Written by: Anna Petherick, Ph.D. | Issue # 53 | 2016
- A new study finds differences in the hearts of adults who were born premature and fed formula, from the hearts of adults also born premature but fed breast milk from birth.
- In general, both of these groups had less well functioning hearts compared with hearts of people who were born at full term. However, those fed breast milk as preemies had far more “normal” hearts.
- The study adds to other evidence making the case for premature infants to receive breast milk in their first weeks of life, either expressed by their own mother, or donor milk.
Thanks to improving knowledge and standards of care in hospitals, babies born several weeks before their due dates are more likely than ever to survive. This trend has come with the loose assumption that, once through early life, individuals born premature grow like children born at term, living just as long and as healthily.
But in the past few years, evidence has come to light showing that preterm infants grow in subtly different ways from infants born at term. In 2013, for example, Adam Lewandowski of Oxford University and his team of medical scientists demonstrated that, as young adults, those who were born early tend to have hearts that are a bit heavier than hearts of individuals born at term, though with smaller chamber volumes and weaker functioning.
In their most recent study, published in June 2016 [1], the same team considered why preterm babies’ hearts might develop differently. They thought that the nutrition provided in the neonatal intensive care unit (NICU) might be a factor. Specifically, the team wanted to know if preterm infants who were fed only breast milk during their stay in the NICU have more “normal” hearts as adults compared with those who were fed infant formula during the same period of their lives.
To figure this out, the researchers set about re-analyzing data from their 2013 studies [2,3] taking into account early feeding regimes. In these studies, the team contacted people born between 1982 and 1985 who had originally participated in a clinical trial that investigated the effects of early diet on cognitive development. As such, these individuals had weighed less than 1,850 g at birth, and spent the first weeks of their lives in one of five NICUs in the UK. While they were in the NICU, some had been randomly assigned to exclusively receive breast milk, and others to receive infant formula.
The results of the new data analysis come with a dose of caution. Only 102 of the 926 people who were enrolled in the original trial as preterm infants could be contacted and convinced to spend a day in Oxford having their heart scanned by an MRI (magnetic resonance imaging) machine. For this reason, Lewandowski and his team urge tentative interpretation of their findings. Nonetheless, the size of the effects and reasoning that has been put forward to explain them are noteworthy.
Compared with healthy adults of the same ages, sizes, and sexes who were born full term, the individuals born early had slightly different heart structures—as described in the 2013 studies. They also had higher blood pressure, and altered blood biochemistry profiles. But the differences were relatively slight for individuals who were premature and, while in the NICU, had exclusively consumed breast milk. For example, both milk-fed and formula-fed preemie groups had smaller left ventricle volume as adults than those born at term. But the reduced size for the milk-fed group was 9%, whereas that of the formula fed group was 18%.
There were various other differences between the breast milk- and formula-fed groups. The formula-fed individuals had bigger pulmonary artery diameters, and their ejection fractions from their right ventricle—a measure of how well the heart pumps blood out of it and around the lungs—were smaller. Meanwhile the ejection fractions of the right ventricle of the breast milk-fed group were no different from those of individuals born at term. Moreover, the overall chest cavity dimensions of the formula-fed group were smaller than those of the breast-milk fed group—and again, the breast-milk-fed group was no different by this measure from those of the full-term-born group.
The finding about chest cavity differences is important because it hints at a mechanistic explanation for the overall differences. The heart’s physiology is intimately connected with that of the lungs. Out of the right ventricle, blood is carried around the lungs to pick up oxygen. It then travels back to the heart, where the powerful muscular walls of the left ventricle pump it around the body.
Lewandowski and his coauthors write that those who were fed formula as premature infants did not receive the growth factors—such as vascular endothelial growth factor—that are present in breast milk. And for this reason, they probably had slightly abnormal vasculogenesis (the development process that gives rise to the heart and blood network) and angiogenesis (remodeling and expansion of that network) during early development. These two processes have also been linked to poor lung development in preterm infants. Hence, the finding of greater differences with preemie feeding regime between the right side of the heart and the left: the right ventricle’s power must be commensurate with lung size and function, so as to push blood around the lungs at the appropriate pressure. If the formula-fed individuals have less well-developed lungs, their right ventricle growth would be restricted.
Although the study didn’t test this, the differences identified are probably noticeable in the participants’ physiological performance, during peak exercise, and as they cope with the effects of age and modern living on their cardiovascular systems. It is only logical that the lower end-diastolic volumes and stroke volumes—essentially, the lesser pumping abilities—of the hearts of adults who were fed formula in the NICU will lower their maximal exercise capacity throughout adult life. And maximal exercise capacity is itself an independent predictor of mortality and cardiovascular health into old age.
So, while the number of adults evaluated in this study was indeed small, and infant formulas have improved substantially since the early 1980s, the policy implications of this research are clear and simple. Babies in the NICU should be fed breast milk whenever possible, including donor milk if their own mothers have problems expressing, or do not wish to express.
Commenting on the paper in the British Medical Journal, Russell Viner, a professor at University College London’s Institute of Child Health, said that this research adds to other studies that have concluded the same policy recommendation. “For premature babies who are born before they are physically ready for life outside the womb, breast milk is incredibly important. It protects an already vulnerable baby from infections and leads to a range of later beneficial effects on the brain, blood pressure and bone strength,” he said [4].
References
1. Lewandowski A.J., Lamata P., Francis J.M., Piechnik S.K., Ferreira V.M., Boardman H., Neubauer S., Singhal A., Leeson P., Lucas A. (2016) Breast milk consumption in preterm neonates and cardiac shape in adulthood. Pediatrics 138(1): e20160050.
2. Lewandowski A.J., Augustine D., Lamata P., Davis E.F., Lazdam M., Francis J., Leeson P. (2013) Preterm heart in adult life: cardiovascular magnetic resonance reveals distinct differences in left ventricular mass, geometry, and function. Circulation 127(2): 197–206.
3. Lewandowski A.J., Bradlow W.M., Augustine D., Davis E.F., Francis J., Singhal A., Lucas A., Neubauer S., McCormick K., Leeson P. (2013) Right ventricular systolic dysfunction in young adults born preterm. Circulation 128(7): 713–720.
4. Wise, J. (2016) Breastfeeding premature babies improves their heart function as adults, study shows. British Medical Journal 353: i3307 doi: 10.1136/bmj.i3307.