WEDNESDAY, Dec. 12 (HealthDay News) -- Obese people find it harder to fight infections, and a weakened immune response may be to blame, suggests a new study from Boston University researchers.

In experiments with mice infected with the bacteria Porphyromonas gingivalis, obese mice had less ability to battle gum infection than their normal-weight counterparts, according to the report in this week's early online edition of the Proceedings of the National Academy of Sciences.

"For years, we have had difficulty understanding why obese people have difficulty clearing an infection," said lead researcher Dr. Salomon Amar, associate dean for research at the university's School of Dental Medicine.

"Now we understand that dysfunction in some of the mechanisms, as a result of the obesity, explain difficulty in clearing the infection and also the difficulty in wound healing," Amar said.

In the study, Amar's team tied silk threads infected with the bacteria around the molars of obese and normal-weight mice. They then compared the animals' responses to infection, by measuring both the amount of bone loss and the growth of the bacteria around their teeth.

The researchers found that the obese mice had a compromised immune response to the bacteria, which made the animals more susceptible to the infection.

Amar's group also looked at the animals' white blood cells, which are the main line of defense against infection. The white cells of obese mice had lower levels of an important signaling molecule, and some of the genes that fight inflammation were altered, the researchers found.

Why obesity has this effect isn't clear, but the researchers think it may involve a signaling pathway that controls a protein called NF-kB. Alterations in this protein may be caused by constant exposure to food, Amar explained. "At some point, the body doesn't respond properly to infection," he said.

The same mechanism is at work in humans, Amar added. In fact, studies in obese people have shown they are more likely to have gum disease than non-obese people. The disease is caused by bacteria, which causes inflammation and destruction of the bone underlying teeth.

Amar thinks that obese people need to be treated differently to help them fight infections. "We need to be more aggressive in the use of targeted antibiotics in infections among obese people," he said. "Also, we need to boost the immune response."

One expert agreed the finding sheds light on the connection between obesity and infection.

"Very interesting paper," said Dr. Sara G. Grossi, a senior research scientist at the Brody School of Medicine of East Carolina University. "This is a study that needed to be done, with very interesting results and implications for both obesity and periodontal disease -- two diseases that are easier to prevent than to treat."

More information

For more about gum disease, visit the American Academy of Periodontology  .

TUESDAY, Dec. 11 (HealthDay News) -- A quarter-pound hamburger or a small pork chop eaten daily could put you at increased risk for a variety of cancers, U.S. government health researchers report.

The more red meat and processed meat you eat, the greater your risk, the researchers from the National Cancer Institute concluded.

"Red and processed meats have been associated with an elevated risk with colorectal cancer. We investigated whether this association was also evident for cancers at other anatomic sites," explained lead author Amanda Cross, an epidemiologist at the National Cancer Institute (NCI). "This is the largest study to look at the effect of red and processed meat on multiple cancer sites, including rarer cancers, such as laryngeal and liver cancer."

For the study, red meats included beef, pork and lamb. Processed meats included bacon, red-meat sausage, poultry sausage, luncheon meats, cold cuts, ham, regular hot dogs and low-fat hot dogs.

Cross and her team from the National Institutes of Health and the AARP analyzed health data from 500,000 people aged 50 to 71 who participated in the National Institutes of Health-AARP Diet and Health Study beginning in 1995-1996. They followed participants for about eight years, during which time they recorded 53,396 cases of cancer. In addition to meat consumption habits, the participants detailed other lifestyle choices such as smoking and exercise.

The team then grouped people into five categories according to their level of meat consumption.

"The highest category of red meat was those consuming the equivalent of a quarter pound hamburger or a small steak or a pork chop per day," said Cross, who added that the lowest category was equivalent to approximately three thin slices of ham or less per day.

For processed meat, the lowest category of consumption equated to no more than one slice of bacon a day, while the highest consumption category covered four slices a day.

The median consumption of red meat was 31.4 grams per 1,000 calories, which is about two and a half ounces of red meat a day for a person consuming the average 2,000-calorie diet.

Overall, the researchers found elevated risks for colorectal and lung cancer with high consumption of both meat types along with borderline higher risks for advanced prostate cancer. High red meat intake was also associated with increased risk of esophageal and liver and a borderline increased risk for laryngeal cancer. And high processed meat consumption also was associated with borderline increased risk for bladder cancer and myeloma, a kind of bone cancer.

In addition, both red meat and processed meat consumption were associated with increased pancreatic cancer risk in men, but not women.

And the research team noted an unexpected effect of red meat on endometrial cancer: the more red meat women consumed, the less likely they were to suffer from endometrial cancer.

"Our findings for colorectal cancer are consistent with the recommendations from the recently published World Cancer Research Fund and American Institute for Cancer Research to limit consumption of red meats, such as beef, pork and lamb," said Cross. "Our study also suggests that individuals consuming high quantities of red meat may be at an elevated risk for esophageal, liver and lung cancer."

There are several possible routes by which red and processed meats may contribute to cancer, the NCI researchers said. Meats are a source of saturated fat and iron, both of which have been linked to cancer, and also the source of several compounds that are known to affect cell development, they added.

Cooking at high temperatures might also contribute to cancer risk, Cross added.

"Heterocyclic amines and polycyclic aromatic hydrocarbons are formed when meats are cooked well-done by high temperature cooking methods, such as barbecuing," she said.

The study, published in the December 2007 issue of the online journal PLoS Medicine, brought a mixed response from experts in the field.

"This adds to the body of knowledge that supports recommendations that to reduce the risk of colon cancer, you should reduce your consumption of red and processed meats," said Colleen Doyle, director of nutrition and physical activity for the American Cancer Society. "It also adds to the smaller amount of research tying red and processed meats to other types of cancer risk. The American Cancer Society recommends reducing red and processed meat consumption to reduce the risk of prostate cancer."

"We really see this study that it further illustrates the complexity and challenges of understanding research related to diet and cancer. They also could have said red meat is protective of endometrial cancer. The challenges of looking at diet and cancer are just vast," said Mary K. Young, vice president for nutrition with the National Cattlemen's Beef Association. She noted that the researchers did not ask how food was prepared, which she said could have affected the health outcomes.

Doyle and Young, both dietitians, agreed that diet can play a critical role in health.

"One of the most important things people can do to lower their risk of chronic disease, including cancer, is maintain a healthy weight," added Young, who recommended that people follow national dietary guidelines, watch their serving sizes and stay physically active.

People worrying about cancer and diet should take a balanced approach, said Doyle. " No one food is going to put our cancer risk over the top. If you are someone who eats steak or pork or lamb or salami or hot dogs, etc., on a regular basis and/or in large portion sizes, I would probably suggest you look for healthier protein sources to include in your diet," she added. The American Cancer Society recommends that people eat lots of fruits, vegetables and whole grains with some lean proteins to prevent cancer.

Research released last summer in the e Journal of the National Cancer Institute suggested that choline, found in many red meat and dairy products, may contribute to the growth of polyps that lead to colon cancer.

And another study, released in the Aug. 17 Journal of the American Medical Association, showed that colon cancer patients who eat a diet rich in fruits, vegetables, poultry and fish can significantly lower the risk of their cancer returning. In contrast, those patients whose self-reported diet included high intakes of meat, fat, refined grains and dessert were more than three times more likely to see their colon cancer return.

"If I were a cancer survivor," Doyle said, the new research "would make me stand up and take notice."

More information

To learn more about how diet and physical activity choices can help prevent cancer visit the American Cancer Society's Food and Fitness guide  .

MONDAY, Dec. 10 (HealthDay News) -- Being in good physical form appears to protect middle-aged and older men and women from stroke, a new British study suggests.

The finding highlights an apparent association -- rather than a direct cause-and-effect -- between the physical ability to function well and a reduced risk for stroke.

After sifting through thousands of quality-of-life reports provided by patients themselves, the research team found that those functioning at the higher end of the physical capacity spectrum appear to have half the risk for stroke as their poorest functioning compatriots, independent of other risk factors.

"We were surprised at the magnitude of the relationship, as this is comparable to established stroke risk factors such as smoking," noted study author Dr. Phyo Kyaw Myint, who works with the Clinical Gerontology Unit at Addenbrooke's University Hospital in Cambridge.

The findings are published in the Dec. 11 issue of Neurology.

Myint and his colleagues uncovered an apparent stroke-physical function connection by analyzing data concerning more than 13,600 British men and women between the ages of 40 and 79.

All the participants first completed a health examination and questionnaire between 1993 and 1997. At that time, patient blood pressure, body-mass index, respiratory capacity, and cholesterol levels were assessed. Researchers also noted any history of diabetes, smoking and alcohol consumption.

None of the patients had experienced any incidence of cancer, stroke or heart attack before their initial exam.

Eighteen months after the initial exam, patients completed a follow-up questionnaire by mail, in which patients were asked to indicate their degree of physical and social functioning; their mental health status; any physical and/or emotional limitations on carrying out routines; energy levels; experiences of pain; and self-perceptions regarding their overall health.

All participants were followed until 2005, by which point 244 strokes were recorded.

The researchers found that those men and women who reported better physical function had a considerably lower risk for stroke.

After adjusting for all other observed characteristics -- including gender and age -- Myint and his team found that patients in the top quarter of physical function capacity had half the risk of stroke when compared with patients in the lowest quarter of physical function.

The authors concluded that poor physical function could indicate a high risk for stroke, thereby highlighting a specific segment of the general population that could derive particular benefit from some form of intervention.

Myint stressed, however, that to date his team has simply conducted a hands-off review of patient self-reports regarding their physical capacity and lined those reports up against stroke incidence records. At no time were patients assessed for their ability to follow a prescribed physical activity routine of varying intensities and durations.

He cautioned against leaping to the notion that greater physical function or activity directly causes a drop in the risk for stroke.

"We don't know whether physical function per se is causally related to stroke or simply a good marker for other factors that influence stroke risk," Myint noted. "These findings need confirmation from other studies. However, there is already a substantial body of evidence for public health recommendations to increase physical activity."

In the meantime, Alice H. Lichtenstein, director of the Cardiovascular Nutrition Lab at Tufts University in Boston, said that people should not sit idly by while investigators continue to unravel the complex web of factors related to stroke risk.

"This study does not show causation, but clearly, individuals who follow current guidelines for decreasing risk for stroke and general cardiovascular risk -- including keeping physically active -- have better outcomes," she said. "So, in terms of both physical function and activity, what people need to try to do is go from where they are to more."

"For some people, doing more may literally mean just walking around the block once, or picking up the pace, or adding extra time moving," said Lichtenstein. "For others, it can even be something like doing the housecleaning. And it can be cumulative: 10 minutes at one point, 10 minutes at another. Because although we'd like everyone to set aside special time just for physical activity every day, we know that for a lot of people, it's just not going to happen. So, any increase is going in the right direction, and that should be the goal."

This week, the American Society for Nutrition is poised to issue a new set of national recommendations regarding both physical activity and nutrition.

The recommendations are described as "comprehensive, scientific guidelines on physical activity for all Americans." According to the U.S. Department of Health and Human Services, the guidelines will gather together the latest knowledge on both healthy eating and regular physical activity.

More information

To learn about stroke risk, visit the American Heart Association  .

MONDAY, Nov. 19 (HealthDay News) -- U.S. researchers say they've uncovered new clues on how embryonic cells regulate levels of retinoic acid, a derivative of vitamin A.

Retinoic acid plays a vital role in embryo development, acting as a signal between cells to control development of the brain, limbs and many other tissues. Human embryos that get too much or too little retinoic acid may develop birth defects, noted a team from the University of California, Irvine.

When humans consume vitamin A -- found in many foods, including carrots, broccoli and sweet potatoes -- the body converts it into retinoic acid.

"If you don't get enough vitamin A in your diet -- or if you get too much -- your body compensates for that. Our study helps explain how this regulation occurs," Thomas Schilling, associate professor of developmental and cell biology at UC Irvine, said in a prepared statement.

The UC Irvine team examined retinoic acid in zebrafish embryos, which are often used in genetic studies as models for human development. They found that if levels of retinoic acid become too high, an enzyme called cyp26a1 degrades the excess retinoic acid in order to restore normal levels. If levels are too low, proteins called fibroblast growth factors (FGFs) slow retinoic acid degradation.

"Those two things work together to keep the whole system adjusted to the right level. Retinoic acid induces its own degradation, and FGFs, also present in the embryo, have the opposite effect by inhibiting retinoic acid degradation," Schilling said.

The study is published in the Nov. 20 issue of the journal Public Library of Science Biology.

More information

MedlinePlus has more about vitamin A.