they died less often during a certain observation period than people without dogs. In other words: Dog owners lived longer during these 12 years.

The 24 percent lower overall mortality risk specifically means: If, for example, 10 out of 100 people without a dog died during this period, only about 7 to 8 out of 100 dog owners died. This is a substantial difference – an enormous effect at the population level.

 

Why were hunting dog owners particularly protected?

The researchers suspect that this is due to the higher level of exercise undertaken by hunting dog owners. Hunting dogs such as Labrador Retrievers, Golden Retrievers, or Spaniels require a lot of daily exercise—their owners consequently move more. Regular moderate physical activity is one of the most well-documented protective factors against cardiovascular diseases and premature death.

 

Study Limitations

The authors themselves identify important limitations. First, the study is observational—it can show that dog ownership and better health are correlated, but cannot prove that the dog is the cause. It could be that healthier, more active people are more likely to own dogs—and not vice versa.

Second, information about the type of relationship with the dog is missing – a dog living in a kennel has different effects than a dog walked daily. Third, only cardiovascular diseases and all-cause mortality were recorded – other health aspects were not investigated.

 

Study 2 — The Benefits of Dog Ownership (2024): Body, Mind, and Microbiome

 

What was investigated?

In 2024, a comprehensive review—a systematic summary of the current state of research—by Matijczak et al. was published in the Healthy Populations Journal under the title 'The Benefits of Dog Ownership for Mental, Physical, and Social Health.'

This study uses a different methodology than the Uppsala study. It does not analyze its own data but rather synthesizes the findings of dozens of existing studies – thus providing a broad overview of the entire research field. The focus: How does dog ownership affect physical health, mental health, and social health?

 

Physical Health — What the Research Shows

The review confirms the results of the Uppsala study: Dog owners are more physically active, have lower blood pressure, and a lower risk of cardiovascular disease. This is consistent across several independent studies.

New and remarkable: One study showed that stroking a dog measurably reduces cortisol levels (the stress hormone which, when chronically elevated, damages the heart and blood vessels and weakens the immune system) after just a few minutes, while simultaneously increasing serotonin (a neurotransmitter – a chemical messenger in the brain – that regulates mood, sleep, and appetite) and dopamine (another neurotransmitter associated with motivation, reward, and well-being). This effect is dose-dependent – more interaction shows more effect – and occurs regardless of whether the person stroking the dog knows it or not.

 

Mental Health — Depression, Anxiety, Trauma

The authors summarize numerous studies on the psychological effects of dog ownership. The results consistently show a reduction in symptoms of depression and anxiety disorders in dog owners – though the researchers emphasize that it remains unclear whether healthier people are more likely to own dogs, or whether the dog improves mental health.

Particularly well-documented is the use of dogs in animal-assisted therapy (the targeted use of animals in therapeutic settings under professional guidance). Randomized controlled trials – the methodologically strongest form of studies – show positive effects in post-traumatic stress disorder (PTSD), where traumatic experiences are relived repeatedly and interfere with daily life, as well as in anxiety disorders and obsessive-compulsive disorders.

The authors point out that a dog is not a substitute for professional psychological or psychiatric treatment – but can be a valuable complementary factor.

 

The Microbiome — the Most Surprising Finding in Current Research

A research area that has only gained momentum in recent years is the connection between dog ownership and the human microbiome (the totality of all microorganisms – bacteria, viruses, fungi – that live on and in the human body and influence digestion, the immune system, and even mental health).

A study published in 2025 in the journal iScience examined adolescents who grew up with dogs compared to adolescents without dogs. The result: The gut microbiome differed significantly – and the adolescents with dogs showed fewer psychological problems.

The presumed mechanism: Dogs change the microbiome in the household. They bring new bacterial strains daily – from outside, from nature, from other animals. This diversity is transferred to the residents of the household. A diverse microbiome has been associated with better immune function, lower inflammation levels, and better mental health in numerous studies.

This finding is particularly relevant for children: growing up with a dog early on seems to train the developing immune system and could have long-term protective effects. Research on this is still in its early stages – but the initial results are remarkable.

 

Social Health — Loneliness, Community, Social Inclusion

Loneliness has become a serious health problem in Western societies. The World Health Organization (WHO) has called loneliness a global health crisis. Chronic loneliness is a risk factor for premature death comparable to smoking 15 cigarettes daily.

The review shows that dogs act as social catalysts (factors that accelerate or facilitate social processes). They provide structure and rhythm to their owners – daily dog walks force them to leave the house and create encounters. Dog people talk to each other – on the street, in the park, at the vet. These social contacts are often fleeting but regular – and regular social interaction demonstrably protects against loneliness.

This effect is particularly pronounced in older people living alone. One study showed that older dog owners living alone had significantly higher levels of social inclusion and perceived well-being than older people living alone without a dog.

 

What biological mechanisms explain these effects?

Research proposes several mechanisms – they are not mutually exclusive and likely interact.

 

Exercise

The most direct and well-documented mechanism. Dogs need to be walked – daily, regularly, in all weather. Dog owners accumulate significantly more moderate physical activity per week on average than people without dogs. Regular moderate exercise lowers blood pressure, improves blood lipid levels, reduces inflammatory markers, and strengthens the cardiovascular system. This is one of the best-documented mechanisms in all of medicine.

 

Stress reduction and hormonal effects

Interaction with dogs – petting, playing, simply being near them – lowers cortisol levels and increases oxytocin (the so-called bonding hormone released during social interactions, which strengthens trust, well-being, and social connection). Chronically elevated cortisol damages the heart, blood vessels, and immune system in the long term. The reduction of cortisol through interaction with dogs is a plausible mechanism for the cardioprotective effect.

 

Social inclusion

Social isolation is an independent risk factor for cardiovascular diseases and premature death – biologically plausible through increased cortisol secretion, chronic inflammation, and behavioral changes. Dogs promote social contact and thus reduce the risk of social isolation. This mechanism explains the increased protective effect in people living alone particularly well.

 

Microbiome diversity

Dogs bring new microorganisms into the household daily. This increased microbial diversity in the living environment can train the immune system and diversify the residents' microbiome. A diverse microbiome has been associated with reduced inflammation levels, better immune function, and better mental health in numerous studies. This mechanism is still less well understood than the others – but increasingly well documented.

 

What the research doesn't say — scientific honesty

Not all studies on dog ownership and health show positive effects. Some meta-analyses (systematic summaries of many studies) find no significant association between dog ownership and all-cause mortality when strict methodological criteria are applied.

The methodological challenge is considerable: Since dog ownership cannot be assigned randomly – one cannot randomly assign people to dog owners and non-dog owners – these studies cannot prove causality (cause-and-effect relationship). The possibility remains that healthier, more active, more social people are more likely to own dogs – and not vice versa.

What does this mean for interpretation? A dog is not a medication. Not a substitute for exercise, a healthy diet, medical treatment, or psychological support. The sum of the evidence – especially the Uppsala study with its unique data basis and methodological strength – suggests that the human-dog relationship has measurable positive effects on health and life expectancy. But these effects are not guaranteed and not the same for all people.

 

One Health — one health for humans, animals, and the environment

The World Health Organization, the World Organisation for Animal Health, and the Food and Agriculture Organization of the United Nations are increasingly working under the concept of One Health — the scientifically well-founded understanding that human health, animal health, and environmental health are inextricably linked.

Within this framework, dogs are not just companions – they are active factors in our health. And we are active factors in their health. The relationship is bidirectional: what is good for us is also good for them. What harms them also harms us. A healthy environment, healthy animals, healthy people – this is not a metaphor. This is a research paradigm that increasingly shapes health policy worldwide.

The World Small Animal Veterinary Association founded a One Health Committee in 2010 – with the explicit aim of embedding the importance of companion animals for human health in the global health agenda. Dogs spontaneously develop the same diseases as humans – cancer, heart disease, allergies, autoimmune diseases – making them unique research models for human medicine.

 

Summary – what we know and what we don't know

 

What we can say with high certainty:

•    Dog owners are more physically active – this is well-documented and causally plausible

•    Interaction with dogs lowers cortisol and increases oxytocin, serotonin, and dopamine – measurable, reproducible

•    Dogs act as social catalysts and reduce social isolation

•    The Uppsala study, with 3.4 million people, shows a robust statistical link between dog ownership and lower cardiovascular risk

•    Dog ownership is associated with a better microbiome – research on this is nascent but promising

 

What we cannot say with certainty:

•    Whether dogs are a causal factor for better health – or whether healthier people are more likely to own dogs

•    Whether the effect applies to all people and all forms of ownership

•    The magnitude of the effect of individual mechanisms (exercise vs. stress reduction vs. microbiome)

 

References

This article is for informational purposes and does not replace medical advice.

 

No.	Author/Year	Topic	Source
1	Mubanga et al. (2017)	Dog ownership and the risk of cardiovascular disease and death — 3.4 million people, 12 years, Uppsala University	Scientific Reports. DOI: 10.1038/s41598-017-16118-6
2	Matijczak et al. (2024)	The Benefits of Dog Ownership for Mental, Physical, and Social Health — systematic review	Healthy Populations Journal
3	iScience (2025)	Dog ownership during adolescence alters the gut microbiota and improves mental health	DOI: 10.1016/j.isci.2025.02209
4	Levine et al. (2013)	Pet Ownership and Cardiovascular Risk — Statement by the American Heart Association	Circulation. DOI: 10.1161/CIR.0b013e31829201e1
5	WHO / FAO / WOAH (2022)	One Health Joint Plan of Action — framework for integrated human-animal-environment health	who.int/one-health
6	World Small Animal Veterinary Association (2010)	One Health Committee — Importance of companion animals for global health agenda	wsava.org

 

In conclusion

Science is increasingly providing robust evidence for what many dog people intuitively know: The relationship between humans and dogs is not a sentimental matter. It has measurable biological effects – on the heart, brain, microbiome, and social life.

Hildegard von Bingen sensed it in the 12th century. Uppsala University confirmed it with 3.4 million data points. And research continues – because the more we understand how this bond works, the better we can shape it. For us. And for them. 🐾🧡

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