Postpartum depression (PPD) affects about one in seven women after childbirth in the USA but about one in five in low- and middle-income countries. PPD is a serious mental illness involving the brain that can affect behavior and physical health. People who suffer from depression may experience feelings of sadness, flatness, or emptiness that do not go away and can interfere with their day-to-day lives. Feelings such as these can range from mild to severe.
Research on the relationship between green space and postpartum PPD is limited. Therefore, the purpose of a new study was to investigate the relationship between PPD and green space exposure and the role that physical activity (PA) plays in mediating these relationships.
Study: Association between urban green space and postpartum depression, and the role of physical activity: a retrospective cohort study in Southern California. Image Credit: FotoDuets / Shutterstock
Introduction
It is believed by some scientists that humans need to connect with nature in order to become emotionally stable and de-stress. Undoubtedly, exposure to green spaces is known to benefit mental health, improving outcomes in patients with depression or those under stress.
Most of these findings came from young or older people, typically in the general population. A few studies show that exposure to more green spaces is linked to lower PPD risk. Physical activity is a significant link between green space exposure and mental health. However, other mechanisms might be at work, including stress reduction, feeling part of a group, and reduced pollution.
Earlier research shows that the relationship between green spaces and PPD is a neglected area. Few studies have examined this association, and those were confined to satellite-based assessments of green spaces.
The role of low-lying vegetation has not been considered in most studies, though this is how people typically see greenery around them rather than the downward-facing view from satellites. Moreover, the part played by physical activity has not been measured.
"It is conceivable that eye-level green space can be perceived and experienced to cause physiological responses that could induce relaxation and reduced stress."
Moreover, different types of greenery may affect mental health differently, as shown by one New York study, which showed a better perception of health with greater tree density.
The current study, published in The Lancet Regional Health – Americas, used data from the electronic database of Kaiser Permanente Southern California. They measured green spaces available to pregnant women using various tools, including street views, vegetation types, and satellite-based measures, along with the tree canopy cover and the distance from the nearest park.
What did the study show?
The study included over 400,000 participants with a mean age of 30 years. Half of the population was Hispanic. About one in ten developed PPD, more often in mothers aged >35 years, Black or White (non-Hispanic) mothers, those with middle- or high-income, and those with less than four years of college. Other risk factors include smoking and lower levels of physical activity during pregnancy.
Those who were exposed to more street-level green spaces had a lower PPD risk, as measured by street views. The risk diminished by 2% per interquartile increase in exposure. Other measures, including the Normalized Difference Vegetation Index (NDVI), green land cover, or nearness to a park, did not show this effect.
Green spaces in view of one's house or street are more likely to be seen and experienced during ordinary life and easily accessed during the day. Moreover, besides the scope for physical activity, they are more likely to be associated with social contacts, a safer neighborhood, and lower stress levels.
The effect was stronger with tree coverage, both street-view and total, compared to other types of green space, though the size of the effect was the same at a 2% risk reduction per increase in interquartile exposure.
Trees provide shade, block noise, and reduce air pollution to a major extent. They are larger, provide a greater mass of greenery, and add beauty to a street. They also harbor a diversity of other life forms and are often the hubs of social activity.
Grass and small shrubs or bushes did not appear to have the same protective effect unless within 200m of the home. This could be provided by yards and gardens, provided they are well-kept.
The color and beauty of adequately maintained green spaces could be a de-stressor, improve the mood and prevent mental health deterioration. In turn, this could reduce criminal activity and risky behavior.
So what was the reason for this improvement in risk? The researchers found that physical activity contributed between ~3% to 7% of the effect over all the indicators of green space. The effect was stronger for green spaces in residential areas within 1000m buffer space.
Total NDVI was linked to a potential increase in PPD risk, but this could be inescapable given that it includes all green cover, including large areas of wasteland that are often associated with increased crime rates compared to streets with trees and other green spaces.
Older mothers, White and Asian mothers, and those with higher income and education levels were likely to be exposed to more street-view green space. Trees and bushes were more likely to occur together, but grass cover was not distributed similarly.
What are the implications?
"To our knowledge, this is the first study that examined the relationship between diverse green space measurements, postpartum depression, and the role of physical activity."
The study implies that pregnancy is likely to be followed by PPD less often if the woman has a view of some green space with tree cover. The mechanism of protection may be the increased likelihood of physical activity when there is a green space available for walking nearby during pregnancy.
This study provides a unique insight into the relationship between green space and mental health during pregnancy. "Researchers, city planners, and public health professionals should work together to develop policies and interventions that increase the amount of tree coverage, especially street trees, to create a healthy built environment and optimize the potential benefits of green space for promoting physical activity and maternal mental health." This might be more useful in improving mental health among new mothers compared to planting grass or low bushes.
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