Women in the sunniest countries seem to get endometrial cancer less often than those who live far from the equator.

Using a large World Health Organization database, researchers have found lower rates of the cancer, which strikes the lining of the uterus, in populations with a higher exposure to UVB radiation, the ultraviolet light that causes the skin to produce vitamin D.

“There is a mathematical relationship,” said Cedric Garland, a professor of family and preventive medicine at the University of California, San Diego, and a co-author of the study, which appears in the November issue of Preventive Medicine.

The researchers assembled information on endometrial cancer in 107 countries. In both Northern and Southern hemispheres, the higher the latitude, the higher the risk - even after adjusting for many variables. They also found that higher rates of meat eating, per capita health expenditure and the percentage of the population that was overweight were each associated with a higher risk of endometrial cancer.

Though the researchers did not measure vitamin D levels, Garland said, “we believe that vitamin D accounts for the finding, since the geographic distribution corresponds to that of other cancers which have been shown in studies of individuals to be related to levels of vitamin D.”

Stress disorder and asthma A new study has found a link between asthma and post-traumatic stress disorder, though the reasons remain unknown.

The stress disorder, PTSD for short, is common among combat veterans and others who have endured severe trauma. Previous studies have demonstrated a connection between asthma and psychiatric illnesses, but no one knows whether one disorder increases the risk for the other or whether they share a common risk factor, either environmental or genetic.

Researchers used data on 3,065 male twin pairs who had lived together as children and had active duty in the Vietnam War. They adjusted the findings to eliminate the influence of depression, smoking, age, body mass index, exposure to combat and other variables.

One-fourth of men with the most severe symptoms of the stress disorder were more than twice as likely to suffer from asthma as the quarter with the fewest PTSD symptoms.

The association cannot be fully explained by familial or genetic factors; identical twins, who have exactly the same genes, were no more likely to suffer from both illnesses than fraternal twins, who share only half their genes.

The researchers, whose paper appears in the Nov. 15 issue of The American Journal of Respiratory and Critical Care Medicine, are still seeking the explanation.

“It may be a common environmental exposure that increases vulnerability to both disorders,” said Renee Goodwin, the lead author and an assistant professor of epidemiology at the Mailman School of Public Health at Columbia.

‘Dragon’s blood’ may fight ulcer bacterium Researchers have discovered that a plant widely used in traditional Chinese medicine contains compounds that slow the growth of the germ that causes most peptic ulcers.

The chemists, led by Weimin Zhao of the Chinese Academy of Sciences, isolated 22 compounds from the treelike plant, Dracaena cochinchinensis, which gives off a dark-red resinous substance called dragon’s blood. They found two that were effective against the ulcer bacterium, Helicobacter pylori, and eight others that worked as blood thinners.

Their report appears in the October issue of The Journal of Natural Products.

“Many traditional Chinese medicines have been confirmed to possess various beneficial effects,” Zhao said in an e-mail message, “but it is still not easy to understand thoroughly how they work.”

Zhao does not claim that Dracaena, used in China for stomach ailments, fractures and wounds, is a substitute for modern medicine.

Its antibacterial compounds would need to be taken in much higher concentrations than amoxicillin, an antibiotic used for peptic ulcers.

The blood-thinning compounds the researchers found were effective, but not nearly as powerful as, for example, heparin, a common blood thinner.

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