Sports such as soccer -- with the combination of weight-bearing exercise and repetitive, "impact-loading" from jumping and running -- have been shown to build bone mineral density in adolescent girls better than some other activities.

Building bone density during the teen years is considered crucial for healthy bone development, helping to ward off osteoporosis, the disease that causes bones to become brittle and break later on in life. Peak bone mass is typically achieved by age 30, according to the National Osteoporosis Foundation.

"It's those years of adolescence, and early teens to late 20s, that are most important" for bone building," said James W. Bellew, an associate professor of physical therapy at Louisiana State University Health Science Center-Shreveport.

Bellew and his colleagues compared the effects of soccer, weight-lifting and swimming on the bone mineral density of teen and pre-teen girls, ages 10 to 17. The groups included 29 swimmers, 16 soccer players and 19 weightlifters.

Soccer players had the best bone density, followed by the weight-lifters and then the swimmers. Bellew's team compared the groups' average bone mineral density to what is considered the norm for a 25-year-old woman.

Soccer players' bone density was significantly greater than the norm, and the weight-lifting group was equal to the norm. The swimmers were lower than the norm. Still, that's not cause for alarm, he said, because the girls were still in their teens and have time to accrue bone density.

Soccer and other "impact" sports expose the body to repeated impact, and that activity is thought helpful to bone health. "Basketball and volleyball may very well do the same" as soccer in building bone, he said. Jogging and tennis may also be good, he added.

The study results, published in the journal Pediatric Physical Therapy, don't surprise Susan Randall, senior director of education at the National Osteoporosis Foundation. "Swimming is not a weight-bearing exercise," she said. "Soccer increases the loading on the bone which actually stimulates bone production."

Bellew isn't discouraging those who love swimming to give up the sport. "The odds are the swimmers' density [in the study] will be fine, because they are active, but our data suggest they aren't accruing as much bone as those who do weight-bearing exercise."

"If your primary objective is to increase bone mass, swimming is not the best," he said. "But in terms of weight maintenance, it's good."

Besides exercise, Bellew suggests teens can boost their bone health by reducing their soda intake and increasing their milk consumption. "Genetics is probably the largest factor," he added, so those with a family history of osteoporosis may want to pay even more attention to bone-building exercise.

Randall agreed that families should pay even closer attention to their children if a parent or grandparent suffers from low bone density. And parents can emphasize a healthy diet for their sons as well as daughters. While men are less likely than women to suffer osteoporosis, they still need to build bone, she said.

One of the first foods teen girls often abandon are dairy products, Randall said, because they perceive them as fattening. Parents should be sure their children get the recommended 1,300 milligrams of calcium a day. That's roughly the amount of calcium in four glasses of milk. And the milk can be low-fat, she said.

More information

To learn more about bone health, visit the National Osteoporosis Foundation.

Here are signs that your baby may be in pain, courtesy of the University of Michigan Health System:

• Unusual crying: If the cry is in a different pitch than usual, if the crying lasts longer, or if the baby is crying more forcefully.
• Facial features: If the baby is squeezing the eyes shut, furrowing the brows, or has deep lines or wrinkles around the nose.
• A stiffness or tenseness to the body: If the baby has the arms and legs stretched out, or squeezes them in close. Some babies may seem unusually limp or quiet when in pain.
• Irritability: If you can't soothe the infant by the usual methods. Also, the infant may be fussy, restless and unwilling to eat or sleep

THURSDAY, May 1 (HealthDay News) -- Not having money hurts. Physically.

Lower-income Americans experience pain much more frequently than those making more money, according to a study that had nearly 4,000 people keep a diary in which they scored their feelings of pain on a scale of 0 to 6 for randomly selected 15-minute intervals.

People with household incomes below $30,000 a year reported moderate to severe pain 20 percent of the time. Those making more than $100,000 a year said they experienced pain less than 8 percent of the time.

"The arrows point in both directions," said study co-author Alan Kreuger, a professor of economics at Princeton University, explaining the findings reported in the May 3 issue of The Lancet. "First, people with lower skills tend to do more physically demanding labor, and that leads to pain. Secondly, people who have a lot of pain in their lives find it hard to work."

Education also affected pain results. People with less than a high school degree reported twice the average pain rating through the day as those with college degrees, the study found.

The pain study was an extension of work done in association with Arthur Stone, a professor of psychiatry and behavioral science at Stony Brook University in New York, Kreuger said. "We had been doing work on how people used their time and how they felt about it, and decided to add questions about pain to this national survey," he said.

The link between pain and lower income and socioeconomic status wasn't necessarily a surprise, Krueger said. "We sort of expected to find that," he said. "But there was a much stronger relationship than I expected."

The nature of someone's work had a strong influence on the experience of pain. Blue-collar workers reported higher rates of pain and more severe pain than those with desk jobs. And the 13 percent of people with work-related disabilities accounted for 44 percent of the time Americans spent in moderate to severe pain, the study found.

Some other survey findings were predictable. People were more likely to feel pain while alone, and those with pain spent almost 25 percent of their time watching television, compared to 16 percent for those experiencing less discomfort.

And people felt more pain as they grew older, with the average pain rating increasing with the years. But there was a surprising temporary plateau between the ages of 45 and 75, after which pain increased, the study found.

The fact that the pain imbalance persists after the working years indicates that "more attention should be paid to economics and health-care services," said Juha H.O. Turunen, a professor of social pharmacy at the University of Kuopio in Finland, who wrote an accompanying editorial in the journal.

"Studies over the years have shown that people with less education and low income suffer from more pain," Turunen said. "Their work environment is different, and they are not as interested in taking care of their health. Life habits are associated with economic status."

One notable finding of the survey was that people responsible for the care of others reported very high pain scores, Turunen said. "Attention should be paid by society," he said. But, he added, he'd avoid making recommendations about the United States because of his unfamiliarity with America's health-care system.

More information

If you really want to read more about pain, consult the U.S. National Library of Medicine.

Researchers from Vanderbilt University Medical Center in Nashville, Tenn., looked at 235 people, average age 80.1 years, who were monitored for an average of 6.8 nights. The team used wrist actigraphy to gather data on the participants' sleep patterns and circadian rhythms. The volunteers also kept sleep diaries.

The results showed that naps of at least five minutes were recorded in sleep diaries by 75.7 percent of the participants. Napping was most likely to occur in those with higher levels of nighttime sleep fragmentation, respiratory symptoms, diabetes and pain.

Self-reported diabetes was associated with a 43 percent longer nap duration, while self-reported pain was associated with a 27.5 percent shorter nap duration. Each hour of previous night's sleep time was associated with a 4.1 percent longer sleep time the next night (nap night), and each hour of napping (the next day) was associated with 10.2 percent less sleep on the night of the nap.

"Our study is important both clinically and for future research. It points out the need for health care providers to discuss nighttime sleep and daytime napping with older individuals," study author Suzanne E. Goldman said in a prepared statement.

The study "also points out the need to identify the causes of disturbed nighttime sleep in order to determine appropriate treatment. Our study suggests that older adults nap because of health problems and disrupted sleep at night. Thus the napping may reflect needed sleep," Goldman said.

The study was published in the May 1 issue of Sleep.

Lack of sleep can lead to a number of problems in older adults, including depressed mood, attention and memory problems, excessive daytime sleepiness, more nighttime falls, and increased use of sleep medications.

Research has also linked lack of sleep with increased risk of serious health problems such as obesity, cardiovascular disease and diabetes.

More information

The U.S. National Sleep Foundation has more about aging and sleep.

While not a predictor of individual risk for osteoporosis, this finding could lead to new therapies to combat the disease, they noted.

"When we look at a screening of genes for osteoporosis and low-impact fractures, we find five loci in the genome, and a couple of them fall into very well-known areas associated with the formation of bone," said researcher Dr. Kari Stefansson, founder and CEO of deCODE Genetics in Reykjavik, Iceland. His team's report was published Tuesday online as an early release from the New England Journal of Medicine.

Osteoporosis, however, involves many genes, not just the five areas identified in this study, Stefansson noted. "Osteoporosis is a very complex phenomenon," he said.

Stefansson was clear that these findings are not something that can be used in diagnosing osteoporosis. "It is a very exciting insight into the biology," he said. "We are beginning to understand osteoporosis."

One of the genes, the researchers identified it as the RANKL gene, is a target of new drugs in clinical trials being tested for osteoporosis, Stefansson said.

In the study, Stefansson and colleagues analyzed genes from 5,061 Icelanders. The researchers looked at those associated with bone mineral density.

Stefansson's team found a significant association with bone mineral at five gene regions. These regions are close to or included in genes that have previously been shown to be associated with bone and the development of osteoporosis.

In addition to RANKL, the other genes are the estrogen receptor 1 gene, the osteoporosis gene, and a gene region, including 40 genes called ZBTB40. In addition, the gene region identified as 6p21 is also involved in bone mineral density, the researchers reported.

Identifying these genes is not going to have an immediate impact on osteoporosis diagnosis or treatment, Stefansson said. However, in the near future, these genes may be drug targets for treating osteoporosis, he added.

"These genes do not have a diagnostic value, because their impact on individuals is rather small," Stefansson said. "Although these genes explain a very large part of the disease in our society, because just one loci we found explains 17 percent of all cases of osteoporosis in the population."

One expert thinks that these genes are only a small part of the story of osteoporosis.

"Taken together, these genes only account for 3 percent of variation in bone density," said Dr. J. Chris Gallagher, a professor of medicine and endocrinology at Creighton University School of Medicine in Omaha, Neb., and a board member of the North American Menopause Society.

Gallagher noted that a couple of these genes, including the osteoporosis gene and RANKL, are already being looked at as targets for drug therapy.

Moreover, these genes are not strong predictors of osteoporosis, Gallagher said. "It means there are many more things involved that contribute to the overall picture," he said.

In a second study, published in the April 29 early online edition of The Lancet, an international team of researchers reported identifying two genetic variants that, when present together, significantly increase the risk of osteoporosis and bone fractures.

These variants are found in 22 percent of the people studied, perhaps making them targets for screening, the researchers noted. Having both of these variants increases the risk for osteoporosis by 20 percent and the risk for osteoporosis-related fractures by 30 percent, the researchers reported.

The researchers concluded that these gene variants "could be used in the future, in addition to traditional risk factors, to better identify populations who are at high risk for osteoporotic fractures."

More information

For more about osteoporosis, visit the U.S. National Institute of Arthritis and Musculoskeletal and Skin Diseases.