Infants and preschoolers who gain weight rapidly may have higher-than-average high blood pressure later in childhood, a U.S. study suggests.

The relatively small differences in blood pressure linked to rapid weight gain for youngsters in the study may be tied to an increased risk of other health problems in young adulthood, such as high cholesterol or elevated blood sugars, say the authors of the study.

The researchers tracked changes in weight and height for 957 babies up to age four and found the children who gained excessive weight for their height, as reflected by higher body mass index (BMI), tended to have higher blood pressure than peers at ages 6 to 10 years.

Each additional increment of BMI gained as an infant or toddler was linked to an increase of about 1 to 1.5 mmHg (millimeters of mercury) in systolic blood pressure.

"Previous studies have emphasized the importance of rapid weight gain in early infancy in determining later blood pressure; the current study adds to emerging data that weight gain during the preschool years is at least as important as infancy weight gain in relation to blood pressure," said senior study author Dr. Mandy Belfort of Brigham and Women's Hospital in Boston.

Linear growth - when children add pounds at a steady pace - doesn't appear to be a problem for childhood blood pressure, Belfort added by email. Instead, the culprit may be sudden surges in weight that aren't matched by increases in height.

"Our finding that gain in body mass index, not linear growth, predicted later blood pressure suggests that more rapid accumulation of fat may be important," Belfort said. "Our research does suggest that more is not always better when it comes to weight gain in babies."

Belfort and colleagues reviewed data from medical records starting when babies were born. On average, the kids were around 8 years old at the mid-childhood checkup, with average systolic blood pressure (the top number) of 94.4 mmHg and average diastolic blood pressure (the bottom number) of 54.3 mmHg.

While ideal blood pressure for children at any given age varies by gender and height, this average for 8-year-olds would be in a range generally considered healthy.

High blood pressure is harder to detect in children than in adults. In adults, 140/90 or greater is considered high. There's no single cut-off in children, however. In general, children with blood pressure higher than 95 percent of children of the same gender, age and height can be diagnosed with high blood pressure. Since children's blood pressures will vary greatly based on these factors as they're growing up, there is no set range that defines normal or high.

Kids in the study who experienced unusually large surges in BMI before 6 months of age or between ages 2 and 3 years had higher systolic blood pressure in mid-childhood then their peers who experienced steadier growth throughout those periods.

The magnitude of the increase in systolic blood pressure was larger for the preschoolers than the infants, the study also found.

Birth size didn't appear to influence the results.

One limitation of the study is that it can't prove that rapid increases in BMI directly caused higher blood pressure, only that there was a connection between the two things, researchers acknowledge in the journal Hypertension.

Still, the findings support recommendations that mothers breastfeed infants until age 6 months because this is linked to less weight gain than formula feeding, noted Caryl Nowson, a diet and nutrition expert at Deakin University in Australia who wasn't involved in the study.

Once young children move on to solid food, parents should avoid giving kids soft drinks and limit consumption of fruit juice, both of which can contribute to weight gain, Nowson added by email.

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