April 2, 2009 -- Low-birth-weight babies have been shown in numerous studies to have an elevated risk for heart disease in adulthood, and now a new study may help explain why.
Researchers from England's University of Manchester report that young adults in their study who were small at birth and during infancy had higher white blood cell counts, indicative of inflammation, than young adults born at a normal weight.
Earlier studies suggest that as early as age 6, children born small for their gestational age have more white blood cells than children born at a normal weight.
Now the new research suggests that the association persists into early adulthood and probably beyond, study researcher Dexter Canoy, MD, PhD, tells WebMD.
"Our findings indicate that the link between poor growth early in life and these adult chronic diseases may involve inflammation as a common underlying factor," Canoy says.
Smallest Babies Had Most Inflammation
Canoy and colleagues were able to follow 5,619 residents of northern Finland from birth to age 31, using data from a national study of babies born in 1966.
They compared weight at birth and at 1 year of age to white blood cell counts at age 31; the smallest babies and those whose early growth was slowest had the highest white blood cell counts.
The researchers will continue to follow the people in the study to find out if they actually end up having more heart disease, diabetes, or other diseases that have been linked to both low birth weight and inflammation.
"These diseases typically occur much later in life, so we hope to follow these subjects for decades," he says.
The study is published in the Journal of Clinical Endocrinology & Metabolism.
'Thrifty Phenotype' Hypothesis
The observation that poor fetal growth contributes to chronic disease in adulthood was first proposed in the 1980s by U.K. researcher David J. Barker of the University of Southampton.
Commonly known as the "thrifty phenotype" hypothesis, the thinking is that metabolic adaptations made in response to nutritional deprivation become permanently programmed, leading to an increased risk for many chronic diseases in adulthood.
Dozens of large-scale studies conducted in the U.K., the U.S. and elsewhere have shown a link between impaired fetal growth and heart disease, stroke, and diabetes in adulthood, researcher Daniel T. Lackland, DrPH, tells WebMD.
Lackland, who has collaborated with Barker on several studies examining birth weight and chronic disease, says the study by Canoy and colleagues makes a compelling case that inflammation plays an important role in the process. Lackland is a professor of epidemiology at the Medical University of South Carolina in Charleston.
Babies born weighing less than 5.5 pounds are generally considered low birth weight, and those weighing less that 3.3 pounds are considered very low birth weight.
"The studies have consistently shown that the smaller a baby is at birth, the greater the risk," Lackland says. "That doesn't mean that someone who is born small is definitely going to have high blood pressure or will have a stroke or heart attack. But it does mean that their risk for these events may be higher."