Report Shows Drop in Baby Boys

The gap between the number of boys and girls being born in the United States has narrowed, according to a new government report that confirms earlier studies.

Historically, far more boys than girls are born each year. In the most comprehensive assessment of the trend to date, researchers at the Centers for Disease Control and Prevention analyzed all birth records in the United States between 1940 and 2002.

While far more boys than girls were born every year -- nearly 92,000 more on average -- the researchers found that there were two distinct periods when the gap narrowed significantly: between 1942 and 1959 and then again between 1971 and 2002.

The researchers noted that the drop was relatively small. The highest ratio was 1,059 male births per 1,000 females in 1946; the lowest was 1,046 males per 1,000 females in 1991. Nonetheless, the trend could have a significant impact on the nation's overall demographics over time, they said.

The reason for the drop is the subject of intense debate. Some scientists and environmental activists are concerned that a pollutant may be to blame, but other researchers suspect social factors, such as an increase in the number of older women giving birth.

"There are lots of theories," said T.J. Mathews, a demographer at the National Center for Health Statistics.

-- Rob Stein

Study: Friends Help Longevity

Having a broad network of good friends increases the likelihood that older people will live longer. Having close family ties does not.

A 10-year study that monitored the personal and telephone contacts of almost 1,500 people in Adelaide, Australia, came to that surprising conclusion. The result was strengthened by the finding that the survival effect was greatest for people with the broadest and deepest network of friends, and weakest for those with the fewest friends and close confidants.

The study was part of a broad look at the health and well-being of people 70 and older, and took into account a range of factors including health, lifestyle and economic status. Earlier studies had found that social contact of all kinds increases longevity, but this research looked at which kinds of contact had the most effect.

Researchers examined three categories of social activity -- with friends, with confidants not necessarily close friends, and with family. They found that 10 years after the study began, those who reported having many close friends had lived significantly longer than average, those with confidants somewhat longer, and those whose network revolved around children and relatives not longer at all.

The authors, from Flinders University in Australia, proposed that friends may increase survival by encouraging people to engage in healthier behavior. They also wrote that "friends can have effects on depression, self-efficacy, self-esteem, coping and morale, or a sense of personal control." While family contact can have some of those effects, they wrote, the fact that people can't choose family members but do choose their friends appears to make a significant difference.

The study, funded by the South Australian Health Commission and the U.S. National Institute on Aging, appears in the Journal of Epidemiology and Community Health.

-- Marc Kaufman

Researchers Grow Blood Vessels

Behind the lines where battle is being waged over the use of embryonic stem cells for research, scientists are making advances in growing human spare parts from far less controversial starting materials.

In the current edition of the Lancet, a team led by Laura E. Niklason of the departments of anesthesia, surgery and biomedical engineering at Duke University describes its success in growing human blood vessels.

Bypass surgery is performed about 400,000 times a year in the United States, with patients contributing their own veins and arteries used to route blood around blocked coronary arteries. Sometimes, though, people requiring second procedures don't have vessels left to donate. It would be useful if they could "custom-grow" new ones for surgical use.

The main constituents of blood vessels are smooth-muscle cells, which form the wall, and endothelial cells, which form the lining. These two types of cells can be extracted from veins and grown in tissue culture. The problem is that cells taken from older people have limited capacity to divide. They don't grow for a long enough time to make useful blood vessels.

Niklason and her colleagues addressed this problem by increasing the "replicative capacity" of adult blood-vessel cells. Their strategy was to stop the erosion of telomeres, the tail-like structures on the end of chromosomes that get shorter with each cell division. When there is no telomere left, the cell can't divide further.

The Duke team took veins from four men whose ages ranged from 47 to 74. They then isolated the two types of cells and treated them with genes that stopped the telomeres from shortening. Then they grew artificial vessels with the cells over the course of seven weeks, using silicone tubing as a scaffold.

Cells from men 47 and 55 years old whose telomeres weren't altered grew flimsy vessels that burst easily, compared with ones grown from cells with doctored telomeres. Cells from men 67 and 74 years old didn't grow vessels at all.

While the engineered vessels still aren't good enough to take to the operating theater, the strategy may be a substantial advance in bioengineering.

-- David Brown