Higher birthweights are linked to increased blood pressure in African-American but not white children, reports a study in the September Journal of the American Society of Nephrology.

The findings raise new questions about a recent theory that infants with lower birthweights are at increased risk of blood pressure and other health problems later in life. They also suggest that, if blood pressure is indeed “programmed” at birth, the process may differ by race.

Led by Dr. Anusha H. Hemachandra of The Johns Hopkins University School of Medicine, Baltimore, the researchers analyzed data on nearly 30,000 black and white children within the United States, from birth through age 7. Previous studies of the link between birthweight and blood pressure have been performed mainly in Caucasian populations, Dr. Hemachandra notes. “The lack of data on African-Americans prompted us to study a large biracial American cohort to examine the association between birthweight and blood pressure at age 7 years in both black and white populations.”

The results showed a direct relationship between birthweight and blood pressure - but only in black children and in a direction opposite from that expected. “For African-American babies, the heavier they were at birth, the higher their risk for high blood pressure in childhood,” says Dr. Hemachandra. “This is in contrast to the white children in the study, who had no significant relationship between birth weight and blood pressure.”

For African-American children, the relationship between birthweight and blood pressure remained significant after adjustment for factors related to the mother. Maternal poverty and lower education were strong risk factors for high blood pressure in children.

As an indicator of restricted growth in the womb, low birth weight has been linked to an increased risk of various chronic diseases in adulthood. “First publicized by Dr. David Barker in Great Britain, the ‘fetal programming’ or ‘fetal origins of adult disease’ hypothesis suggests that stresses faced by the fetus in the womb may alter its physiology permanently,” explains Dr. Hemachandra. “These adaptations help the fetus survive the stress in utero, but are not helpful and may even be dangerous in postnatal life, leading to an increased risk for chronic diseases such cardiovascular disease and type II diabetes.”

Under this “fetal programming” theory, the high rates of hypertension in the African-American community might be explained by an increased prevalence of low-birth-weight infants. However, the new results suggest that high-birth-weight African-American babies are the ones at increased risk for high blood pressure later in life, whereas white infants show no relationship between birth weight and blood pressure. This racial difference suggests that, if hypertension risk is “programmed” during the fetal period, the risk may be “race-specific” and at least partly affected by genetics.

“Our study adds to the growing body of evidence suggesting that public health initiatives to prevent chronic diseases such as hypertension may need to begin as early as the prenatal and early childhood period,” Dr. Hemachandra concludes. “Exploring racial disparities in the developmental origins of health and disease is a critical step toward understanding the mechanisms of fetal programming and eventually developing interventions against chronic disease.”

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American Society of Nephrology (ASN)