Keeping a companion animal bundles movement, routine, touch and social exchange. Large population studies show owners, dog owners especially, declining more slowly on memory and word-finding tests, the gap largest among people living alone. No one has assigned animals at random, so healthier people simply keeping more pets is not ruled out. Costs: broken bones, infection, asthma, disturbed sleep, grief. (Full Review)

Protocol

Core regimen

30 min daily dog walking

Temperament-assessed animal matched to household mobility; fixed care routine

Split rather than single exposure

2 bouts of 15–20 min

Morning and late afternoon; a single weekend walk does not substitute

Best time of day

Within 2 h of waking

Outdoor morning walk pairs activity with bright light, aiding circadian timing

Time to effect

Verbal memory and fluency

8–13 years

Shallower decline on word-recall and word-generation tests

Disabling dementia

4 years

Lower incidence in current dog owners over cohort follow-up

Walking volume and routine

2–4 weeks

Walking and routine change; no cognitive change detected over months

Benefits

Medium: Slower decline in verbal memory and fluency; lower incidence of disabling dementia in dog owners

Low: Higher habitual walking volume; companionship effects on loneliness; lower resting blood pressure and heart rate; lower cardiovascular and all-cause mortality

Speculative: Oxytocin-mediated damping of the stress axis; microbial exposure and immune regulation

Contraindications

Absent or non-functioning spleen (splenectomy, sickle cell disease, hyposplenism)

Absolute neutrophil count persistently below 500 per microlitre

Solid-organ transplantation within 6 months, or maintenance prednisone ≥20 mg daily

Severe persistent asthma (Global Initiative for Asthma step 4–5) with cat or dog sensitisation

Established osteoporosis (T-score ≤ −2.5) with prior fracture, for dogs above 15 kg or untrained

Advanced dementia (Clinical Dementia Rating ≥2) without a co-resident caregiver

Pregnancy, for litter-box handling specifically

Cell-killing chemotherapy and neutropenia, for waste handling while counts are lowest

Key Interactions

Immunosuppressants (tacrolimus, mycophenolate, prednisone ≥20 mg daily for ≥2 weeks), for litter handling

Tumour necrosis factor inhibitors (infliximab, adalimumab, etanercept)

Oral anticoagulants (warfarin, apixaban, rivaroxaban)

Sedative-hypnotics and anticholinergic drugs (zolpidem, diphenhydramine, oxybutynin)

Over-the-counter allergy and pain medication (diphenhydramine, chlorphenamine, ibuprofen)

Supplement interactions (melatonin, valerian, high-dose magnesium at night)

Supplements with additive effects (potassium, magnesium, beetroot nitrate, hibiscus, garlic)

Risk & Side Effects

Medium: Fall, fracture and head injury during dog walking; modestly higher depression risk in cat owners; asthma attacks in sensitised owners

Low: Zoonotic infection; cognitive effects of Toxoplasma gondii; higher odds of schizophrenia-related disorders in cat owners; sleep disruption from bed-sharing; caregiving strain and grief after the animal's death

Monitoring

Marker	Target	Why
Montreal Cognitive Assessment	≥26 of 30	Global cognitive screen, the primary endpoint
Verbal fluency, animal naming in 60 seconds	≥17 words	Where the pet-ownership signal appears
Usual gait speed, 4-metre walk	≥1.0 m/s	Slow gait precedes decline and predicts falls
Daily step count	7,000–10,000 steps/day	Quantifies dog-walking exposure objectively
Systolic blood pressure	110–125 mmHg	Midlife hypertension is a dementia risk factor
Bone mineral density T-score	≥ −1.0	Fracture consequence of a pull-related fall
High-sensitivity C-reactive protein	<1.0 mg/L	Inflammatory load; rises with airway allergy and infection
Absolute neutrophil count	1,800–7,000 per microlitre	Susceptibility to animal-borne infection
Total and animal-specific immunoglobulin E	Total <100 IU/mL; cat and dog specific negative	Allergic sensitisation driving airway inflammation and poor sleep
Toxoplasma gondii immunoglobulin G	Negative	Prior exposure before a cat enters the household

Cadence: Step count and sleep continuously or monthly; blood pressure every 3 months; cognitive and mobility measures at 12 months and annually thereafter; bone density every 2 years where abnormal at baseline.

Qualitative Assessment

Ease of word-finding in conversation, and whether names are retrieved more slowly than a year earlier
Subjective sleep quality and number of night-time awakenings attributable to the animal
Daytime energy and willingness to take the second walk rather than only the first
Mood, and whether time with the animal still registers as pleasurable rather than obligatory
Felt loneliness on days with and without human contact
Caregiving strain: whether veterinary costs or behavioural problems generate persistent worry

Pet Ownership to Preserve Cognitive Ability

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment