A 2009 study that monitored over 8,800 elderly French adults found that an individual’s blood pressure can fluctuate with the seasons. In particular, the researchers observed that as temperatures fell, both systolic and diastolic blood pressure could rise to unhealthy levels, but they were unable to determine why.

However, a study published just five years later may have solved the mystery. The solution has to do with the molecule nitric oxide. Nitric oxide is a vasodilator, meaning that it causes the walls of blood vessels to relax and expand, with a resulting reduction in blood pressure.

Researchers have discovered that nitric oxide is stored in the dermal vasculature at levels much greater than are found circulating in the bloodstream. When exposed to long-wave ultraviolet (UVA) rays, the skin releases some of that stored nitric oxide into the bloodstream. Because individuals tend to spend less time in the sun during the winter months, there are fewer opportunities for the skin to release nitric oxide into the blood, dilate blood vessels, and moderate blood pressure. This may also help to explain why stroke and blood vessel rupture (aneurism) are more common in the winter months among the elderly.

How can one maintain healthier levels of nitric oxide in their bloodstream when it’s not convenient to spend time in the sunshine? The answers may be found in diet and exercise.

A 2018 study found that eating leafy greens and root vegetables and drinking beetroot juice effectively increased nitrate plasma (blood) levels for the purpose of enhancing exercise performance.

In 2020, researchers observed that schoolteachers in South Africa with greater physical fitness levels had higher levels of nitric oxide in their blood, as well as lower systolic and diastolic blood pressure readings. The research team concluded, “These results may suggest that even moderate physical activity could increase nitric oxide synthesis capacity, which in turn may mitigate the development of cardiovascular disease in this population.”

The take home message is that to maintain a healthier blood pressure, consider getting plenty of sunshine, eating leafy green and root vegetables (or drink beetroot juice), and exercising!