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Some types of cancers are known to be linked with genes or risky behaviors. But for many other types, a new study shows, the cause is basically bad luck. They are the result of mistakes, or mutations, that occur when stem cells divide to replace old cells. In the new study, researchers looked at previous research on how often stem cells in a particular type of tissue divide. Then they looked at the lifetime risk of cancer in those parts of the body. Cancers were most common in tissues that divided most often. These included bone marrow, source of cancers such as leukemia and lymphoma. In all, 22 of the 31 cancers studied were linked most closely with these random mutations as cells divided. Other examples included cancers of the ovary and pancreas. The other 9 cancers were linked with random mutations, too.

Cellphones and other “small screen” devices in the bedroom may be just as likely to reduce sleep time for children as TVs do, a new study finds. Previous research shows that children who have a TV in the bedroom tend to get less sleep. The new study was based on questionnaires answered by about 2,000 fourth- and seventh-grade students. They were asked about their sleep habits and their use of cellphones and other small devices, as well as TV. Students who slept near a small screen recorded 20.6 minutes fewer minutes of sleep on a typical weeknight than those who did not have a device nearby. Those who had a TV in the bedroom slept 18.0 minutes fewer each weeknight than those with no TV in the room. The amount of sleep lost was even greater for some groups. These included older children, Hispanics and non-Hispanic blacks. The journal Pediatrics published the study January 5.

Two experimental vaccines against Ebola and Marburg viruses are safe and produced an immune response in adults in Uganda, a new study finds. This is the first time these vaccines were tested in Africa. Earlier this year, similar results were reported in healthy U.S. adults. Researchers at the National Institute of Allergy and Infectious Diseases developed the vaccines. In the study, 108 healthy adults between the ages of 18 and 50 were randomly divided into four groups. One group got placebo injections. The other three groups got the Ebola vaccine, Marburg vaccine or both vaccines. The injections were given over eight weeks. Researchers followed the participants for two years. They found antibodies against the strain of the Ebola virus that caused the outbreak in West Africa in 17 of the people who got the Ebola vaccine alone and in 14 people who got both vaccines.

Teenagers whose mothers were depressed when the teens were between 6 and 10 years old are more likely to show signs of risky behavior, a new study finds. This included smoking, drinking, using marijuana and violent behavior. The study followed 2,910 pairs of mothers and their children in Canada, starting in 1994, when the children were between ages 2 and 5. The study continued until the children were ages 16 to 17. Every 2 years, mothers filled out questionnaires about themselves and their children. The children also filled out questionnaires beginning at age 10. Teens with depressed mothers in the teens’ middle childhood years were twice as likely to smoke cigarettes or use marijuana. They were also 1.4 times more likely to use alcohol and over 3 times more likely to use hallucinogens (for example, LSD).

Despite the risks of sedative drugs for older people, they are more likely to take these medicines than younger adults, a new study shows. The study focused on benzodiazepines. These drugs are used to treat anxiety and insomnia. Examples include alprazolam (Xanax), diazepam (Valium) and lorazepam (Ativan). The study was based on a U.S. prescription database for 2008. In that year, these medicines were prescribed for about 5% of adults ages 18 through 80. But among the oldest group, ages 65 through 80, nearly 9% took them. In all age groups, women were twice as likely as men to take sedatives. Almost one-third of older adults who used these medicines took them for at least 4 months. Long-term use may make them less effective. It also may increase the risk of addiction. Sedatives are known to increase the risk of falls, car accidents and confusion.