It is a well-known fact that sunscreen protects us against sunburn and reduces the risk of skin cancer. According to a recent study, sunscreen might also help our blood vessels maintain function. Scientists have known for many years that ultraviolet radiation (UVR) from the sun is a major causative factor in skin cancer. UVR exposure also causes cellular and molecular damage that promotes skin aging. With these two examples being well-documented, a recent study looks instead at the relationship between UVR and the performance of blood vessels in the skin. Earlier studies have shown that UVR influences how blood vessels in the skin behave. Specifically, it reduces the level of vasodilation that nitric oxide (NO) mediates. NO is an important signaling molecule in the human body. Among other roles, NO functions as a vasodilator, meaning that it triggers relaxation in the smooth muscles around blood vessels, thereby increasing blood flow. NO and vasodilation Vasodilation in the skin serves a vital role in allowing the body to maintain its temperature and respond to heat stress. If the body is overheating, NO produces vasodilation in the skin, which increases blood flow and, therefore, heat loss through the skin. Virtually every type of skin cell is capable of producing NO, but a chemical called 5-methyltetrahydrofolate (5-MTHF) is essential for this process. Experts believe that UVR reduces the levels of 5-MTHF that are available in the skin, thereby limiting vasodilation. As the authors of the current study write, NO-associated vasodilation is "a marker of skin vascular health." NO's influence may reach farther than the skin alone. Some researchers have concluded that vasodilation in the skin may have an overall effect on blood pressure. A group of scientists recently set out to investigate how using sunscreen might influence the relationship between UVR and vasodilation. They compared NO-associated vasodilation in skin that they had covered with either sunscreen or sweat. The researchers, from Pennsylvania State University, recently presented their findings at the Experimental Biology 2019 conference in Orlando, FL. Ultraviolet exposure and sunscreen To investigate, the scientists recruited 13 healthy participants with light-to-medium skin tone. They exposed one arm of each individual to UVR, while the other arm served as a control. The team calculated the UVR exposure to make it equivalent to spending roughly 1 hour outside on a sunny day. Each participant underwent three tests in parallel on their exposed arm: UVR alone, UVR plus sunscreen, and UVR plus sweat. As expected, compared with the control arm, the UVR-only test site showed reduced NO-associated vasodilation. In other words, UVR prevented NO from triggering the relaxation of the muscles in blood vessels, thereby reducing the body's ability to cool itself down. Conversely, both the sunscreen and sweat testing areas did not show a reduction in NO-associated vasodilation. Importantly, the researchers also found that when they applied sunscreen before UVR exposure, the sunscreen boosted vasodilation compared with both the sweat-tested region and the control arm. The authors write that "UVR may actually augment NO-mediated vasodilation in the presence of a chemical sunscreen." "For those who spend a lot of time working, exercising, or participating in other various activities outdoors, using sunscreen may protect not only against skin cancer but also against reductions in skin vascular function." - First author S. Tony Wolf It is important to note that this was a small-scale study that has not undergone peer review. It is also worth mentioning that, although NO is the primary regulator of vascular tone, other mechanisms play a role in this bodily function. As this experiment only assessed changes to NO-associated vasodilation, further work will be necessary to understand whether other mechanisms play a part in the interaction. However, the researchers are not attempting to overturn current recommendations. Whether or not other studies replicate their findings, using sunscreen is still as important as ever. Source
