Parents and doctors alike fret over especially low-birthweight newborns. Their diminutive size means these babies have little energy reserve—body fat—to sustain them during illness or throughout fussy eating patterns. A trend has therefore developed to fortify the formulas fed to such tiny babes. The booster beverage contains extra nutrients and protein. Unfortunately, a British study finds, this practice could have a negative long-term repercussion: high-blood-pressure in adulthood.
Between 1993 and 1995, Atul Singhal of the Institute of Child Health in London and his colleagues recruited 299 full-term newborns each of whom weighed in the bottom 10 percent of babies born at the same gestational age. Such babies tend to have had a low rate of growth throughout their development in the womb. The babies' moms had decided not to breastfeed.
Half of these children were assigned to get normal infant formula for 9 months; the rest received formula fortified with nutrients and 28 percent more protein than the standard formula. The growth of all of these children was compared to that of 175 similarly low-birthweight babies whose mothers had chosen to breastfeed their children for their first 9 months. Six to eight years later, the researchers located the children to give them a series of measurements and biomedical tests. They found 83 babies from the normal-formula group, 70 babies from the fortified-formula group, and 95 babies from the breastfed group.
"Originally, when this project was set up, we had expected that by getting these small babies to grow as fast as we could, we'd see benefits," notes Singhal. To his surprise, he told Science News Online, within a few years of beginning the study, data began accumulating from other trials by his group and others that indicated "exactly the opposite was true." In the latest data, children who had received fortified formula had significantly higher blood pressures than those in the other two groups. Singhal's team reports its findings in the Jan. 16 Circulation.
Similar blood-pressure elevations have been associated with accelerated weight gain in at least six other studies that examined preemies or babies that had not been randomly assigned to a particular feeding regimen.
Singhal's latest work is the first of these studies to follow healthy, full-term infants and to randomly assign them to one feeding regime or another. Randomization is important, Singhal points out, "Because it lessens the chance that some type of bias was introduced" by assigning participants with certain characteristics to one group or another.
Changes were dramatic
Singhal and his colleagues measured not only conventional systolic and diastolic blood pressure—the peak number and lower, background number, respectively—but also the mean arterial pressure. In the new study, all three measures were highest in the fortified-formula group, somewhat lower in the breast-fed group, and lowest of all in children who had received standard infant formula.
The biggest differences showed up in the diastolic and mean arterial pressure: They averaged 3.5 and 3 millimeters of mercury (mmHg) higher, respectively, for children fed fortified formula compared to those who had received standard formula during their first 9 months of life.
It's important to note, Singhal says, that none of the children had what doctors would consider high or unhealthy blood pressure. However, he notes, blood pressure tends to climb with age and "to track from about 6 to 8 years of age. So, if you're at the top of a particular cohort at 6 to 8, you'll also be at the top of that group as an adult."
Blood pressure correlates with risk of cardiovascular disease. Among adults, lowering population-wide diastolic blood pressure by only 2 mmHg would be expected to prevent some 100,000 heart attacks and strokes per year in the United States, Singhal's group calculates. "The present study therefore has important implications for infant nutrition policy," they conclude.
Singhal finds further reason for concern in an animal study published in Nature 3 years ago. In this trial, conducted at the University of Cambridge in England, some mice were born small because their moms' diets had been restricted during pregnancy. A portion of these infant mice were subsequently overfed as infants by letting them nurse from unrelated, fully-fed females that had given birth to litters of healthy-weight offspring. This allowed the tiny mice to catch up their weight to that of mice that had been well nourished in the womb—but there was a cost.
"Mice who underwent fetal-growth restriction but which were cross-fostered at birth to normally fed dams experienced rapid catch-up growth [but] died at a younger age than controls," the study's authors reported. Mice in the opposite situation—well fed in the womb but nursed by malnourished females—lived longer than did the other mice, even those that were normally nourished from conception onward.
Moreover, fetal-growth-restricted mice that nursed on the catch-up or normal mother's milk overate as adults when given unlimited access to food. The result: They became obese and died prematurely. However, giving mice all the food they wanted "had no [detrimental] effect on the longevity of mice whose growth was restricted during suckling," the authors found.
The Cambridge scientists argued that something about the early diets of these mice programmed them to be susceptible to obesity and premature death. Singhal now worries that human babies may be similarly programmed to become overweight and develop higher blood pressure by early feeding habits. Several human trials have indeed shown that when infants are overfed before weaning, they have an increased susceptibility to become obese as youngsters.
His team concludes in its new paper that when it comes to infants, data "support the hypothesis that the promotion of faster weight gain has adverse programming effects"—on blood pressure, and perhaps on much more.
No matter how big a child is at birth, he or she will probably attain the same adult height no matter how quickly the baby grows. But attaining one's adult size at a slow-to-moderate pace may have a host of benefits, Singhal says. His advice to parents: Be patient—don't rush a child's growth.
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Medical Research Council Childhood Nutrition Research Centre
Institute of Child Health
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London WC1N 1EH
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