We already know that being in the sun lowers a person's blood pressure, as well as their risk of heart disease. We now think that this is not to do with Vitamin D, which we also get from sunlight. Instead, it could be a direct effect of sunlight on the skin.
In this study, we have shown that sunlight may do even more: sunlight during pregnancy might help lower the chance of problems with the placenta. This is important, as problems with the placenta can lead to conditions like pre-eclampsia, the baby not growing properly, premature birth and stillbirth.
Sunlight contains a type of radiation called ultraviolet (UV) light. In high doses, this is damaging. However, some UV light is good. We linked information from over 550,000 births with weather data, to work out how much UV light mothers were likely to have been exposed to during pregnancy.
We found that the number of hours in the sun was connected to an increase in weight at birth, and a decrease in preterm birth.
To test this theory further, we also carried out a clinical study with 19 women in the second trimester of pregnancy. Women were exposed to either 30 minutes of UV light, or 30 minutes of “fake” radiation, where the women wore foil blankets to stop the UV light from reaching their skin. In both groups of women, there was a decrease in blood pressure. However, the decrease was greater for the women exposed to the UV light.
Our findings could help shape the advice given to women during pregnancy. Significantly, artificial UV light could be used as a treatment to lower blood pressure in pregnant women, and help prevent pre-eclampsia. We are still looking at the effects of UV light, including how it can influence fertility. In the near future we hope to run a trial studying whether UV light therapy can be used to prevent high blood pressure during pregnancy.
In April, one of the women who took part in this study emailed us to tell us about her experiences:
"Hello dear midwifery research team,
I was part of a study looking at the effect of sunlight on pregnancy and the blood flow through the placenta and have to tell you, it was great. Great doctor and nurse, simply said good experience with I hope beneficial spent time."
This study takes place in a Tommy's centre and is funded by Tommy's and NHS LothianHide details