Do pets add years?

Sweden’s national registers were linked for 3,432,153 adults aged 40–80 with no cardiovascular disease at baseline, followed for about 12 years. Among people living alone, dog owners had 33% lower all-cause mortality (hazard ratio 0.67, 95% CI 0.61–0.74) and 36% lower cardiovascular mortality (0.64, 0.55–0.74) than non-owners living alone; among people living with others the effect was smaller, 11% and 15% (0.89 and 0.85). Hunting breeds, retrievers (0.90), scent hounds (0.93) and terriers (0.95), carried the strongest associations, consistent with an activity pathway [2]. A meta-analysis of 10 cohorts, 3,837,005 people and 530,515 deaths found dog owners had 24% lower all-cause mortality (relative risk 0.76, 0.67–0.86), 31% lower cardiovascular mortality, and 65% lower mortality after a heart attack or stroke; its authors note the pooled studies were not adjusted for confounders [3]. Adjusted cohorts since then disagree: 23% lower odds of death for Australian dog owners over 4 years (odds ratio 0.77, 0.59–0.99) [5], and no difference in 23,274 Europeans over 50 (hazard ratio 1.01, 0.94–1.10) [4]. Your Lifespan chart converts the pooled 0.76 with the same years formula every habit uses: +3.2 years*, refined by the living-alone split from the Swedish registry.

The most-cited cat study followed 4,435 people from the Second National Health and Nutrition Examination Survey for 20 years. People who had ever owned a cat had 37% lower risk of fatal heart attack than never-owners, after adjusting for age, sex, race, blood pressure, smoking, diabetes, cholesterol and body-mass index, but the association held only for past ownership, not current, and the sample came from a subgroup assembled to study allergies [1]. A later NHANES analysis of 3,964 adults over 50 found lower stroke death in women who owned cats (hazard ratio 0.22), with no such link in men [10]. Cohorts that counted every death found no clear difference for cat owners: odds ratio 0.77 (0.56–1.05) in Australia [5] and hazard ratio 1.03 (0.95–1.12) in Europe [4]. Your Lifespan chart bridges the heart-attack figure through the share of deaths that are cardiovascular, the same outcome-fraction bridge the hot-tub figure uses: +1.1 years*, tier Very low.

Two cohorts split out fish owners. In 23,274 Europeans over 50, fully adjusted, fish owners died at exactly the same rate as people with no pet (hazard ratio 1.00, 0.84–1.19) [4]; in 15,735 Australians the odds leaned lower but not significantly (odds ratio 0.68, 0.30–1.54) [5]. A systematic review of 19 studies found watching fish in aquariums lowered heart rate and anxiety and lifted mood in the short term, with every study at high or unclear risk of bias and none measuring lifespan [6]. Your Lifespan chart converts the European hazard ratio to +0 years, starred in the table above: a measured null, not a gap.

In the same 23,274 Europeans, bird owners died slightly more often than people with no pet, not significantly (hazard ratio 1.05, 0.93–1.19), and women bird owners significantly more often (1.23, 1.04–1.44), mostly from causes other than cancer and heart disease [4]. The Australian cohort leaned the other way, also not significantly (odds ratio 0.69, 0.40–1.22) [5]. Because the range includes no difference, your Lifespan chart reads it as +0 years, starred in the table above with the working (the point estimate alone would be −0.6 years), the same rule the Movement chart uses for a published null.

No study has followed owners of horses, rabbits, guinea pigs, reptiles or other animals to see how long they live. The closest is the Australian cohort’s mixed “other pets” group, which showed no clear link either way (odds ratio 0.80, 0.33–1.92) [5]. With nothing measured to convert or bridge from, these answers show no number on your Lifespan chart, not a zero, and they count toward no total or score: picking one reads exactly as if you had skipped the question.

In a UK community sample of 191 dog-owning and 455 non-dog-owning adults across 385 households, dog owners had over 14 times the odds of any recreational walking (odds ratio 14.35, 95% CI 5.77–35.79) and over 4 times the odds of meeting the 150-minutes-a-week activity guideline (4.10, 2.05–8.19). Every other type of physical activity measured, sport, gym, cycling, showed no difference between owners and non-owners, isolating the effect to dog walking [11]. This lines up with the Swedish registry finding that hunting and scent-hound breeds, which need the most exercise, carried the strongest mortality association.

A meta-analytic review across many cohorts found social isolation, loneliness and living alone each independently tracked with roughly 26% to 32% higher mortality (adjusted odds ratios 1.29, 1.26 and 1.32) [12]. This is not a pet study: it is the general evidence that loneliness itself carries real mortality risk, the plausible reason the Swedish registry found the dog effect roughly three times larger in people living alone.

Every study above is observational, and every one of their authors flags the same limitation: people who are healthier, wealthier, more mobile and better housed are more likely to get and keep a pet, which would produce exactly this pattern even if the animal changed nothing, the “healthy pet owner effect”. A registry of 3.4 million people rules out chance, but not this kind of selection; only a randomised trial could, and nobody randomly assigns adults a dog for 12 years. The adjusted cohorts make the point from the other side: once they account for health and wealth, most of the pet differences shrink toward none.

Keep the two apart. Houseplants: the claim that they clean indoor air fails at room scale. A review of 196 chamber experiments put a typical potted plant’s clean-air delivery at 0.023 cubic metres an hour, so you would need 10 to 1,000 plants per square metre of floor to match what ordinary ventilation already does [9]. What houseplants measurably do is calm: in a crossover trial of 24 young men, a short session repotting a plant lowered sympathetic nervous activity and diastolic blood pressure compared with computer work [8]. That is a one-session effect, and no study links keeping houseplants to how long you live, so houseplants have no longevity number yet. Gardening outdoors is different, because it is exercise. In a randomised trial of 291 adults, a season of community gardening added 5.8 minutes a day of moderate-to-vigorous activity and 1.4 g a day of fibre compared with waiting-list controls, and cut stress and anxiety [7]. Run through the dose-response of 416,175 Taiwanese adults, where every extra 15 minutes of daily activity cut all-cause mortality by 4% [13], that is about +0.2 years*. Cohorts point higher: US adults who gardened had 24% lower mortality over 16.8 years (hazard ratio 0.76, 0.68–0.85) [14], and a generally active daily life, lawn and hedge work included, tracked with 30% lower mortality in 60-year-old Swedes whether or not they exercised [15]. But gardeners are healthier to begin with, so the trial’s measured minutes are the number used here. A meta-analysis of 22 studies found gardening improved measures from depression and anxiety to body-mass index and life satisfaction [16]. Next to pets: gardening sits well below a dog and below a cat, and houseplants, like a horse or a reptile, have nothing measured to put a number on.

Pets and brain health is a separate body of evidence with its own factor on the Cognitive Fitness chart: a brain-scan study and three longer cohorts covering dogs, cats, fish and birds for cognitive decline, not mortality (McDonough et al. [17], and the studies it cites). A pet on the bed has its own sleep-quality factor, and living with a dog its own Movement factor. Each of those takes the same tick-every-one pet answer, and gives the kinds of pet with nothing measured no number.