DHA & ARA
There are many factors that play important roles in infant nutrition and neurological development. Vitamins and minerals, such as iron and iodine, for example, are essential. But one of the most exciting discoveries in the past generation of research involves the role of fatty acids, such as DHA, which are the building blocks of fats and oils found in nature. The fatty acids that have gotten the most public attention are the ones touted in fish oil. These compounds are actually produced by algae, which is a vital part of the aquatic food chain and the reason that these fatty acids are eventually concentrated in oily fish.
There are many different fatty acids found in nature, however. Two fatty acids in particular are called “essential fatty acids,” because the human body can’t make them and must therefore get them through the diet. These are linoleic and alpha-linolenic acid and they are found in many types of plant-seed oils. From these two fatty acids, which chemists describe as polyunsaturated fatty acids (PUFAs), the body can assemble long-chain polyunsaturated acids (called LCPUFAs) such as DHA (docosahexaenoic acid) and ARA (arachidonic acid). Researchers believe that an infant’s body, however, does not convert PUFAs into DHA very effectively or in sufficient quantity to meet the needs of the infant’s rapidly growing brain.
The story of the role of DHA and ARA in infant nutrition has unfolded over the past three decades. Researchers discovered that DHA and ARA, which are found in cell membranes, become concentrated in the fetal brain during the last trimester of pregnancy, a time when there is an extraordinary increase in the growth of neurons in the brain. Researchers also found that DHA and ARA appear to play a role in the development of vision (studies in rats and monkeys showed that diets that excluded key fatty acids resulted in retinas that didn’t develop or function properly).
“The importance of DHA as a part of proper infant nutrition came to the fore in the 1980s,” explains Tom Brenna, professor of human nutrition at Cornell University, “when medical technology developed to the point where very premature infants, less than 2 lbs, began to survive at very significant rates. A baby that small is born at 6 months and has its last trimester after it is born. That last trimester is the developmental period when the brain starts depositing DHA exponentially. Those babies were in an incubator being fed a formula that did not include any LCPUFAs, which meant that the preterm infants had to make all of their DHA from precursor fatty acids.”
The newfound ability to keep very low weight preterm babies alive became an opportunity to see the importance of fatty acids such as DHA and ARA to the developing infant. Researchers found that increasing the amount of DHA in the diet of the infant or in the diet of the mother while pregnant delivered more DHA to the baby. And this in turn could be measured in changes in the development of the visual system as well as cognition.
Studies have shown that DHA in cell membranes not only encourage nerve growth (neurogenesis) but also plays a key role in the development of the synapses, or connections, between nerves (synaptogenesis). Each neuron can have hundreds or even thousands of connections with other neurons. Synapses are the connections through which neurons signal other neurons in the brain as well as other cells such as muscles. In this way, synapses create the network of circuits within the brain, which gives rise to thought and perception, and throughout the central nervous system, which allows the nervous system to communicate with the rest of the body. And although synaptogenesis occurs throughout a healthy person's lifespan, there is an explosion of synapse formation during early brain development.
DHA and ARA are fascinating fatty acids because they represent such a tiny fraction of the total fat in human milk and infant formula and yet their purpose in infant nutrition and development is so specific. DHA and ARA make up a third of the fatty acids found in brain grey matter and up to two-thirds of those found in the eye’s retina. But researchers have also discovered that DHA levels in breast milk vary greatly in different regions. For example, DHA levels in Australia have been measured at 0.23%, in the U.S. at 0.17% and in Japan at 1.0%. Among the lowest DHA levels recorded was 0.07% in Sudan, and even within a large country such as China, levels ranged from 0.44% to 2.78%. The reason for the variation is believed to be due to differences in diet, especially fish consumption, with DHA levels in some areas declining significantly because of changes in traditional diets. One comprehensive review found a worldwide average of 0.32%.
A natural question, says Brenna, is how much DHA is enough for proper infant nutrition? “We produce a basal amount of DHA. That’s clear. And we know this because we don’t see deficiencies in people who don’t eat any animal products at all. Those people have babies that are healthy. So it seems like our biochemistry is tuned to provide a more or less minimal amount of DHA to prevent obvious signs of deficiency. But our biochemistry also seems to rely on a supply of DHA to optimize our development.”
So the related question, says Brenna, is, how much DHA is optimal for complete infant nutrition? “One of the observations that people have made about certain development periods is that when we compare consumption of DHA with consumption of only
precursors, we find that babies that consume DHA develop a little faster, but babies not eating DHA end up at the same point eventually.” If that is the case, and it seems to be with certain elements of development like visual acuity, is there any reason to be worried about DHA?
Vision also provides a good example of one mechanism by which DHA acts. “In the retina, DHA is in highest concentration in what we call the photoreceptors,” explains Brenna. “Photoreceptors are cells stimulated by light. The molecule in the photoreceptor that detects light, the energy of the photon, is a protein called rhodopsin. This molecule of rhodopsin is embedded in membrane and surrounded by phospholipids that contain DHA. The DHA interacts with the rhodopsin molecule in a way that facilitates the transfer of the signal from rhodopsin to the other membranes of the cell, which then amplify that signal and this ultimately results in the transmission of the nerve signal indicating that a photon has been detected in that photoreceptor.”
There is still a great deal to learn about exactly why and exactly how fatty acids in breast milk, like DHA and ARA, are important in infant nutrition and development. Although DHA seems to be getting all the attention, says Brenna, we know that ARA also has many functions. “It is best known for its properties as a signaling molecule or as a precursor for lots of other signaling molecules. These signaling molecules are best known for blood clotting and they are also involved in inflammation. ARA is also found at very high levels in the brain.” Not all of ARA’s functions are completely understood, notes Brenna, but we do know that ARA is also part of the ongoing story of researchers trying to tease out the role and function of key nutrients in infant nutrition and fetal and infant development. It is a story with many chapters yet to be written.
Infant Nutrition (VIDEO)
Fueling Growth & Development
Milk Enters the Stomach
Milk Enters the Small Intestine
Some Key Nutrients
Gut & Immune Development
Skeletal & Muscular Development
Skin & Hair Growth
The Importance of Fat
DHA & ARA
Nervous System Development
Good Nutrition Builds Healthy Babies
Related Health Centers:
Infant Nutrition Health Center, Mother-Baby Bond Health Center, Mother’s Milk Health Center, Monthly Infant Development Calendar Health Center,Weekly Pregnancy Calendar Health Center