Breast-feeding a baby helps new mothers fight depression, according to research at the University of New Hampshire.

Author Kathleen Kendall-Tackett said omega-3 fatty acids can also help women fight depression.

She said that one of the causes of depression is an increase in inflammation because of hormones called proinflammatory cytokines. Levels of cytokines increase at the end of pregnancy and after giving birth.

"Breastfeeding protects maternal mood by lowering stress. When stress levels are lower, the mother's inflammatory response system will not be activated, thereby lowering her risk of depression," Kendall-Tackett said.

The author said that post-partum depression is common in many cultures, affecting 10 to 20 percent of women.

She said, however, that the benefits only came when breast-feeding was successful. Trouble getting a baby to eat or pain could increase stress and make depression more likely.

The full report is available from the International Breastfeeding Journal.