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Study: Boys born thin but heavy as teens have greater risk for high blood pressure

CHAPEL HILL -- Boys who are born lean but add a lot of weight between ages 8 and 15 face an increased risk of high blood pressure, said researchers from the University of North Carolina at Chapel Hill and the Institute of Child Health in London.

A report on the study, funded by the National Institute of Child Health and Human Development, appears in Tuesday’s (Feb. 11) edition of Hypertension: Journal of the American Heart Association.

"The boys who were thinnest at birth and who gained the most weight during childhood and adolescence were the ones who had the greatest risk of high blood pressure," said lead author Dr. Linda Adair, professor of nutrition at UNC’s schools of public health and medicine.

Those who experienced more rapid growth in the first two years of life did not demonstrate an increased risk of having elevated blood pressure in adolescence, however, regardless of whether they were thin at birth.

"Faster growth in infancy did not represent a risk for increased blood pressure in adolescence for either sex," Adair said. "This period of weight gain may even be slightly protective against high blood pressure later. This is an important finding because pediatricians want to see improved growth in babies born small."

In addition, Adair and study co-author, Dr. Tim Cole, found a similar increase in blood pressure risk among girls who gained significant weight in childhood and adolescence. Unlike the boys, however, there was no relationship between this risk and thinness at birth.

Cole is a professor of medical statistics at the Centre for Paediatric Epidemiology and Biostatistics, part of the Institute of Child Health in London.

The researchers used data collected from the Cebu Longitudinal Health and Nutrition Survey, which enrolled pregnant women and followed their offspring through age 14 to 16 years. More than 3,000 infants from the greater Cebu, Phillipines, area were assessed regularly while enrolled.

"The value of the Cebu study is that we have repeated measurements of these kids from birth," Adair said. "We know about their growth, nutrition, infectious diseases and physical activity, all of which can affect risk factors."

Using the Cebu data, Adair and Cole found male birth weight significantly associated with high blood pressure only after controlling for birth length, suggesting that it is thinness rather than weight that matters.

The magnitude of the effect was substantial, Adair said. Among boys in the top third for childhood weight gain after age 8, those who were thin at birth had a predicted probability of high blood pressure that was nearly twice those who were relatively heavy at birth.

Conversely, larger weight and length gains that occurred in infancy – rather than later – reduced the odds of high blood pressure in adolescence.

"Using more detailed information from birth to adolescence allowed us to pinpoint the time period when growth matters most," Adair said. "It turns out that growth during infancy, in this study at least, was not a risk factor, but more rapid weight gain later on was."

As a result of their findings, Adair and Cole said pregnant women need to receive adequate nutrition and health care to avoid fetal growth retardation. Early prevention also should include the promotion of breastfeeding and healthy, proportional child growth, the researchers said.

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Note: Adair can be reached at (919) 966-4449 or linda_adair@unc.edu. Cole can be reached at (011) 020 7905 2362 or Tim.Cole@ich.ucl.ac.uk.

UNC School of Public Health contact: Lisa Katz, (919) 966-7467 or lisa_katz@unc.edu
UNC News Services contact: Deb Saine, (919) 962-8415