A recent study published in the journal Archives of Women’s Mental Health suggests that low vitamin D levels in mothers during pregnancy increases the risk for postnatal depressive symptoms.
Postnatal depression is depression that occurs in mothers after pregnancy, with onset occurring within four weeks of birth and lasting several months to up to a year. Studies have found that 5 to 25% of women suffer from postnatal depression.
Emerging research has shown a correlation between low levels of vitamin D and depressive symptoms. However, most of these studies have only examined the general population, not women specifically and not women after pregnancy specifically.
For example, the researchers in the current study could only find a single past study that looked at vitamin D levels and postpartum mood disorders. This past study was cross-sectional in design and found that low levels of vitamin D were linked to an increase in women reporting postnatal depressive symptoms up to 7 months after giving birth.
In the present study, researchers wanted to build on this lack of research in the area and look into the topic further.
They took blood samples from 929 women after 18 weeks of pregnancy. These women were randomly selected from 2,900 women who were enrolled in the Western Australian Pregnancy Cohort (Raine) Study. The Raine Study is an ongoing study measuring various health markers of women during pregnancy, after pregnancy, and of their offspring.
Every participant in the Raine Study provided information regarding psychosocial and demographic characteristics at the time of enrollment.
A trained midwife recorded detailed obstetric data from the medical records after the participants gave birth, and mothers and their infants were given a clinical examination and brief questionnaire three days post-birth while still in the hospital.
Postpartum depression symptoms were measured by an index of six questions that addressed the following characteristics: anxiety, sadness, mood fluctuations, teariness, appetite changes, and sleep disturbances not related to caring for the baby.
After controlling for certain confounding variables (education level, gender of child, etc.), here’s what the researchers found:
- Lower vitamin D levels at 18 weeks of pregnancy correlated strongly with an increase in depressive symptoms post-birth (p=0.017).
- The women in the lowest quartile of vitamin D status (18.8 ng/ml and lower) at 18 weeks pregnancy were twice as likely (compared to the highest quartile) to report six or more depressive symptoms in the first days following birth.
- The 2nd and 3rd quartiles were not significantly associated with a higher risk for postpartum depression symptoms compared to the highest quartile.
The researchers stated that,
“[The study] provides a novel link in the understanding of the precursors to postnatal depression, as well as greater knowledge regarding the potential role of [vitamin D] in depression more generally.”
They acknowledged their limitations as well. Self-reporting from new mothers who experience mental distress is not always reliable, and lifestyle factors such as sedentary behavior and staying indoors was not measured and therefore not controlled for. Also, because it is an observational study, it can’t establish causation, but it does provide an interesting link between vitamin D levels in pregnancy and the mental health of mothers shortly after birth.
This is the first study of its kind to prospectively measure vitamin D status during pregnancy and compare it to the development of depressive symptoms shortly after birth. That only the lowest quartile of vitamin D levels in the women showed a significant association between an increase in reporting depressive characteristics suggests that there is a threshold for vitamin D levels affecting risk of postpartum depression. Further research on vitamin D supplementation in postpartum depression will help clarify vitamin D’s role.