ZT Birth weight may hint at lifespan

Birth weight may hint at lifespan, study says
Sat, Mar 22, 2008 (Reuters Health) — Low birth weight confers an increased risk of dying early as an adult, but people born extra-heavy are at greater risk too, according to the largest study to date to look at birth weight and mortality from any cause.

"More infants than ever before are being born with these high birth weights," Dr. Jennifer Baker of the Centre for Health and Society in Copenhagen, who led the study, told Reuters Health. "Further research is really needed to determine what may happen to these children when they grow up."

Past research has linked small size at birth to heart disease and diabetes risk, while people who were very large babies seem to have a heightened risk of obesity and cancer. But studies of birth rate and mortality risk have had mixed results, and no one study has looked at more than 29 birth years in a row.

To further investigate the relationship, Baker and her team looked at 216,464 men and women born during a span of 44 years (1936-1979). They compared birth weight with risk of death from any cause from age 25 to 68 (or up to 2004, for younger individuals).

They found that men and women who weighed between 2,000 and 2,750 grams at birth (4.4 to 6.0 pounds) were at 17 percent greater risk of death during the study's follow-up period than people with birth weights between 3,251 and 3,750 g (7.1 to 8.3 pounds).

Weighing in at 4,251 to 5,500 grams (9.4 to 12.1 pounds) at birth increased deaths during the follow-up period by 7 percent.

When the researchers looked at cause of death separately, they found that deaths from cardiovascular disease followed a similar "U-shaped" pattern. However, the risk of dying from cancer was lowest for the smallest birth weight individuals and rose steadily as birth weight increased.

Both low- and high-birth weight infants tend to develop low blood sugar, while very small infants may also have high blood sugar, the researchers note. "Sustained exposure to either state can permanently impair brain development," they add. "We speculate that this could lead to cognitive deficits and impairments in the regulation of body processes, which might contribute to the elevated risks of mortality observed at both ends of the birth weight spectrum."

In a commentary published with the study in the journal Epidemiology, Dr. Olga Basso of the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina, writes: "Birth weight may be forever. We can hope that it will not take that long to understand why."