Researchers uncover a key reason why women develop depression during pregnancy

While for many women pregnancy is a time of joy, for others, it brings on depressive symptoms, such as feelings of sadness and lethargy, sleep disturbances and changes in appetite. In fact, according to The American Congress of Obstetricians and Gynecologists, 14 to 23 percent of women struggle with depression during pregnancy. A myriad of factors contributes to mental health, of course, but researchers at the University of Ohio have zeroed in on one key factor: low levels of a protein in the brain called BDNF, or brain-derived neurotropic factor.

This protein has already been shown to affect mood and play a role in depression. In pregnancy this protein has another special job: it’s involved in the development of the placenta and the growth and development of the baby’s brain. Lisa Christian, a psychologist and researcher at Ohio State University, and her team decided to take a closer look. They studied the levels of BDNF in 139 pregnant women and found that levels of the protein went down in all women during pregnancy. This makes sense, says Christian, because the baby is using the protein for the placenta and brain growth.

She and the other researchers noticed, however, that the women whose BDNF levels decreased the most had more significant depressive symptoms in late pregnancy. The fact that the levels of BDNF started to fall in the second trimester, before the depressive symptoms started, suggests this protein actually plays a role in causing the symptoms. “Then the low BDNF is also seen even more considerably in the third trimester concurrently with the depressive symptoms,” adds Christian.

The levels of BDNF increase again postpartum, and the researchers didn’t see any statistically significant associations between BDNF and postpartum depression (they followed the women until 6 to 8 weeks postpartum.) But Christian says the levels of BDNF and the effect on women’s moods postpartum warrants more attention. “We will be looking at this,” she says.

In the study, she also found that lower levels of BDNF levels were associated with low birth-weight babies. This could be because BDNF is important for the development of the placenta, and if the placenta is affected by low BDNF levels, that could affect the baby’s growth.

So if you are pregnant, is there anything you can do to safeguard this special protein? It appears that the protein is influenced by diet and lifestyle.

“Exercise has been shown to really considerably increase BDNF levels in studies,” says Christian. As for diet, animal studies show that a diet higher in omega-3 fatty acids and lower in sugar contributes to healthy BDNF levels. (Antidepressants can also increase BDNF levels, but some have been linked to health problems in babies and they are only prescribed after weighing the benefits versus the risks.)

While doctors won’t be testing a woman’s BDNF levels during pregnancy (the marker is helpful for looking at things across populations, but it doesn’t add a lot of value to know an individual’s BDNF because the level varies with other factors, such as race) this link is an important discovery. “It's helping us understand what some of the causal mechanisms [of] might be,” says Christian. “Women can see that we have a real effect on a specific biomarker that we know supports the mom and that we know supports the baby. This might provide them with some more concrete motivation to take care of themselves.”

Read more: Could there be a simple way to prevent depression during pregnancy? Antidepressants during pregnancy raises autism risk Parenting through severe postpartum depression