From Harvard Medical School Newsletter: (Sept. 2015)
Having a dog can help your heart — literally
Dog lovers know how much warmth and comfort their canine companions add to their lives. But they might not know that a growing body of evidence suggests that having a dog may help improve heart health.
Pet ownership, especially having a dog, is probably associated with a decreased risk of cardiovascular disease. This does not mean that there is a clear cause and effect relationship between the two. But it does mean that pet ownership can be a reasonable part of an overall strategy to lower the risk of heart disease.
Several studies have shown that dog owners have lower blood pressure than non-owners — probably because their pets have a calming effect on them and because dog owners tend to get more exercise. The power of touch also appears to be an important part of this "pet effect." Several studies show that blood pressure goes down when a person pets a dog .
There is some evidence that owning a dog is associated with lower Cholesterol and Triglyceride levels. A large study focusing on this question found that dog owners had lower Cholesterol and Triglyceride Levels.
A large study focused on this question found that dog owners had lower Cholesterol and Triglyceride levels that non-owners, and that these differences weren't explainable by diet, smoking, or Body Mass Index (BMI). However, the reason for these differences is sill not clear.
Dogs' calming effect on humans also appears to help people handle stress. For example, some research suggests that people with dogs experience less cardiovascular reactivity during times of stress. That means that their heart rate and blood pressure go up less and return to normal more quickly, dampening the effects of stress on the body.
If you own a dog or are thinking about it, the potential benefits for your heart health are a nice plus. However, pets should not be adopted for the primary purpose of reducing heart disease risk. And definitely don't add a dog to your life if you're not ready or able to take care of one, including making sure it gets enough exercise.