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Fatty acids enhance retinal function and vision in infants
Increased intake of DHA in preterm infants provides the strongest evidence.
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PORTLAND, Ore. — Both animal and human studies have documented beneficial effects on retinal function and vision when infants are fed formulas containing ample omega-3 fatty acids.
“Intake of these particular fatty acids during infancy appears to be important for optimal retinal development, and perhaps also brain development,” said Martha Neuringer, PhD, a research associate professor of medicine and ophthalmology at Oregon Health Sciences University in Portland. In addition, “a particular long chain omega-3 fatty acid, called docosahexaenoic acid [DHA] is found in extremely high levels in the retina, especially in photoreceptors.” In fact, DHA can represent between 50% to 60% of the total fatty acids in the major phospholipids of photoreceptor disk membranes.
Dr. Neuringer is the author of a recently published article in the American Journal of Clinical Nutrition that reviewed a number of monkey and human studies that evaluated the relationship between infant vision/retinal function and long-chain polyunsaturated fatty acids (LCPUFAs). The review described the methodology, neural basis, and interpretation of two primary visual measures used to assess the efficacy of infant formula LCPUFA supplementation: the electroretinogram and visual acuity. “There also are other measures of visual development that may be used to extend the functional evaluation of infants fed formulas with different fatty acid compositions,” Dr. Neuringer told Ocular Surgery News.
Comparison of infant formulas
Through her monkey studies, Dr. Neuringer demonstrated the hypothesis that diet-induced alterations in retinal fatty acid composition lead to changes in retinal function. Moreover, a 1992 published study by Birch and associates assessed retinal development in very low birthweight infants that were fed diets differing in omega-3 fatty acids. The authors found that preterm infants fed a corn-oil-based formula low in omega-3 fatty acids had lower maximum amplitudes, lower sensitivity and an increase in the threshold of the rod electroretinogram compared with infants receiving either breast milk or a marine-oil-supplemented formula containing omega-3 LCPUFAs. “The babies that were fed the corn-oil-based formula had a retinal function that appeared to be less mature,” Dr. Neuringer said.
This study also found that acuity development also appeared to proceed more quickly in preterm infants fed high amounts of alpha linolenic acid (ALA), and even more rapidly in those supplemented with omega-3 LCPUFAs. “ALA is the precursor of DHA,” Dr. Neuringer said. “ALA is the omega-3 fatty acid that is in vegetable oils and currently present in infant formulas in North America. When we first realized that omega-3 fatty acids had this specific role in the retina and visual development, we were concerned whether infant diets were providing enough precursor, the ALA.” As a result of early monkey studies, “the amount of ALA in infant formulas was increased,” she said. At the time, “it was high in some formulas and very low in others. The minimum has since been increased so that now all formulas provide a reasonable amount of the ALA.”
ALA vs. DHA
The focus then shifted to determining whether DHA, rather than ALA alone, should be added to infant formulas. Birch and associates found that at 4 months past term, preterm infants fed a soybean-oil-based formula that was relatively high in ALA had poorer visual evoked potential acuity than the LCPUFA-supplemented group. “This is evidence to suggest that it is better to provide DHA that is already pre-made in the diet instead of only providing its biochemical precursor, ALA,” Dr. Neuringer said.
A 1993 published study by Carlson and associates used the acuity card procedure to evaluate visual acuity longitudinally at 2, 4, 6, 9 and 12 months post-term in preterm infants fed a soybean-oil-based formula compared with those supplemented with a marine oil. Supplemented infants had significantly better acuity at 2 and 4 months, but not at later ages. “Early acuity development was accelerated by dietary LCPUFAs,” Dr. Neuringer said. In addition, “the studies in preterm infants are quite consistent in showing that DHA is better. However, there is a very important caveat. It now appears that DHA needs to be combined with arachidonic acid, which is an omega-6 fatty acid. Those two fatty acids also need to be provided in the right balance. If you have too much of one, you actually can suppress the other.”
Nonetheless, “it is not clear whether differences in acuity or other visual abilities persist over the long term,” Dr. Neuringer said. Previous research on visual development “suggests that changes early on can affect visual development or brain development in life,” she said. In addition, randomized studies examining the effects of LCPUFA supplementation among term infants have found conflicting results. “Some studies have found benefits, others have not, so it is an unresolved issue,” Dr. Neuringer said.
Breast milk provides both DHA and arachidonic acid. However, there also are many differences between breast milk and formula that cannot be attributed solely to omega-3 fatty acids or LCPUFAs. “Formulas differ nutritionally and biochemically from breast milk in numerous ways,” Dr. Neuringer said. Moreover, “these dietary differences are invariably confounded by socioeconomic and psychologic factors.”
Even though LCPUFAs are part of breast milk, “none of the formulas in North America contain them at this time.” One of the problems has been finding sources that can duplicate the composition in human milk. “There also was concern about potential side effects of the sources,” Dr. Neuringer said. Regardless, “I think now there is sufficient beneficial evidence to include LCPUFAs for preterm infants. I would expect a report from the Food and Drug Administration within the next year. But human milk is still the optimal food for infants.”
For Your Information:Reference:
- Martha Neuringer, PhD, can be reached at Oregon Health Sciences University, 505 N.W. 185th Ave., Beaverton, OR 97006; (503) 690-5360; fax: (503) 690-5563; e-mail: neuringe@ohsu.edu. Dr. Neuringer has no direct financial interest in any of the products mentioned in this article, nor is she a paid consultant for any companies mentioned.
- Neuringer M. Infant vision and retinal function in studies of dietary long-chain polyunsaturated fatty acids: methods, results and implications. Am J Clin Nutr. 2000;71(suppl):256S-267S.