There are claims that sound too good to be true. And then there are studies involving 3.4 million people that support 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 which factors promote health or illness in large groups).
This article summarizes what the research — specifically two groundbreaking studies — actually shows. What it does not 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 Scientific Reports — a peer-reviewed journal (reviewed by independent scientists) of the Nature group.
The study used linked Swedish national registries — health registries, population registries, and the Swedish dog ownership registry — 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 influence on cardiovascular diseases and all-cause mortality (the risk of dying for any reason 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 a dog — after adjustment 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 heart attack patients living alone without a dog
• For stroke survivors living alone 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 frequently than people without a dog within a certain 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 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?
Researchers suspect this is due to the higher level of physical activity of hunting dog owners. Hunting dogs like Labrador Retrievers, Golden Retrievers, or Spaniels need a lot of daily exercise — their owners consequently get more exercise. 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 state important limitations. First, the study is observational — it can show that dog ownership and better health are related, 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.
Second, 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 that goes for a walk 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. titled 'The Benefits of Dog Ownership for Mental, Physical, and Social Health' appeared in the Healthy Populations Journal.
This study uses a different methodology than the Uppsala study. It does not analyze its own data but summarizes 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 more physically active, have lower blood pressure, and a lower risk of cardiovascular diseases. This is consistent across several independent studies.
New and remarkable: One study showed that petting a dog measurably reduces cortisol levels (the stress hormone that damages the heart and blood vessels and weakens the immune system when chronically elevated) 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 petting 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 researchers emphasize that it remains unclear whether healthier people are more likely to own dogs or whether the dog improves mental health.
The use of dogs in animal-assisted therapy (the targeted use of animals in therapeutic settings with professional guidance) is particularly well-documented. 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 of current research
A research area that has only recently gained momentum 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 suspected 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 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 give their owners 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 who live 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 probably work together.
Exercise
The most direct and best-documented mechanism. Dogs need to be walked — daily, regularly, in all weathers. Dog owners accumulate significantly more moderate physical activity per week on average than people without a dog. 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 that is released during social interactions and strengthens trust, well-being, and social bonding). 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 contacts and thus reduce the risk of social isolation. This mechanism particularly well explains the increased protective effect in people living alone.
Microbiome diversity
Dogs introduce 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 does not 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 correlation 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 — people cannot be divided into dog owners and non-dog owners by lot — these studies cannot prove causality (cause-and-effect relationship). It remains possible 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 totality of 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 recognition 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 benefits us also benefits them. What harms them also harms us. Healthy environment, healthy animals, healthy people — that is not a metaphor. That is a research paradigm that increasingly shapes global health policy.
The World Small Animal Veterinary Association founded a One Health Committee in 2010 — with the explicit goal 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 — and are thus 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 new but promising
What we cannot say with certainty:
• Whether dogs are causally linked to better health — or whether healthier people are more likely to own dogs
• Whether the effect applies to all people and all types of dog keeping
• What the magnitude of the effect of individual mechanisms (exercise vs. stress reduction vs. microbiome) is
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 global health agenda |
wsava.org |
In conclusion
Science is increasingly providing solid 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 felt it in the 12th century. Uppsala University proved 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. 🐾🧡
