For centuries, fish has been considered “brain food” in cultures around the world. Generations of children were raised on a daily spoonful of cod liver oil, because their parents had a general sense that it was “good for you.”1
Recent medical research has borne out this traditional wisdom. Today, the scientific community has come to recognize that important compounds contained in fish oils have profound benefits for human brain health, development, and behavior.2
The heart-healthy benefits of omega-3 fatty acids in fish oils have been recognized for more than a decade. More recently, these compounds were found to benefit the vascular endothelium, reducing the risk of stroke and other circulatory conditions.
However, the astonishing effects of omega-3 fatty acids—especially docosahexaenoic acid (DHA)—on human brain health and development have only emerged over the past 5-10 years, as scientists have uncovered powerful evidence that DHA supplementation during pregnancy enhances intelligence, cognition, and visual performance in infants and young children.3 DHA appears to have beneficial effects after birth as well, boosting children’s performance on various intelligence tests.4 Moreover, DHA is also rapidly becoming an important tool in managing teen and adult behavioral problems.5
This article surveys exciting findings from the recent scientific literature that strongly support the brain-health benefits of DHA supplementation throughout the human life span.
Critical Role in Brain Development
Fatty acids make up the largest component of cell membranes, and the brain has the highest concentration of cells found in the human body. Because brain cells depend largely on their membrane composition for proper electrical conduction, brain function is intimately connected to the composition of brain cell membranes.
DHA and arachidonic acid, two fatty acids that are vital for human brain development,6,7 are especially critical during the last trimester of pregnancy and the first few months of an infant’s life. During this period, the brain undergoes a growth spurt, rapidly increasing in mass and its content of DHA and arachidonic acid. DHA in particular is accumulated in the brain’s gray matter (where brain cell bodies are found) and in the retinas of the eyes. A deficiency of DHA in these tissues is known to produce poor vision and delayed psychomotor development.8,9
The developing fetus depends entirely on its mother’s DHA intake for its own supply of this vital brain nutrient. DHA is transferred across the placenta by special transport mechanisms that remove DHA from the mother’s blood at levels higher than for other fatty acids.9 As with most ingested nutrients during pregnancy, the needs of the fetus get top priority and the mother’s body can be rapidly depleted of essential components if adequate intake is not assured. If the mother’s intake is borderline or low, fetal DHA levels will drop.9
During the third trimester, the fetus is estimated to accumulate 67 mg per day of DHA. Current recommendations for DHA intake in pregnant women call for 300 mg or more per day, according to the International Society for the Study of Fatty Acids and Lipids.7 In two recent studies of pregnant women in Canada, average daily DHA intake was only 82-160 mg, and 90% of the women consumed less than the recommended minimum of 300 mg. The low end of the DHA intake range was 24 mg per day.7,10 While mothers’ DHA intake varies around the world, these figures suggest that many women are consuming quantities of DHA that are borderline or inadequate for ensuring optimal brain development in their growing fetuses.
DHA Supplementation During Pregnancy
Since the mid-1980s, animal studies have demonstrated DHA’s critical role in brain development during both the prenatal and postnatal periods, with deficiency states associated with deficits in brain development, vision, and hearing.11-15
Studies of rhesus monkeys have shown that both prenatal and postnatal DHA deficiencies caused reduced visual acuity and abnormal retinal function.16 The same investigations have now shown that, even with postnatal DHA supplementation, retinal DHA levels remained low at three years of life, and levels of retinal electrical activity were below normal. The study authors concluded that prenatal DHA deficiency could have long-term effects on the retina that cannot be reversed by supplementing the infant’s feeding. Prenatal DHA supplements in female rats were shown to protect against experimentally induced brain damage in their infant offspring.17 Such studies emphasize the importance of including DHA in prenatal nutritional supplements.
Numerous human studies have been conducted in response to evidence that fetuses may not get adequate DHA in the critical third trimester. These studies demonstrate that mothers who take DHA supplements have fewer preterm deliveries and give birth to larger, healthier infants who perform better on intelligence and visual acuity tests to the age of at least four years.3
Supplementation with DHA increased the duration of pregnancy by almost one week among a group of women at high risk for preterm delivery.18 Also observed was a trend towards higher birth weight, length, and head circumference in infants born to the DHA-supplemented mothers. Specific evidence of DHA’s impact on newborn brain function comes from a 2002 study, which demonstrated greater maturity of the central nervous system (as measured by sleep patterns) in infants born to mothers with higher plasma DHA levels.19
Mothers who supplemented with cod liver oil containing high DHA concentrations gave birth to infants with significantly higher levels of DHA in their cell membranes,20 and newborns who had the highest DHA concentrations were longer at birth. Newborns who had more “mature” brain-wave testing patterns at birth also had higher DHA levels.
Even more dramatic effects of DHA supplementation during pregnancy are now emerging, with evidence that DHA directly influences cognition and intelligence. In a randomized, controlled, double-blind study,6 women at 18 weeks of pregnancy were given cod liver oil (containing 1183 mg of DHA) or corn oil (placebo) until three months after delivery. All infants in the study were breast-fed until at least three months of age. Children whose mothers received the cod liver oil supplement scored significantly higher on intelligence tests at four years of age than those whose mothers received corn oil. A more complex statistical analysis showed that maternal DHA intake during pregnancy was the only significant variable associated with the mental processing score at four years of age.
In its summary of DHA’s benefits for infant brain development and cognition, an expert panel convened by the Harvard Center for Risk Analysis reached the powerful conclusion that for each increase in maternal DHA intake of 100 mg per day, child IQ (intelligence quotient, a measure of cognitive abilities) increases by 0.13 points.21 This would translate into a nearly 6-point increase in IQ among children of women who supplement with the 4.5 grams of DHA daily that has been used in some trials.22
Like the brain, the eye’s retina consists almost entirely of nerve cells with very high levels of activity, as well as high levels of DHA in its cell membranes.10 While it is impossible to directly measure vision in newborns, the retina’s electrical activity can be measured by means of the visual evoked potential, which matures rapidly in the immediate postnatal period. Infants with higher levels of DHA have more mature patterns of visual evoked potential in the 10-16 weeks following birth.23 Retinal sensitivity to light is also higher in infants with higher DHA levels.24