THURSDAY, Dec. 20 (HealthDay News) -- Sex education programs do work to help discourage many teens from becoming sexually active before age 15, according to data released Wednesday by the U.S. Centers for Disease Control and Prevention (CDC).

Formal programs -- such as those presented in schools and church groups -- did appear to delay onset of sexual activity. For example, teen girls in the nationally representative sample were 59 percent less likely to start having sex before age 15 if they had received sex education, while teen boys were 71 percent less likely, the study found.

"We were obviously hoping to find that sex education is effective. We're glad to see the strong associations," said lead author Trisha Mueller, a CDC epidemiologist. She emphasized that in order to be successful, sex education should take place before young people become sexually active.

Mueller's team also learned that teen boys who attended school were almost three times more likely to use contraception if they had attended a sex education program, compared to those who had not.

However, attendance at a sex education class did not seem to impact girls' use of birth control, the survey found.

The survey did not differentiate between programs that emphasized abstinence and those that educated about contraception. Instead, researchers focused only on whether the teens had ever attended any sex education program in a formal setting, such as school or church.

The study was expected to be published in the January issue of the Journal of Adolescent Health.

According to earlier, 2005 data available from the CDC, 47 percent of high school students said they had already had sex. Of those who were currently involved in a sexual relationship, one-third said they were not using a condom.

Curious about the effectiveness of sexual education on these behaviors, Mueller and colleagues examined data from more than 2,000 teen boys and girls between 15 and 19 years of age who participated in the door-to-door 2002 National Survey of Family Growth.

"Formal sex education is beneficial for youth who are considered to be at-risk," noted Mueller, who cited as an example the 88 percent reduced risk of initiation sex before age 15 among urban black females who had received any sex education. Urban black teen girls who were still in school at the time of the survey had a 91 percent reduced risk of initiation sex before age 15, the survey found.

The research also showed that boys living in single-parent households were more likely to delay sex past age 15 if they had attended a sex education class.

Mueller and her team were interested in teen sexual decision-making before and after the age of 15, because the federal governments' Healthy People 2010 initiative treats 15 as a dividing line. Healthy People 2010 sets a wide array of health goals for states and communities to achieve over the first decade of this century. One of its objectives: to reduce the number of teens under age 15 who are having sex for the first time.

"First and foremost, the report makes clear that the timing of sex education is quite important. That is, providing sex education to young people at an early age seems quite important in helping delay sexual activity," said Bill Albert, deputy director of the Washington, D.C.-based National Campaign to Prevent Teen and Unplanned Pregnancy.

The researchers said the study could not explain why sex education might have a stronger effect in delaying sex among teen boys and black girls, but Albert offered an explanation.

"It is the case that declines in sexual activity among teen boys, as opposed to girls, and African-American teen girls, as opposed to other racial/ethnic groups, have been much more dramatic over the past decade. This may, in part, explain why the effect of sex education seems stronger. It may also be that concern about HIV/AIDs may be particularly strong among these two groups," said Albert.

However, certain sub-populations of teens deserve further research, said Mueller. The data suggested that both rural, white teen girls and white or Hispanic teen girls who had dropped out of school might be more likely to have sex before age 15 if they had sex education, but Mueller said the number of people in those groups in the study was so small that the results could be a statistical fluke.

"They were kind of opposite findings," said Mueller, who acknowledged that "some subgroups may not benefit from sex ed the same way as the larger group of teens."

This research comes in the wake of data released Dec. 5 by the CDC showing that the annual rate of births to teens has increased for the first time in 14 years. Between 2005 and 2006, the birth rate for girls 15 to 19 rose 3 percent -- from 40.5 births per 1,000 in 2005 to 41.9 per 1,000 in 2006.

Considering both studies, Albert said, "The early wins may have been won. Future efforts may well have to be more intense, focused, and creative if the nation is to make continued progress in reducing teen pregnancy and childbearing. Put another way, yesterday's way of doing business will no longer suffice."

More information

To find more data about teenagers and sexual decision-making, visit the U.S. Centers for Disease Control and Prevention.

THURSDAY, Dec. 20 (HealthDay News) -- Women who've had a miscarriage or an abortion are much more likely than women who haven't to experience a low-birthweight or premature baby in the future, new research shows.

A team at Virginia Commonwealth University looked at data on more than 45,500 mother-and-child pairs enrolled in the United States Collaborative Perinatal Project.

About 40 percent of the mothers had one or two children, and almost two-thirds of the mothers were between ages 20-29. The researchers found that rates of low-birthweight (under 2,500 grams or 5.5 pounds) and premature babies (less than 37 weeks gestation) were highest among women who were black, young or old, poorly educated, and unmarried.

The study also found that women who'd had one, two, or three or more miscarriages or abortions in the past were almost three, five and nine times, respectively, more likely than normal to have an underweight baby.

Women who'd had one miscarriage or abortion were 67 percent more likely to have a premature baby, while women who'd had three or more miscarriages or abortions were more than three times as likely to have a premature baby, compared to women who hadn't had a miscarriage or an abortion.

The study is published in the Journal of Epidemiology and Community Health.

The researchers noted that previous studies have been inconclusive, with some reporting no increased risk and others identifying a significantly increased risk of low-birthweight or premature babies among women who've had a miscarriage or abortion. Despite the conflicting evidence, women and doctors need to be aware of the potential risks, the authors concluded.

More information

The March of Dimes has more about low birthweight  .

MONDAY, Dec. 3 (HealthDay News) -- Love not only makes the world go round, it may make it greener, too.

Rising divorce rates mean that fewer people are living in each household, causing them to take up more space and consume more energy and water, a new study suggests.

"People talk about divorce hurting the children. Divorce also has an impact on the environment," said Jianguo "Jack" Liu, senior author of the study and the Rachel Carson chair in sustainability at Michigan State University. "Nobody knew about it."

Liu started doing research in panda reserves in China years ago. "In the reserves, there are not only pandas but also more than 4,000 people," he said. "Surprisingly, the number of households increased much faster than the number of people in the last three decades, so we were wondering if that was true at the global level."

Pandas are naturally solitary creatures, living separately from each other. Humans, on the other hand, tend to be more social. But when the social bond falls apart and people start living more like pandas, the drain on the environment is greater, Liu said.

"If you increase the number of households, you need more land to build houses, you need to have energy to cook food and to heat in the winter time," Liu explained. "If you need more land, then you cut down the forest and cut down trees for fuel, you destroy more habitat for the pandas. There's a direct connection."

In China and elsewhere, one important reason for this increase in the number of households is divorce -- although other reasons include fewer generations living under the same roof and people staying single longer. In the United States, the households headed by a divorced person increased from 5 percent in 1970 to 15 percent in 2000, while the proportion of married households decreased from 69 percent to 53 percent during the same time period. In China, almost 2 million couples untied the knot in 2006.

For this study, published online in this week's edition of the Proceedings of the National Academy of Sciences, Liu and his team compared differences between married and divorced households to see if they varied in their consumption of three important but increasingly limited resources: land (measured by number of rooms in the house), electricity and water.

Among their findings:

• In 12 countries studied between 1998 and 2002, there were 1.1 to 1.8 fewer people living in an average divorced household, compared to an average married household. Another way to say it: The average divorced household was 27 percent to 41 percent smaller than the average married household.
• If divorced households in these 12 countries (which included the United States, Brazil, Greece, Mexico and South Africa) had combined to become the same size as a married household, there would have been 7.4 million fewer households overall.
• In the 12 countries, divorced households occupied 33 percent to 95 percent more rooms per person than married households. Expanding divorced households to the size of married households would have resulted in 8.4 million to 37.5 million fewer rooms in less developed and westernized countries, respectively.
• In the United States alone in 2005, 38.5 million rooms would have been unnecessary (along with heating and lighting costs) if divorced households combined to become the same size as married households.
• Also in the United States in 2005, divorced households used 73 billion kilowatt-hours of electricity and 627 billion gallons of water that could have been saved if the divorced households had remained the same size as married households.

As with so many things, love may be the solution.

"People can try to stay married and not get divorced," Liu said. "Or if there's no way two people can stay together then get divorced, then get remarried quickly or live together with other people."

Liu's study showed that, after remarriage, average household size and the number of rooms per person returned to the level of households that had stayed married the whole time.

To Dr. Maureen Lichtveld, chairwoman of the department of environmental health sciences at Tulane University School of Public Health and Tropical Medicine, the findings are another example of the inextricability of humans and their habitat.

"In order to find sustainable solutions for environmental health issues, we must take a holistic approach and that holistic approach requires looking at both the environment in the traditional sense of the word and the environment from the human health aspect," she said.

More information

To measure your own ecological footprint, take this quiz from the Global Footprint Network  .

FRIDAY, Nov. 2 (HealthDay News) -- Women who followed at least five certain lifestyle and diet behaviors were about 80 percent less likely to have infertility from ovulatory disorders than women who followed none of the behaviors, a Harvard study concludes.

The analysis of 17,544 married women participating in the ongoing Nurses' Health Study II found those with the highest fertility scores: ate less trans fat and sugar from carbohydrates; consumed more protein from vegetables than from animals; ate more fiber and iron; took more multivitamins; had a lower body mass index (BMI); exercised for longer periods of time each day; and consumed more high-fat diary products and less low-fat diary products.

The relationship between these behaviors and reduced risk of infertility was similar for women regardless of age and whether they'd been pregnant in the past, said the Harvard School of Public Health authors of the study, which was published in the Nov. 1 issue of the journal Obstetrics & Gynecology.

"We analyzed what happens if you follow one, two, three, four, or more different factors. What we found was that, as women started following more of these recommendations, their risk of infertility dropped substantially for every one of the dietary and lifestyle strategies undertaken. In fact, we found a sixfold difference in ovulatory infertility risk between women following five or more low-risk dietary and lifestyle habits and those following none," lead author Jorge Chavarro, a research fellow in the school's department of nutrition, said in a prepared statement.

"The key message of this paper is that making the right dietary choices and including the right amount of physical activity in your daily life may make a large difference in your probability of becoming fertile if you are experiencing problems with ovulation," senior author Walter Willett, chair of the department of nutrition, added.

According to the researchers, infertility affects one in six couples, in the U.S. and Europe and ovulatory problems have been identified in up to 30 percent of those cases.

More information

The U.S. National Women's Health Information Center has more about infertility.