Does Sunshine Lower Blood Pressure?

Blood pressure readings were examined from over 342,000 patients at 2,200 clinics over a period of three years beginning in January 2011. Readings were averaged by the month then matched with reports on outdoor temperature and ultraviolet radiation which were averaged into the monthly readings; variables such as gender, age, and BMI were also adjusted for.

Close to 46 million blood pressure readings were analyzed, and findings showed that exposure to UV sunlight was associated with lower systolic blood pressure regardless of the temperature according to lead author Dr. Richard Weller who is a professor of dermatology at the University of Edinburgh. 

According to the researchers this is the first time a large study has shown that vitamin D helps to lower blood pressure regardless of temperature, "half the seasonal variation in blood pressure is independent of temperature. It's due to the UV alone. And that is really exciting." The sunlight effect appeared to be small but significant and with a greater effect among those with lighter coloured skin. 

If a person were to keep their exposure to temperature the same "...you know, nice warm clothing, centrally heated house, etc."—and had summer levels of sunshine in winter, "I reckon that would lower your blood pressure by 2 or 3 millimeters of mercury. Not very much, but a 3-millimeter systolic fall in blood pressure reduces cardiovascular events by about 10%. And you know, that's big."

Weller published another study showing UV light releases nitric oxide in the skin which helps to dilates arteries and lower blood pressure. It is important to keep in mind that unprotected and prolonged exposure during peak times should be avoided. Also this study is an observational study and by nature can’t prove cause and effects. Additionally there may have been room for error in the quality of blood pressure readings taken at the clinics which may not have been done to the same standards as those done in a research setting. 

"Melanomas are bad news," he said. "And that's something all of us dermatologists worry about. But that's not caused by simple sunlight. It's caused by sunburn and intermittent sunlight." Weller said,  "Being outdoors all day long in the sun is normal for us. What is abnormal is the two weeks in Cancun, or the sunbed," and added that dermatologists "need to stop fixating on the harm UV can do and stand back and acknowledge the fact that there is a growing body of evidence showing that it also has benefits on health."