Planning to pull an all-nighter cramming for a big exam? New research suggests that getting a good night’s sleep might serve you better.
Researchers at Harvard Medical School studied the effect of sleep deprivation on learning and memory. In work partially supported by NIH’s National Institute of Mental Health, they trained 133 people between the ages of 18 and 25 in a visual discrimination test. The test involved a “target” screen which showed either an “L” or a “T” in the center and three diagonal bars in one section aligned either horizontally or vertically, against a background of horizontal bars. They were then shown a blank screen and finally a mask screen, filled with angular symbols. The people had to recount which letter they’d seen, and which way the bars had been aligned. This was done repeatedly to get a good sense of how the people performed.
There was no significant improvement in performance when testing was done on the same day as training. But testing on the day following training, after a night of sleep, brought significant improvements. The researchers think that the people’s brains somehow processed the training while they were asleep.
To support this interpretation, they deprived one group of sleep the night after training. They let them have two nights of recovery sleep and then tested them once they were as alert as another group that had slept all along. The sleep-deprived people showed no significant improvement over their training sessions, and didn’t score nearly as high as the other group. This experiment showed that the night of sleep right after training was crucial for processing what these people had learned, and that catch-up sleep couldn’t make up for the loss of that first night.
The researchers conclude that sleep is important in consolidating, integrating and maintaining memories. Add this to the growing body of evidence showing how your brain processes lessons and experiences from the day while you are asleep, and it’s hard to ignore the importance of getting a good night’s sleep. — a report from The NIH Word on Health, April 2001 Nature Neuroscience 3,12:1237-1238
The Unpredictable Fertile Window
Some couples trying to become pregnant, and others trying to avoid pregnancy, time their sexual intercourse by the calendar, trying to predict the days in a woman’s menstrual cycle when she is fertile. A new study emphasizes how unpredictable this method can be.
Scientists used to think that most woman were fertile between days 10 and 17 of their menstrual cycles (day 1 is defined as the day menstrual bleeding begins). This “window” was thought to span several days before and after ovulation. However, these conclusions were drawn from fairly crude measurements of ovulation like looking for changes in body temperature.
Dr. Allen Wilcox, chief of epidemiology at NIH’s National Institute of Environmental Health Sciences, and his colleagues had already framed the fertile window more precisely in previous studies. They found that there are generally six days in the average woman’s menstrual cycle when sexual intercourse can result in pregnancy: the five days before ovulation (the release of an egg from an ovary) and the day of ovulation itself.
In the new study, the team set out to find if the timing of the fertile window is as consistent as once thought. Over two hundred women between the ages of 25 and 35 — when menstrual cycles are thought to be most regular — were tested for their day of ovulation by measuring their urine daily for levels of the female sex hormones estrogen and progesterone. An abrupt change in the ratio between these hormones signals ovulation. The scientists found that only about 30% of the women had their fertile window entirely between days 10 and 17. An estimated 2% of the women were actually in their fertile window by the fourth day of their cycle, and 17% by the seventh day. One woman in the study gave birth to a healthy infant from an egg released on her eighth day. Some women reached their fertile window much later, as late as the fifth week of their cycle. Even women who said their menstrual cycles were regular had a chance of being in their fertile window on the day they expected their next cycle to begin.
The researchers concluded that fertile windows are very difficult to predict. According to Dr. Wilcox, “If the average healthy couple wants to get pregnant, they are just as well off to forget ‘fertile windows’ and simply engage in unprotected intercourse two or three times a week.” By the same token, no timing method for preventing pregnancy can be completely effective. If you need for some reason to rely exclusively on natural forms of birth control, make sure to arm yourself with as much knowledge as possible about the time of your ovulation. — a report from The NIH Word on Health, April 2001 British Medical Journal 321:1259-1262
For more information about conception and birth control, visit the MEDLINEplus web page at <http://www.nlm.nih.gov/medlineplus/birthcontrolcontraception.html>.
Inhaled Steroids in Children with Asthma
Children with asthma often have to take inhaled corticosteroids like budesonide for long periods of time. Parents worry about the long-term effects of these drugs on their children’s growth. A new study funded by NIH’s National Heart, Lung and Blood Institute (NHLBI) lets them breathe a little easier.
About five million children in the U.S. have asthma. It is a disease in which there is chronic inflammation of the airways in the lungs. The airways narrow when exposed to certain irritants like viruses, smoke, or pollen and make it hard to breathe, causing coughing, wheezing, chest tightness, and shortness of breath. Asthma can’t be cured, but you can take medicines to control it.
The new study, carried out by The Childhood Asthma Management Program Research Group, randomly assigned 1041 children from five to twelve years of age with mild to moderate asthma to three different groups. All used the standard type of medicine to treat an asthma attack, but for long-term treatment one group took the corticosteroid budesonide twice a day, one group took a non-steroidal anti-inflammatory drug called nedocromil, and one took a placebo. The children were followed for four to six years.
Asthma was controlled best in the group taking budesonide. That group had fewer urgent-care and hospital visits, more episode-free days, and less need for other potent drugs to treat their asthma. The nedocromil group showed improvement in some respects, but the results weren’t nearly as strong as with budesonide.
Previous studies had raised concerns that children taking corticosteroids for long periods of time could have stunted growth. This study showed that those taking budenoside had a slower growth rate initially — they were about 3/8 inch shorter than the children in the other two groups at the end of the first year. But afterwards, the growth rate for those on budesonide was identical to the other two groups. Tests at the end of the study suggest that the children taking the corticosteroid will likely reach their normal heights as adults.
The researchers concluded that continuous daily treatment with inhaled budesonide leads to better control of asthma in children over five years of age who have mild to moderate asthma, with the only side effect being a small and temporary slowing of growth. An editorial that accompanied the published study noted that it does not tell us about the use of the medication in children who are either younger than five or who have very mild asthma. — a report from The NIH Word on Health, April 2001 The New England Journal of Medicine 343:1054-1063.
For more information on asthma, visit <http://rover2.nhlbi.nih.gov/health/public/lung/index.htm#asthma>, call the NHLBI Information Center at 301-592-8573, or write to NHLBIinfo@rover.nhlbi.nih.gov.
Air Pollution Slows Children’s Lung Function Growth
The damage air pollution can inflict on the lungs has long been known. Much of this damage isn’t thought to be permanent as long as the person isn’t continually exposed to the pollution. A new study focusing on children, however, has found that air pollution affects their lungs’ development, an effect that may last a lifetime.
A group of scientists supported in part by NIH’s National Institute of Environmental Health Sciences studied 3,035 children in grades four, seven and ten in twelve communities around Los Angeles, California. They looked at the children’s medical histories, where they lived, and how much time they spent outdoors. The children were tested annually for their lung function, a measure of how much air their lungs could exhale. Then these results were compared to air pollution data collected in the twelve communities. This study is still ongoing, and will last for a total of 10 years; the scientists eventually hope to see how exposure to air pollution during childhood affects lung function in adulthood.
Over the four years covered in this report, the lung function growth rate of children in the most polluted community was about 10 percent lower than that of children in the least polluted community. Adding to the evidence that the effect was caused by outdoor air pollution was the observation that the children who spent more time outdoors suffered the most harm. Ozone, an outdoor air pollutant already known to cause other lung problems, did not appear to be involved. Slower lung function growth was correlated with nitrogen dioxide, airborne microscopic particles, and acid vapor. These pollutants all come either directly or indirectly from the burning of fossil fuels, such as in a car engine or an industrial plant.
The researchers could not pin the blame on any single pollutant in the study. Indeed, there may be pollutants they didn’t measure that are also contributing to the effect. Whatever the culprits may be, Dr. W. James Gauderman, one of the authors of the study, argues, “Our results indicate that continued reduction of air pollution, through the efforts of both regulators and the public, will lead to improved health in our children.” — a report from The NIH Word on Health, April 2001 American Journal of Respiratory and Critical Care Medicine 162:1383-1390.
For more information about air pollution and health, visit the MEDLINEplus web page at <http://www.nlm.nih.gov/medlineplus/airpollution.html>.
