Lifestyle factors that increase the risk of heart disease in adults begin to take hold in childhood

Oct 11 2004

Lifestyle factors that increase the risk of heart disease in adults begin to take hold in childhood, and possibly even before birth, according to two studies reported in Circulation: Journal of the American Heart Association.

In one study, Boston researchers found that about two-thirds of 1,960 adolescents studied had at least one risk factor for heart disease, and almost 10 percent had a cluster of factors known as metabolic syndrome.

In the other study, British and Australian investigators looked at parental and early-life characteristics and their association with blood pressure in 5-year-old offspring. The children of women who smoked during pregnancy had higher blood pressure compared to children of nonsmokers, and parents’ weight also influenced blood pressure. Breast-feeding was associated with a lower blood pressure.

Collectively, the findings suggest a need to start heart disease prevention efforts early in life, rather than after risk factors have become well established.

“The impact of these data may be far reaching,” said lead author Sarah de Ferranti, M.D., M.P.H., in the cardiology division at Children’s Hospital Boston. “[Medical] practitioners should be aware of the clustering of metabolic abnormalities in children, and affected children should receive risk-reducing interventions.”

The metabolic syndrome is defined by the presence of multiple heart disease risk factors: impaired fasting glucose, high blood pressure, low HDL, elevated trigylcerides, and obesity (measured by waist circumference). A person who has at least three of the risk factors meets the criteria for the diagnosis of metabolic syndrome.

The metabolic syndrome has been studied extensively in adults, but far less in children and adolescents. Researchers adapted the criteria for adult metabolic syndrome to children, then applied them to participants aged 12 to 19 years in the third National Health and Nutrition Examination Survey (NHANES III), conducted between 1988 and 1994.

Overall, 63.4 percent of the children and teenagers had at least one metabolic abnormality, said senior author Nader Rifai, Ph.D. Nearly one-third (31.2 percent) of overweight/obese adolescents had the metabolic syndrome.

The most common risk factor was a low level of HDL (good) cholesterol, seen in more than 40 percent of boys and girls. About 30 percent of adolescents had elevated levels of triglycerides, another type of blood fat, and between 20 percent and 30 percent of adolescents had a waist circumference that met the definition of obesity. Additionally, 9.2 percent met the criteria for metabolic syndrome (three or more risk factors), which occurred almost equally in boys (9.5 percent) and girls (8.9 percent), and in older (8.3 percent) and younger (10.3 percent) adolescents.

The distribution of metabolic syndrome by ethnic group was Mexican-Americans – 12.9 percent, non-Hispanic whites – 10.9 percent, and non-Hispanic blacks – 2.5 percent. These percentages for adolescents are similar to those reported in adults from the same ethnic groups.

Because metabolic syndrome is closely related to diabetes and obesity, the “results are not surprising in view of the high and rising rates of obesity and type 2 diabetes mellitus in U.S. children,” de Ferranti said.

In the second study, Debbie A. Lawlor, M.B., Ch.B., Ph.D., consultant senior lecturer in epidemiology, department of social medicine, University of Bristol, United Kingdom, and colleagues, reviewed parental and early-life factors that influenced blood pressure in children at age five. Interest in blood pressure at such an early age comes from the recognition that high blood pressure is a major risk factor for heart disease, and blood pressure in adults tends to follow the same pattern seen in childhood. Previous studies of blood pressure in childhood have tended to involve relatively few children, used different types of study designs and produced inconsistent results.

The study involved more than 8,500 Australian women and their offspring enrolled in the Mater-University (Queensland, Australia) study of pregnancy and outcomes. The investigators evaluated a variety of variables for their potential influence on childhood blood pressure. The factors included ethnicity, smoking history, mother’s height and weight, father’s body mass index, family education, income and a variety of other factors. At age five, 3,864 offspring were examined.

Children of women who had smoked throughout pregnancy had a systolic blood pressure (the first number in a blood pressure measurement) that was about 1 millimeter of mercury (mm Hg) –or point – higher at age five, compared to children whose mothers did not smoke during pregnancy. A comparison of women who quit smoking during pregnancy with those who continued suggested that quitting during pregnancy could prevent the adverse effect on offspring blood pressure.

A mother’s age was associated also with higher blood pressure. A child’s systolic blood pressure was 0.7 mm Hg higher for every additional five years of age in women at the time they gave birth, Lawlor said.

Breast-feeding for at least six months was associated with lower blood pressure. Other factors associated with blood pressure were the mother’s weight and height, the father’s weight, and the child’s weight, height, and body mass at age five.

The findings have implications for childhood prevention strategies that might yield benefits into adulthood, the investigators concluded.

“Since childhood blood pressure tracks into adulthood, interventions aimed at early life risk factors – quitting smoking during pregnancy, breast-feeding, prevention of obesity in all family members – may be important for reducing the population distribution of blood pressure, and thus cardiovascular disease risk,” said Lawlor.

De Ferranti’s and Rifai’s co-authors are Kimberlee Gauvreau, Sc.D.; David S. Ludwig, M.D.; Ellis J. Neufeld, M.D., Ph.D.; and Jane W. Newburger, M.D., Ph.D. This study was partly funded by the National Institute of Diabetes and Digestive and Kidney Diseases.

Lawlor’s co-authors are Jake M. Najman, M.D.; Jonathan Sterne, Ph.D., B.Sc.; Gail M. Williams, Shah Ebrahim, M.D.; and George Davey Smith, M.D.