🐾 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 those claims.

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

This article summarizes what the research — specifically two pioneering studies — actually shows. What it doesn't show. And what 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 the journal Scientific Reports — a peer-reviewed journal from the Nature group.

The study used linked Swedish national registries — health registries, population registries, and the Swedish Dog Ownership Register — and observed 3,432,153 people 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 overall 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, sex, education, place of residence, and other factors.

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

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

•    Among single 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 figures mean exactly?

An important clarification: All people die. 100 percent. What the study shows is not that dog owners are immortal — but that they died less frequently than people without dogs during a specific observation period. 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 dogs 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 among hunting dog owners. Hunting dogs like Labrador Retrievers, Golden Retrievers, or Spaniels need a lot of daily exercise — their owners consequently exercise more. Regular moderate physical activity is one of the best-documented protective factors against cardiovascular diseases and premature death.

 

Limitations of the study

The authors themselves highlight important limitations. Firstly, the study is observational — it can show that dog ownership and better health are correlated, but it 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.

Secondly, there is a lack of information about the nature of the relationship with the dog — a dog living in a kennel has different effects than a dog walked daily. Thirdly, only cardiovascular diseases and overall 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. titled 'The Benefits of Dog Ownership for Mental, Physical, and Social Health' was published in the Healthy Populations Journal.

This study uses a different methodology than the Uppsala study. It does not analyze its own data but rather synthesizes the results of dozens of existing studies — thereby 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 physically more active, have lower blood pressure, and a reduced risk of cardiovascular diseases. This is consistent across several independent studies.

New and noteworthy: One study showed that stroking a dog measurably lowers cortisol levels (the stress hormone that, 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 dog is known to the person stroking 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 — although 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 repeatedly relived and impair 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 of 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 the journal iScience in 2025 investigated 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 is 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 as a risk factor for premature death is comparable to smoking 15 cigarettes daily.

The review shows that dogs act as social catalysts (factors that accelerate or facilitate social processes). They provide their owners with structure and rhythm — daily 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 single dog owners had significantly higher levels of social inclusion and perceived well-being than older single people without dogs.

 

What biological mechanisms explain these effects?

Research suggests several mechanisms — they are not mutually exclusive and likely work together.

 

Exercise

The most direct and best-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 — stroking, playing, simply being near them — lowers cortisol levels and increases oxytocin (the so-called bonding hormone that is released during social interactions and 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 disease and premature death — biologically plausible through increased cortisol secretion, chronic inflammation, and behavioral changes. Dogs promote social contacts and thus reduce the risk of social isolation. This mechanism particularly well explains the enhanced protective effect in people living alone.

 

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 is 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 overall mortality when strict methodological criteria are applied.

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

What does this mean for the interpretation? A dog is not a medicine. Not a substitute for exercise, healthy eating, medical treatment, or psychological support. The sum of the evidence — especially the Uppsala study with its unique database 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 everyone.

 

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 realization 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. Healthy environment, healthy animals, healthy people — this is not a metaphor. This is a research paradigm that is increasingly shaping health policy worldwide.

In 2010, the World Small Animal Veterinary Association founded a One Health Committee with the explicit goal of establishing 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, involving 3.4 million people, shows a robust statistical correlation 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 causally linked to better health – or if healthier people are more likely to own dogs.

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

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

 

References

This article is for informational purposes only 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 of 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 the 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 has confirmed it with 3.4 million data points. And research continues – because the more we understand how this connection works, the better we can shape it. For us. And for them. 🐾🧡