Animals and Cardiovascular Health. G.L. Jennings, Director, The Alfred & Baker Medical Unit, The Alfred Healthcare Group and The Baker Medical Research Institute. (Paper presented at the 7th International Conference on Human-Animal Interactions, Animals, Health and Quality of Life, September 6-9, 1995, Geneva, Switzerland).
Cardiovascular diseases which include coronary heart disease and stroke are the cause of almost half of all deaths in developed countries and are increasing dramatically in other countries with emerging economies. The changes in incidence of cardiovascular disease in various communities suggest that to a large extent the early cardiovascular deaths are preventable. Several countries including the United States and Australia experienced a substantial drop in cardiovascular deaths over the past 20 years. About a third of the fall can be attributed to improvements in medical treatment but the remainder is either unexplained or due to changes in risk factors that predispose to atheroschlerosis, the underlying cause of most cardiovascular disease.
The major known risk factors include smoking, high blood pressure and high blood cholesterol. Others are physical inactivity, diabetes, obesity, and other metabolic disorders. Psychological stress is less well established as a risk factor for atheroschlerosis but may be a precipitant of clinical events in individuals who have coronary artery disease. he precise contribution of all known risk factors to cardiovascular disease is not really known but estimates have been made that they may account for about one half. Clearly it is likely that there are other factors influencing rates of heart disease that are not yet considered as major risk factors.
In this light it is pertinent to consider the intriguing suggestion that there may be a relationship between ownership of animals and cardiovascular disease. We examined accepted cardiovascular risk factors in 5,741 healthy subjects attending a screening service. Pet owners had significantly lower systolic blood pressure and plasma triglycerides than non-owners. There were also significantly lower cholesterol levels in men but not women. Systolic blood pressure and triglyceride differences were only seen in women aged above 40 years. The differences in plasma triglycerides and systolic blood pressure were relatively modest averaging, in men, 13% and 2% respectively. When the high frequency of ownership of pets in the community is considered however (about 60% of households in Australia) they are large enough to be important to public health.
Associations such as these are open to various interpretations and do not prove that animal companionship per se lowers cardiovascular risk factors. We initially considered it more likely that other attributes that are more common in pet owners would account for the relationship. The socioeconomic profile of pet owners and non pet owners in our sample appeared similar and the lower risk factor levels were not due to smoking, body weight or dietary differences. Pet owners did take more regular exercise.
A recent national survey involving over 6,000 households indicated that dog owners attended a doctor in the previous year 8% less than non-dog owners. Cat owners had 12% fewer attendances than non-cat owners. This was reflected in lower rates of medication use for high blood pressure, cholesterol, sleeping difficulties or heart problems.
Clearly there is a need for further research to explain these and other observations. To date there is no data relating animal companionship to clinical outcomes or mortality and the mechanisms involved are unknown. The data to date do, however, provide support for the notion that individuals with a close relationship to animals carry a lower burden of some risk factors.
