Abstract
Background:
The presence of pets has been associated with reduction of stress and blood pressure and therefore may reduce the risk of cardiovascular diseases.
Methods:
Relative risks (RR) of all deaths, death due to myocardial infarction (MI), cardiovascular diseases (MI or stroke), and stroke during a 20 year follow-up were determined by Cox proportional hazards analysis for categories of cat or dog ownership among participants after adjustment for potential confounding variables.
Results:
Previous or present use of cats as domestic pets was reported by 2435 (55%) of the 4435 participants. After adjustment for differences in age, gender, ethnicity/race, systolic blood pressure, cigarette smoking, diabetes mellitus, serum cholesterol, and body mass index, a significantly lower RR for death due to MI was observed in participants with past cat ownership (RR, 0.63; 95% confidence interval [CI], 0.44 to 0.88) compared with those without cats as pet at any time. There was also a trend for decreased risk for death due to cardiovascular diseases among participants with past cat ownership (RR, 0.74; 95% CI, 0.55 to 1.0).
Conclusions:
A decreased risk for death due to MI and all cardiovascular diseases (including stroke) was observed among persons with cats. Acquisition of cats as domestic pets may represent a novel strategy for reducing the risk of cardiovascular diseases in high-risk individuals.
Keywords: cardiovascular diseases, cat ownership, national survey, stroke, myocardial infarction
Pet ownership has been related to reduction in stress, autonomic responses to cold and cognitive tasks, and need for medical attention associated with life stressors.1 Stress and its associated attributes have been related to the risk of cardiovascular diseases.2 Therefore, it is reasonable to assume that any social factors including pet ownership that reduces stress will eventually reduce cardiovascular events. The data regarding pet ownership and physical health has not been consistent. Friedmann et al.3 demonstrated that pet owners with medical heart conditions had a higher survival after 1 year of follow-up. A post-hoc analysis of Cardiac Arrhythmia Suppression Trial,4 again demonstrated lower mortality at 1 year after recruitment with pet ownership. However, there is paucity of data regarding this relationship derived from general population with almost no study addressing the risk of stroke. We performed this study to determine the effect of pet ownership on fatal cardiovascular events in a nationally representative cohort of persons followed for mean period of 13.4±3.6 years.
Methods
At baseline evaluation of National Health and Nutrition Examination Study (NHANES II) Follow-up Study5, any participant who reported any kind of allergy was queried further whether they owned or currently own a cat or a dog. Events of ischemic stroke, intracerebral hemorrhage (ICH), and myocardial infarction (MI) during followup were determined by death certificate International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9 CM) diagnosis codes: 433, 434, 436, 437.0, or 437.1 (for ischemic stroke); 431 to 432 (for ICH); and 410 to 414 (for MI). Subarachnoid hemorrhage was not included because of the small number of events (n=3) observed in NHANES II participants. Potential confounding variables were age, sex, race/ethnicity (African American, whites, other), systolic blood pressure, serum cholesterol level (<200 mg/dL, ≥200 mg/dL), body mass index, diabetes mellitus, and cigarette smoking (never, former, and current) at baseline. Relative risks (RR) for stroke and stroke types, and MI for cat and dog ownership (past and current) were estimated after adjustment for the established cardiovascular risk factors using Cox proportional hazard analyses. All analyses were performed using SAS (SAS Institute Inc. 2004, Cary, NC).
Results
Of the total of 14,407 NHANES participants, 4435 (31%) were inquired about pet ownership and were traced during each completed wave of follow-up. A total of 3592 (81%) and 2435 (55%) of the participants were dog or cat owners (either past or current), respectively. Of these, 1932 (44%) and 1015 (23%) were current dog and cat owners, respectively. Tables 1 and 2 demonstrate the baseline characteristics of 4435 participants according to cat or dog ownership. Age, cholesterol, race/ethnicity and cigarette smoking were associated with cat ownership. Same characteristics in addition to gender and systolic blood pressure were associated with dog ownership. After adjustment for potential confounders, a significantly lower RR for death due to MI was observed in participants with past cat ownership (RR, 0.63; 95% confidence interval [CI], 0.44 to 0.88) compared with those without cats as pet at any time (see Table 3). There was also a trend for increased risk for death due to cardiovascular diseases among participants without cats (RR, 0.74; 95% CI, 0.55 to 1.0). No protective effect of past and current cat ownership was observed for RR of stroke or stroke subtype. Dog ownership (see Table 3) was not associated with a reduced risk for death due to MI, or death due to cardiovascular diseases.
Table 1.
Baseline and clinical characteristics of participants according to past and current cat ownership (NHANES Mortality Follow-up Study)
| No history of cat ownership | Past cat ownership | Present cat Ownership | ||
|---|---|---|---|---|
| Baseline evaluation | ||||
| Number of participants | 2,000 | 1,420 | 1,015 | |
| Age (mean years ± SD)** | 52 ± 15 | 50 ± 15 | 47 ± 15 | |
| Systolic blood pressure (mean mmHg ± SD) | 131 ± 23 | 131 ± 23 | 130 ± 23 | |
| Serum Cholesterol (mean mg/dl ± SD)** | 224 ± 48 | 222 ± 49 | 219 ± 48 | |
| Body mass index (mean ± SD) | 25.8 ± 5.0 | 25.0 ± 5.2 | 25.6 ± 5.2 | |
| Gender | Women | 1150 (58%) | 839 (59%) | 594 (59%) |
| Race/ethnicity | Caucasian | 1703 (85%) | 1287 (91%) | 964 (95%) |
| African-American | 257 (13%) | 115 (8%) | 42 (4%) | |
| Others | 40 (2%) | 18 (1%) | 9 (1%) | |
| Cigarette smoking | Current | 673 (34%) | 492 (35%) | 389 (38%) |
| Past | 468 (23%) | 375 (26%) | 240 (24%) | |
| Never smoked | 859 (43%) | 553 (39%) | 386 (38%) | |
| Diabetes mellitus | Diabetic | 97 (5%) | 118 (5%) | 52 (5%) |
Symbols used:
p-value<0.05,
p-value <0.01
Abbreviations used: NHANES, National Health and Nutrition Examination Study; SD, standard deviation.
Table 2.
Baseline and clinical characteristics of participants according to past and current dog ownership (NHANES Mortality Follow-up Study)
| No history of dog ownership | Past dog ownership | Present dog ownership | ||
|---|---|---|---|---|
| Baseline evaluation | ||||
| Number of participants | 843 | 1,660 | 1,932 | |
| Age (mean years ± SD)** | 55 ± 15 | 52 ± 16 | 47 ± 14 | |
| Systolic blood pressure (mean mmHg ± SD) | 133 ± 25 | 132 ± 22 | 129 ± 22 | |
| Serum Cholesterol (mean mg/dl ± SD)** | 228 ± 47 | 224 ± 50 | 218 ± 48 | |
| Body mass index (mean ± SD) | 25.9 ± 5.5 | 25.6 ± 5.0 | 25.9 ± 5.0 | |
| Gender | Women | 296 (35%) | 724 (44%) | 832 (43%) |
| Race/ethnicity | Caucasian | 679 (81%) | 1482 (89%) | 1793 (93%) |
| African-American | 143 (17%) | 153 (9%) | 118 (6%) | |
| Others | 21 (2%) | 25 (2%) | 21 (1%) | |
| Cigarette smoking | Current | 233 (28%) | 538 (32%) | 783 (41%) |
| Past | 179 (21%) | 466 (28%) | 438 (23%) | |
| Never smoked | 431 (51%) | 656 (40%) | 711 (37%) | |
| Diabetes mellitus | Diabetic | 38 (5%) | 91 (5%) | 86 (4%) |
Symbols used:
p-value<0.05,
p-value <0.01
Abbreviations used: NHANES, National Health and Nutrition Examination Study; SD, standard deviation.
Table 3.
Multivariate-adjusted relative risks of fatal myocardial infarction, cardiovascular diseases, stroke, and ischemic stroke according to past and current cat and dog ownership.
| Participants | Sample size | No. of events | Event rate per 100 | Age-adjusted RR (95% CI) | Multivariate adjusted RR (95% CI) | p-value |
|---|---|---|---|---|---|---|
| Myocardial infarction | ||||||
| Participants without any cat ownership | 2000 | 115 | 6% | Reference | Reference | Reference |
| Participants with past cat ownership | 1420 | 46 | 3% | 0.65 (0.46–0.9) | 0.63 (0.44–0.88) | 0.008 |
| Participants with current cat ownership | 1015 | 37 | 4% | 1.01 (0.70–1.5) | 0.87 (0.60–1.3) | 0.4572 |
| Participants without any dog ownership | 843 | 52 | 6% | Reference | Reference | Reference |
| Participants with past dog ownership | 1660 | 70 | 4% | 0.82 (0.57–1.2) | 0.76 (0.53–1.1) | 0.1455 |
| Participants with current dog ownership | 1932 | 76 | 4% | 1.3 (0.90–1.8) | 1.1 (0.76–1.6) | 0.6270 |
| Cardiovascular diseases | ||||||
| Participants without any cat ownership | 2000 | 133 | 7% | Reference | Reference | Reference |
| Participants with past cat ownership | 1420 | 62 | 4% | 0.75 (0.56–1.0) | 0.74 (0.55–1.0) | 0.0501 |
| Participants with current cat ownership | 1015 | 45 | 4% | 1.0 (0.74–1.5) | 0.92 (0.65–1.3) | 0.6378 |
| Participants without any dog ownership | 843 | 60 | 7% | Reference | Reference | Reference |
| Participants with past dog ownership | 1660 | 92 | 6% | 0.93 (0.67–1.3) | 0.87 (0.63–1.2) | 0.4077 |
| Participants with current cat ownership | 1932 | 88 | 5% | 1.3 (0.93–1.8) | 1.1 (0.79–1.6) | 0.5563 |
| All strokes | ||||||
| Participants without any cat ownership | 2000 | 18 | 1% | Reference | Reference | Reference |
| Participants with past cat ownership | 1420 | 16 | 1% | 1.5 (0.74–2.9) | 1.5 (0.75–2.9) | 0.2607 |
| Participants with current cat ownership | 1015 | 8 | 1% | 1.4 (0.74–2.9) | 1.3 (0.54–2.9) | 0.5884 |
| Participants without any dog ownership | 843 | 8 | 1% | Reference | Reference | Reference |
| Participants with past dog ownership | 1660 | 22 | 1% | 1.7 (0.75–3.8) | 1.6 (0.69–3.5) | 0.2867 |
| Participants with current dog ownership | 1932 | 12 | 1% | 1.4 (0.57–3.5) | 1.2 (0.47–2.9) | 0.7247 |
| Ischemic stroke | ||||||
| Participants without any cat ownership | 2000 | 16 | 1% | Reference | Reference | Reference |
| Participants with past cat ownership | 1420 | 12 | 1% | Not adequate sample size | Not adequate sample size | Not available |
| Participants with current cat ownership | 1015 | 8 | 1% | Not adequate sample size | Not adequate sample size | Not available |
| Participants without any dog ownership | 843 | 6 | 1% | Reference | Reference | Reference |
| Participants with past dog ownership | 1660 | 18 | 1% | 1.9 (0.74–4.7) | 1.7 (0.65–4.2) | 0.285 |
| Participants with curent dog ownership | 1932 | 12 | 1% | 2.0 (0.73–5.3) | 1.7 (0.61–4.5) | 0.3212 |
| All cause mortality | ||||||
| Participants without any cat ownership | 2000 | 405 | 20% | Reference | Reference | Reference |
| Participants with past cat ownership | 1420 | 255 | 18% | 1.0 (0.85–1.2) | 1.1 (0.85–1.2) | 0.9925 |
| Participants with present cat ownership | 1015 | 174 | 17% | 1.3 (1.1–1.5) | 1.1 (0.93–1.3) | 0.2373 |
| Participants without any dog ownership | 843 | 191 | 23% | Reference | Reference | Reference |
| Participants with past dog ownership | 1660 | 341 | 21% | 1.1 (0.88–1.3) | 0.97 (0.81–1.2) | 0.7634 |
| Participants with present dog ownership | 1932 | 302 | 16% | 1.2 (1.0–1.5) | 1.0 (0.85–1.2) | 0.8140 |
Abbreviations: RR, relative risk; CI, confidence interval.
Multivariate analysis is adjusted for differences in age, gender, ethnicity/race, systolic blood pressure, cigarette smoking, diabetes mellitus, serum cholesterol, and body mass index.
Discussion
We found an independent association between cat ownership and risk of fatal MIs in the present cohort study. The protective effect may be related to a spontaneous relaxing effect with buffering effect on autonomic reactivity to acute stressors, and/or classical conditioning of relaxing response.1, 6, 7 We cannot exclude that this effect may be an indirect effect i.e. personalities of cat owners may have traits that are protective towards cardiovascular diseases independent of cat ownership. The study did not allow us to quantitate cat exposure in terms of years, intensity of physical interaction, and nature of interaction (tactile or visual). We only found the relationship between past cat ownership and fatal cardiovascular events. It is possible that cat ownership at an early age in life may be more protective than at a later age when sub clinical cardiovascular disease has already occurred. We did not see a protective effect of cat ownership on the risk of stroke. It maybe the number of stroke events may be too small to adequately assess the relationship. Furthermore, the role of cardiovascular reactivity in precipitating an event is less established in stroke than MI. A similar effect was not seen with dogs. It is presumable the dogs vary considerably in characteristics thereby the effect is not homogenous. The data was acquired only for participants who reported any allergic response. It remains unclear whether the relationship between cat ownership and cardiovascular disease would be similar among persons without any allergic response. In a previous analysis from the NHANES II mortality follow-up study, no association was found between allergen skin reaction at baseline and subsequent mortality although data was not examined according to pet ownership status.8 We used primary ICD-9-CM codes from death certificates to identify events. On the basis of results of previous studies, we think that hospital discharge or death certificate diagnoses are sufficiently accurate to justify their use in present study.9–11 Probably more important, the validity of ICD-CM diagnoses does not differ by strata defined by pet ownership. The results need to be confirmed in other studies with better and controlled quantification of cat exposure. A previous study among hypertensive persons randomized to pet adoption or control group demonstrated lower blood pressure reactivity to stress at 6 months.12 While no data exists for protective effect on cardiovascular events, acquisition of cats as domestic pets may represent a novel strategy for reducing the risk of cardiovascular diseases in high-risk individuals.
Acknowledgments
Dr. Qureshi is supported in part by the National Institutes of Health’s grant RO-1-NS44976-01A2 and American Heart Association’s Established Investigator Award 0840053N.
References
- 1.Virues-Ortega J, Buela-Casal G. Psychophysiological effects of human-animal interaction: Theoretical issues and long-term interaction effects. J Nerv Ment Dis. 2006;194:52–57. doi: 10.1097/01.nmd.0000195354.03653.63. [DOI] [PubMed] [Google Scholar]
- 2.Dimsdale JE. Psychological stress and cardiovascular disease. J Am Coll Cardiol. 2008;51:1237–1246. doi: 10.1016/j.jacc.2007.12.024. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Friedmann E, Katcher AH, Lynch JJ, Thomas SA. Animal companions and one-year survival of patients after discharge from a coronary care unit. Public Health Rep. 1980;95:307–312. [PMC free article] [PubMed] [Google Scholar]
- 4.Friedmann E, Thomas SA. Pet ownership, social support, and one-year survival after acute myocardial infarction in the cardiac arrhythmia suppression trial (cast) Am J Cardiol. 1995;76:1213–1217. doi: 10.1016/s0002-9149(99)80343-9. [DOI] [PubMed] [Google Scholar]
- 5.Loria CM, Sempos CT, Vuong C. Plan and operation of the nhanes ii mortality study, 1992. Vital Health Stat 1. 1999:1–16. [PubMed] [Google Scholar]
- 6.Vormbrock JK, Grossberg JM. Cardiovascular effects of human-pet dog interactions. J Behav Med. 1988;11:509–517. doi: 10.1007/BF00844843. [DOI] [PubMed] [Google Scholar]
- 7.Allen KM, Blascovich J, Tomaka J, Kelsey RM. Presence of human friends and pet dogs as moderators of autonomic responses to stress in women. J Pers Soc Psychol. 1991;61:582–589. doi: 10.1037//0022-3514.61.4.582. [DOI] [PubMed] [Google Scholar]
- 8.Gergen PJ, Turkeltaub PC, Sempos CT. Is allergen skin test reactivity a predictor of mortality? Findings from a national cohort. Clin Exp Allergy. 2000;30:1717–1723. doi: 10.1046/j.1365-2222.2000.00971.x. [DOI] [PubMed] [Google Scholar]
- 9.Broderick J, Brott T, Kothari R, Miller R, Khoury J, Pancioli A, Gebel J, Mills D, Minneci L, Shukla R. The greater cincinnati/northern kentucky stroke study: Preliminary first-ever and total incidence rates of stroke among blacks. Stroke. 1998;29:415–421. doi: 10.1161/01.str.29.2.415. [DOI] [PubMed] [Google Scholar]
- 10.Iso H, Jacobs DR, Jr, Goldman L. Accuracy of death certificate diagnosis of intracranial hemorrhage and nonhemorrhagic stroke. The minnesota heart survey. Am J Epidemiol. 1990;132:993–998. doi: 10.1093/oxfordjournals.aje.a115742. [DOI] [PubMed] [Google Scholar]
- 11.Pietila K, Tenkanen L, Manttari M, Manninen V. How to define coronary heart disease in register-based follow-up studies: Experience from the helsinki heart study. Ann Med. 1997;29:253–259. doi: 10.3109/07853899708999343. [DOI] [PubMed] [Google Scholar]
- 12.Allen K, Shykoff BE, Izzo JL., Jr Pet ownership, but not ace inhibitor therapy, blunts home blood pressure responses to mental stress. Hypertension. 2001;38:815–820. [PubMed] [Google Scholar]