An individual’s life expectancy is influenced by their weight at birth, with smaller babies living, on average, fewer years than their heavier peers, new research by Yale University’s Center for Pediatric, Perinatal and Environmental Epidemiology (CPPEE) suggests.
Small body size at birth has been associated with increased risk of heart disease and stroke, while high birth weight has been linked with increased risk of obesity, diabetes and some adult cancers. But the net effect of birth weight on adult mortality has only been assessed in individual studies, often with conflicting results, said Kari Risnes, M.D., of the Norwegian University of Science and Technology and a visiting researcher at CPPEE.
To learn how body size at birth influences adult mortality, the researchers, led by Michael B. Bracken, Ph.D., the Susan Dwight Bliss Professor of Epidemiology at the Yale School of Public Health, conducted a systematic review and meta-analysis of previously published studies on the topic. Their analyses comprised nearly 40,000 deaths, including 11,400 from cardiovascular causes and 8,300 from cancer.
The researchers found that lower birth weight increased the risk of adult mortality from all of the causes considered. Individuals with a birth weight of less than 3,000 grams (or about 6.61 pounds) had a 13 percent increased overall mortality risk compared to individuals born with birth weight between 3,000 to 4,000 grams.
For cardiovascular mortality, a 1,000 gram (about 2.2 pounds) increase in birth weight corresponded to a 12 percent decreased risk. For death from cancer, the results differed for men and women. While birth weight did not predict cancer mortality in women, a 1,000 gram increase in birth weight increased the risk of cancer death for men by 13 percent. Although most of the included studies adjusted for indicators of socioeconomic status, which could affect both birth weight and mortality risk, possible effects of pre-term birth, smoking and maternal factors such as diabetes and overweight could not be ruled out.
“The study confirms that individuals born small suffer from adverse long-term consequences, especially on cardiovascular health. The leading explanation has been that under-nutrition in fetal life may cause adaptations in the fetus that increase disease susceptibility in adult life, especially if nutrition is abundant after birth,” said Risnes.
A meta-analysis combines data from separate but related studies to evaluate the pooled results. The research team considered all cohort studies that reported whether size at birth is associated with adult mortality. Included studies had to be published in peer-reviewed journals from 1966 through October 2010. After eliminating studies that failed to meet quality criteria for inclusion, they whittled their list down to 22 studies that reported on the association between birth size and adult mortality from one or more of the following causes of death: all causes combined, cardiovascular or all cancers deaths.
The study was a collaboration between the CPPEE at Yale University, the Norwegian University of Science and Technology, and co-investigators from eight countries. The results are published in the International Journal of Epidemiology.