Many moms-to-be—especially those with darker skin or who live in northern latitudes—don’t get enough vitamin D, and deficiency is associated with higher rates of prenatal infections, preeclampsia, preterm birth and Cesarean section. Newborns whose moms were deficient are at risk for low calcium levels and skeletal abnormalities, such as rickets.
“While you should always avoid too much exposure, my advice to pregnant women is to get 10 minutes of sun on their arms and legs daily,” Miller says.
Perhaps surprisingly, the benefits of being in nature include exposure to microbes like Mycobacterium vaccae, a soil bacterium that people may ingest or inhale when in natural environments. These bacteria seem to have antidepressant properties. In one study, researchers injected them into lab animals, which responded by becoming calmer and learning faster.
There’s more: Volatile compounds called phytoncides, which are released into the air by trees such as cedar and pine, seem to enhance human immune function. Researchers in Japan, where nature walks are called shinrin-yoku, or “forest bathing,” found that people who walked in the woods had healthier immune systems, lower blood pressure and lower levels of the stress hormone cortisol compared with people who walked in urban settings.
Lowering stress can be particularly important during pregnancy; one study found that children born to women with high cortisol levels tended to be more anxious. These findings, Miller says, shouldn’t be surprising. We humans, after all, are “part of nature, we’re from nature. When we get out there among the trees and have the wind in our hair and are breathing clean air, we’re much more in balance and at peace.”