High blood pressure is one of the most common medical conditions worldwide. It is a risk factor for heart disease, stroke and kidney failure.
Research over the past 20 years suggests that high blood pressure may be, in part, responsive to the sunlight. That is to say that regular sun exposure may help to reduce high blood pressure by stimulating the skin to reduce a compound called nitric oxide.
Nitric oxide is a very important chemical found in many manufacturing processes. Even thunderstorms produce large amounts of nitric oxide. In humans, nitric oxide is important because it acts as a signaling molecule for a number of metabolic processes, especially those linked with blood pressure.
Basically, increased levels of nitric oxide lead to the dilation of blood vessels, ultimately resulting in lower blood pressure. One of the first medications used for patients experiencing chest pain from a heart attack is nitroglycerin. Although not as popular as it once was, this medication is still used today to dilate blood vessels in an emergency.
Patients with heart disease and high blood pressure often have measurable deficiencies in their ability to make nitric oxide. Indeed, nitric oxide is so important that it in 1992, the scientific journal Science declared it to be the "Molecule of the Year."
One frequency of sunlight called ultraviolet A (UVA) stimulates the release of nitric oxide from our skin. There are three frequencies of sunlight that are commonly referred to -- UVA, UVB and UVC.
UVA light has the lowest frequency. However it penetrates the deepest into the skin, but has the weakest risk for skin cancer. It is the UVA frequency of light that stimulates the release of nitric oxide.
What is the evidence that UVA light exposure has a clinical benefit for high blood pressure?
There are a number of diseases that are associated with latitude. Heading north from the equator, the incidence of these diseases increases. Among these are high blood pressure, heart disease, diabetes, autoimmune disease and osteoporosis. This suggests that exposure to sunlight may reduce the incidence of these diseases.
We already know that vitamin D levels diminish as latitude increases. This is part of the basis of vitamin D supplementation.
A recent medical study (2014) in the Journal of Investigative Dermatology demonstrated that nitric oxide produced locally in the skin as a result of UVA exposure lowered blood pressure. This effect was independent of vitamin D, as well as independent of any food that could increase nitric oxide levels.
Twenty-four participants were exposed to modest levels of UVA light. All had reductions in blood pressure correlating with increases in nitric oxide levels.
Although this study is quite recent, the relationship between UVA light and the production of nitric oxide in the skin has been studied for decades.
• Patrick B. Massey, M.D., Ph.D is medical director for complementary and alternative medicine for the Alexian Brothers Hospital Network and president of ALT-MED Medical and Physical Therapy, 1544 Nerge Road in Elk Grove Village. His website is www.alt-med.org.