U.S. researchers have begun a groundbreaking trial to test the potential of umbilical cord blood transplants, a kind of stem cell therapy, to treat and possibly reverse hearing loss in infants.

The phase I trial follows promising studies on mice showing that such transplants were able to rebuild the structures of the inner ear, and some anecdotal evidence from humans, sparking hope of a cure for some forms of deafness.

A lead poisoning epidemic in Nigeria's north that has killed 400 children and affected thousands is the worst in modern history, but cleanup has not even begun in many areas, Human Rights Watch said Tuesday.

"Thousands of children in northern Nigeria need immediate medical treatment and dozens of villages remain contaminated two years into the worst lead poisoning epidemic in modern history," the US-based group said in a statement.

Men who smoke experience greater mental declines over time than men who never smoked, but the same link does not appear among women, said a British study published in the United States on Monday.

The research suggested that the effects of long-term cigarette smoking show up terms of memory loss, inability to connect past experience with actions in the present, and a drop in overall cognition skills.

A drug tipped for widespread use to prevent breast cancer in post-menopausal women also accelerates loss of bone density, thus potentially boosting the risk of fractures, a study published on Tuesday said.

Exemestane -- brand name Aromasin -- is part of a drug class called aromatase inhibitors, which lower levels of the estrogen that some breast cancers need in order to grow.

Infants outgrowing a liquid diet who give themselves finger food rather than being spoon-fed puree are likelier to eat healthily and avoid getting fat during weaning, reports a study released Tuesday.

Researchers found that the technique, known as "baby-led weaning," led to a child expressing a clear preference for pasta, rice and other carbohydrates over sweets, thus helping to cement a foundation for eating the right foods.

Texting while driving, speeding and back-seat hanky-panky aren't all that parents need to worry about when their kids are in cars: Add secondhand smoke to the list.

In the first national estimate of its kind, a report from government researchers says more than 1 in 5 high school students and middle schoolers ride in cars while others are smoking.

A proposal to use new diagnostic criteria for autism has roiled the U.S. medical community, with many experts concerned that the move could exclude children affected by some forms of the disorder.

The American Psychiatric Association recommended last month that a new category called "autism spectrum disorder" be established to incorporate several forms of autism which were previously considered separately.

Germany, holding up better than its eurozone partners in the current debt crisis, is battling the increasingly widespread phenomenon of "burnout" which it says is costing its economy billions of euros (dollars) each year.

According to data compiled by the economic institute of the public-sector health insurer AOK last year, psychological illness is on the rise among Germany's workforce.

A nine-year-old girl is making what doctors described as a remarkable recovery Sunday, days after surgeons transplanted six of her organs in a groundbreaking medical procedure.

The surgery performed last Tuesday on young Alannah Shevenell, sought to remove an aggressive cancerous growth festering since 2008, and that had attacked her stomach, liver, pancreas, esophagus, small intestine and spleen.

U.S. health authorities on Friday urged all boys age 11-12 to get a routine vaccination against the most common sexually transmitted disease, human papillomavirus, or HPV.

Other changes as part of an annual update to U.S. immunization schedules included a recommended hepatitis B vaccine to the protect the livers of adults up to age 60 who have diabetes and a vaccine against whooping cough for pregnant women.