We know that smoking is bad news. Whether you're smoking yourself, sitting next to someone who is smoking, or even exposed to the tobacco residue (third-hand smoke) left behind, the stuff that's in cigarettes and other tobacco products can kill you. According to the American Cancer Society, "secondhand smoke immediately affects the heart and blood circulation in a harmful way. Over a longer time it also causes heart disease and lung cancer." A new study from the University of Turku in Finland shows that the damage caused by secondhand smoke may be affecting kids even earlier than once thought.

Finnish researchers have found that the damage caused by secondhand tobacco smoke starts in childhood and causes measurable damage by the teen years. Children as young as 13 who have evidence of secondhand smoke in their blood also have visibly thicker arteries.

For the study, researchers studied 494 children aged 8 to 13 taking part in ongoing research on heart disease. They measured levels of cotinine, a byproduct of nicotine that is found in the blood after someone breathes in tobacco smoke. After dividing the children into groups with high, intermediate and low cotinine levels, the kids were given ultrasounds to measure the thickness of the aorta and of the carotid artery in the neck (thicker arteries are a sign of atherosclerosis.)

The children with the most cotinine in their blood had carotid artery walls that were, on average, 7 percent thicker than the children with the lowest cotinine levels, and their aortas were 8 percent thicker.

Next, the researchers tested the flexibility of the arteries in the arm, another measure of blood vessel health and heart disease risk. This measurement, called brachial artery flow-mediated dilation, was 15 percent lower in teenagers with the highest levels of cotinine, they found. Measures of cholesterol showed unhealthier levels among the children with more smoke in their blood.

Yet another good reason to stay away from cigarettes and make sure your kids do the same. If you still smoke, check out Smokefree.gov to find out how to quit. Today.

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