During pregnancy a mother's reserves of DHA are used to assist with brain development in the foetus, particularly in the third trimester, leaving them depleted. By the time the baby is born, blood DHA levels in the mother can be very low, which then impacts on the DHA content of breast milk.
Over the last few decades scientists have noticed a steady decline in the Omega-3 content of breast milk combined with a rise in Omega-6, changes that are likely to have an impact on DHA intake in babies. This change has been blamed on low intakes of seafood and high intakes of vegetable oils and margarine.
There is some evidence that a low-DHA status after pregnancy could increase the risk of post-natal depression, as new mums who developed the condition were found to have low levels of DHA in their blood. Other kinds of depression may also have a link with a poor DHA status, with studies finding that people diagnosed with clinical depression have low levels of DHA in their blood.
In order to top up levels of DHA, pregnant women should be encouraged to eat more seafood, especially oil-rich fish, whilst being aware of the species to avoid during pregnancy. It's believed that if the UK doubled its intake of seafood, the incidence of post natal depression could be reduced from an average of one in six live births to one in twelve.