Current estimates indicate that between 30 and 40 percent of all pet dogs live in a home that contains at least one person who smokes. A recent study suggests that these dogs are at risk of premature aging and inflammation, which may well shorten their life span.
Although there is extensive research on the effects of second-hand tobacco smoke in human beings, there has not been a lot of research on its effects on the health of dogs. From the research that exists there has been some suggestion that the risk of cancer is somewhat higher for dogs who live in a household which contains a smoker (click here for more about that). However, new research by Natalie Hutchinson from the School of Veterinary Medicine at the University of Glasgow suggests that dogs who are exposed to tobacco smoke show a number of biological markers that are normally seen in aging dogs and may ultimately be associated with an early death.
This research, which was published as a doctoral thesis, involved a community-based sample of dogs, approximately half of whom lived in smoking homes and half in non-smoking homes. The dogs were observed over a period of 12 months. The first step was to determine whether the dogs living in a household with a smoker actually were absorbing chemicals from the tobacco smoke in their environment. This was done by looking at the hair of the dogs. One important chemical biomarker is nicotine and another is cotinine (which is an alkaloid found in tobacco and also appears when an animal metabolizes nicotine). The level of these biomarkers was higher in dogs coming from smoking households and was related to the amount of smoking going on around the dogs.
The number of analyses and tests described in this nearly 600-page report are extensive and complex. However, there are a few findings which are significant and easily described. These are based on analysis of samples of tissue taken from the mouth, muscles, and urogenital regions of the dogs. In this case the researcher was trying to measure the lengths of telomeres, which are a marker of physiological aging.
Our genetic material, specifically DNA, is stored in bodies called chromosomes. Telomeres are the protective caps on the ends of these chromosomes. In young humans, for instance, telomeres are about 8,000 to 10,000 nucleotides long. However, over time they grow shorter. This comes about because the telomeres get reduced in size with each cell division. This is important because when the telomeres reach a critically short length the cell stops dividing and it might even die. The erosion of telomeres over time has been linked to aging and disease risks including things like cancer. In effect, this gradual shortening of the telomeres suggests that our cells are pre-programmed to a limited number of cell divisions which we cannot exceed. This is sometimes called the Hayflick limit, after its discoverer Leonard Hayflick. Some people believe that the Hayflick limit is a measure of the maximum lifespan of any animal.
The bad news is that telomeres can be shortened by other things besides cell simple division. One of the important influences is oxidative stress, which is essentially an imbalance between the production of free radicals and a body's ability to readily detoxify or repair the resulting damage. Research has demonstrated that cigarette smoking produces oxidative stress, which might also mean that it can possibly reduce the length of telomeres.
One of the major findings of this new research is that dogs living with smokers have shorter telomeres, suggesting that at the physiological level these dogs are acting as if they had undergone premature aging. It has already been shown that there is a relationship between telomere shortening and lifespan, hence these dogs will likely have shorter lives.
There is other evidence that dogs that live in smoking households are in poorer health. This involves measurement of a glycoprotein called clusterin. This protein helps to protect cells that are under stress from a variety of inflammatory sources. Since the level of clusterin rises as more cells come under attack, it has been proposed that clusterin can also serve as a biomarker of disease. These new data demonstrate that the amount of clusterin in dogs exposed to environmental tobacco smoke is considerably higher, suggesting that their bodies are under attack at a cellular level.
There are other significant findings in this extensive piece of research, however all trend in the same direction. Smoking is not only shortening the life span of the human smokers in a household, but it is likely doing the same thing for their canine companions. Tobacco smoke in the environment is prematurely aging dogs at the cellular level and bringing them closer to death.
Stanley Coren is the author of many books including: Gods, Ghosts and Black Dogs; The Wisdom of Dogs; Do Dogs Dream? Born to Bark; The Modern Dog; Why Do Dogs Have Wet Noses? The Pawprints of History; How Dogs Think; How To Speak Dog; Why We Love the Dogs We Do; What Do Dogs Know? The Intelligence of Dogs; Why Does My Dog Act That Way? Understanding Dogs for Dummies; Sleep Thieves; The Left-hander Syndrome
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Hutchinson, Natalie (2017) Evaluating the impact of environmental tobacco smoke on biological age markers: a canine model. University of Glasgow PhD thesis. http://theses.gla.ac.uk/8371/