Mother's milk contains omega-3, but the amount can vary depending on how much omega-3 the mother eats. DHA is very important for the development of the brain in fetus and infant. Infant formula does not contain any omega-3. This is why the World Health Organization recommends in its report from 1995 that 40 mg of DHA per kilogram of infant body weight, should be added to the milk to make it more like mother's milk.
Oily fish is rich in DHA, and vegetarian women who don't eat fish have less DHA in their milk than non-vegetarians (Reddy et al.). Inuit women who normally eat lots of fish also have a very high amount of DHA in their milk (Innis et al.). A Danish study of 8 729 pregnant women investigated whether there was any connection between intake of fish and preterm delivery and low birth weight. In this study it was concluded that a low consumption of seafood was a strong risk factor for both preterm delivery and low birth weight (Olsen, Secher).
Children that were breastfed for eight months, or more, had a higher intelligence at eight and nine years of age, better reading comprehension, mathematical ability, and scholastic ability at 10 to 13 years of age. They also scored better results at school leaving examinations compared to children who were bottle-fed. These results come from an 18 years long study from New Zealand (Horwood, Fergusson). The researchers believe that it is because of the polyunsaturated fatty acids in the mother's milk, and especially the DHA, that the breastfed children scored better results.
Dr. Barbara Levine thinks that it's important for pregnant and lactating women to eat extra DHA, since it is important for the development of the brain and eyes in fetus. The human body needs DHA during the whole lifetime, but it is especially important at the end of the pregnancy, when the brain is developing. Furthermore, Levine says that a deficiency of DHA can lead to ADHD, and possibly even low intelligence for the child. For the mother it can lead to an increased risk of postpartum depression.
American women have very small amounts of DHA in their milk. This is probably because of the typical American diet, which is often very low in DHA. When a woman is pregnant and breastfeeding she transfers her DHA to the child. Therefore, Levine says that women should eat extra much DHA during this period. She also says that experts recommend an intake of fish two to three times per week, and if you don't eat enough fish you could take 100 mg DHA per day as a supplement.