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Not all smokers get lung cancer. And some people can quit more easily than others. Some of the reasons may be genetic, new research shows. The studies found different versions of genes that increase the risk of both lung cancer and smoking addiction. Smokers who get the gene variants from one parent have a 30% greater risk of lung cancer. The risk goes up 80% for smokers who get the genes from both parents. Another study found that people with these genes get addicted more easily and smoke more. Three different studies found the variant genes on chromosome 15. USA Today and the Associated Press wrote about the studies April 3. They were published in the journals Nature and Nature Genetics.

Treating children early for attention deficit-hyperactivity disorder (ADHD) does not raise their risk of drug abuse, a study finds. But starting treatment later may increase that risk. The 17-year study included 176 boys with ADHD. All were treated with stimulant medicines. They received Ritalin or a generic version of it. Some boys started taking it at ages 6 or 7. They went on to have no more drug abuse problems than a comparison group of healthy children. But boys who began treatment at ages 8 to 12 did have higher drug abuse rates later on. The study was published April 1 in the American Journal of Psychiatry.

Corneas from older donors may be as useful for transplant as younger ones, a study suggests. The study took a look at results of 1,000 cornea transplants. People were divided into two groups. One group received corneas from donors ages 12 to 65. The other group received older organs. The donors were ages 66 to 75. In 86% of both groups, the transplants still were functioning five years later. The Associated Press wrote about the study April 1. It was published in the journal Ophthalmology.

Mouth breathing isn’t needed for most CPR, the American Heart Association says. Instead, the group says it’s best just to call 911 and then press hard and fast on the person’s chest. Hands-only CPR requires about 100 pushes per minute until help arrives. This method applies only for adults who collapse and stop breathing. They probably have had a cardiac arrest — when the heart stops beating. Pushing on the chest helps the blood circulate. Children who collapse are more likely to need mouth-to-mouth breathing as well, the group says. The Associated Press reported on the new guidelines April 1.

A two-drug cholesterol pill does not protect arteries any better than one drug, a study finds. The pill is called Vytorin. It contains Zocor, a statin drug that lowers LDL cholesterol. It also contains Zetia, which lowers LDL in a different way. People were randomly assigned to take either Zocor or Zocor plus Zetia. Plaque buildup in arteries was about the same in the two groups. This occurred even though the two drugs reduced LDL more than Zocor did. The Associated Press reported on the study March 31. It was presented at a meeting of the American College of Cardiology. It also was published online by the New England Journal of Medicine.

Having a big belly in middle age could increase your risk of dementia in old age, a study suggests. More than 6,500 men and women in their 40s were measured front to back using calipers. A distance of more than 10 inches was considered high. About 35 years later, nearly 1 in 6 people had developed Alzheimer’s disease or another form of dementia. People who had big bellies in their 40s were nearly twice as likely to have dementia. This was true even for people who had normal body weight but extra fat in the belly. Overweight people were even more likely to have dementia if their weight was concentrated in the belly. The Associated Press wrote about the study March 27. It was in the journal Neurology.

A computed tomography (CT) scan can help predict the risk of a heart attack, a study finds. But it’s unclear if the scans are worth the cost, $300 to $600. Researchers gave CT scans to more than 6,700 men and women. They were white, black, Chinese and Hispanic. Some people’s scans showed large amounts of calcium in the walls of the heart arteries. They were 10 times more likely to have major heart events in the next four years as those with the least calcium in their arteries. Events included heart attacks, heart-related death, major chest pain and procedures to unblock heart arteries. HealthDay News wrote about the study March 26. It was published in the New England Journal of Medicine.