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A new review of studies finds that supplementing infant formula with omega-3 fatty acids in an effort to strengthen babies' eyesight does appear to benefit early vision development.
However, experts note that breast-fed babies already take in omega-3s naturally from their mothers' milk.
Dr Michael Bloch, an assistant professor at the Yale Child Study Center in New Haven, Conn., and colleagues analysed 19 randomised, controlled trials on nearly 2 000 infants aged 1 year and under. A randomised, controlled study is one in which people are randomly assigned to different groups: one group receives the treatment and the other does not receive the treatment (the "control" group).
"As best we can measure, [the supplementation] seems to help visual development," Bloch concluded.
The study, funded by the US National Institutes of Health, is published online and in the January print issue of Paediatrics.
How the study was done
Marion Nestle, a distinguished professor in the department of nutrition, food studies and public health at New York University, who was not involved with the new study, explained how omega-3 supplementation in formula came to be.
"Formula companies fought hard to get the (US Food and Drug Administration) to allow omega-3s in infant formula so they could use it for marketing - and raise prices," Nestle said. "Now all infant formulas carry it. The omega-3 proponents are eager to prove that it does good. Some studies say yes, some no."
Review author Bloch said he had doubted the need for supplementation with omega-3s, more specifically known as long-chain polyunsaturated fatty acids (LCPUFA).
"I was initially quite skeptical that supplementing infant formula with LCPUFA would produce a measurable difference in infant development in any way, and that maybe [such supplementation] was a waste of money and an unneeded expense for parents," Bloch said.
Findings in the study
However, he added, "based on the findings of the current meta-analysis, I would say that that view was probably wrong and that it's worth spending the money to get a formula supplemented with LCPUFA (which is standard in the United States)."
Assessing infant vision is obviously more complicated than measuring eyesight of older children. Studies in the analysis used behavioural methods or a brain study called visual evoked potential (VEP).
"Behavioural methods rely on observation of infant gaze preferences to determine visual acuity, while VEP examines brain electrical activity," Bloch explained. "Simply put, there is probably more precision and less noise in VEP measures so it has a greater ability to detect a difference."
The brain studies showed a significant benefit on visual acuity from formula supplementation at ages 2 months, 4 months and 12 months, while behavioural tests showed a significant benefit at 2 months.
The researchers had hoped to look at supplementation's effects on vision up to age 18 months but there wasn't enough evidence available. What the findings mean after a baby's first birthday is unclear, NYU's Nestle emphasised.
Long term effects for babies
"The point is that the effect is small but measurable, but its long-term significance is unclear," Nestle said. "Will babies fed omega-3-supplemented formula have better eyesight as adults than adults fed formula before it was supplemented? That's the important question."
Study author Bloch agreed. "Based on the current data available it is difficult to say whether this just gets babies to developmental acuity faster, or to a better endpoint," he said. But these nutrients are important, he added.
"Not all fats are created equal," Bloch said. "Some fats our body can make on its own, and some need to be obtained from our diets." He said that supplementation includes "the two main LCPUFA that constitute an integral structural part of membranes of the cells of central nervous system and retina." These may be particularly important for infant visual development, he noted.
But by no means does this suggest that supplemented infant formula might be better than breast milk, both experts said, or that breast-fed babies would also benefit from omega-3 supplementation.
"Breast milk is high in LCPUFA," Bloch said. "The general goal of formula supplementation is to make it as much like breast milk as possible. . . Clearly, breast-feeding mothers eating a healthy diet is good for their breast-feeding children."
Nestle noted that omega-3s have only been added since the early 2000s. "Until then, formula-fed infants did not get long-chain omega-3s from supplements," she said. "Somehow, they managed to grow up seeing OK. So it's hard to know how clinically significant this is."
Read more:
US hospitals pressured to end free baby formula
Understanding Omega-3 and Omega-6
More information
The American Optometric Association has more about infant vision.
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