Researchers have found that ultraviolet-A radiation may help to mobilize nitric oxide into the blood stream, thus widening the blood vessels and lowering blood pressure.
Nitric oxide (NO) is a chemical that is important to humans. It is found in the diet in various leafy greens, like spinach, and is important in almost all organisms. NO, for example, has been shown to play a role in the immune system. Certain immune cells produce NO to help in destroying and removing foreign bacteria.
Additionally, NO plays a role in the cardiovascular system. NO is critical to the widening of the blood vessels, muscle relaxation, and the regulation of blood pressure.
Cardiovascular disease and hypertension have been shown to be related to both season and latitude. Blood pressure tends to be lower in the summer, and researchers have seen an increase in cardiovascular disease and hypertension as populations move further from the equator, suggesting an association with sun exposure.
This led researchers in the present study to speculate whether ultraviolet-A radiation (UVA) from sun exposure may help mobilize NO from storages in the skin into the blood stream. They focused on UVA because the researchers, in a previous study, found large stores of NO in the skin but had yet to discover its biological role in human health.
The researchers recruited 24 healthy volunteers to see the effects of UVA irradiation on NO. The participants were randomly assigned to two groups of 12. One group received a low nitrite/nitrate diet for 2 days before irradiation, while the other group had no dietary restrictions. All 24 volunteers received UVA irradiation.
After active irradiation with UVA, all of the participants underwent a control irradiation while wearing aluminum foil. This was to block UVA radiation from reaching the skin, to see the effects of temperature on NO and blood pressure.
The researchers then measured various markers of cardiovascular health, including blood pressure and heart rate. What kind of effect did UVA and nitrite/nitrate diet have on cardiovascular health? Here’s what the researchers found:
- There was no significant difference in mean arterial pressure between the low nitrite/nitrate diet group and the normal diet group.
- During active irradiation and for 20 minutes after, mean arterial pressure fell by 3.50 mmHg (p=0.0004).
- Diastolic blood pressure fell by 4.90 mmHg during active irradiation and was sustained for 30 minutes, while it fell by 2.79 mmHg during the control irradiation (p=0.0071).
- Their data suggest that over 80% of the NO they found to be released was caused by the UVA irradiation.
The researchers concluded,
“This study demonstrates that irradiation with UVA, corresponding to natural sunlight exposure for 30 minutes at noon on a sunny day in Southern Europe, vasodilates the arterial vasculature in NOS independent fashion and reduces blood pressure independently of changes in skin temperature. These observations support a mechanism for the modulation of systemic NO bioactivity and a possible role of the skin in cardiovascular homeostasis.”
The researchers only looked at changes in blood pressure in healthy individuals over a short period of time. Because of this, they note that they cannot say for sure if UVA maintains its efficiency on multiple exposures or how these effects would vary with age, gender or disease.
So, what is the significance of these results?
Previous studies have shown that while higher UV exposure may increase risk of skin cancer, it also helps prevent things like heart attacks and even mortality. The present study shows a potential mechanism to how sun exposure can be beneficial to our health. It shows that, on top of vitamin D production, the human body may have developed multiple mechanisms to need sunlight for various regulatory processes in the body.
In this study, researchers have shown that UVA is beneficial for NO activity. While UVB is responsible for vitamin D production, the role of UVA is less understood. It may be the case that a much wider spectrum than just UVB is responsible for maintaining good health, as this study hints at.
Larger and more experimental trials are needed to better understand the effect that the sun has on the human body.