Every year, Richard Weller spends time working in a skin hospital in Addis Ababa, Ethiopia. Not only is Addis Ababa near the equator, it also sits above 7,500 feet, so it receives massive UV radiation. Despite that, says Weller, “I have not seen a skin cancer. And yet Africans in Britain and America are told to avoid the sun.”

It's not hard to google "cancer in Ethiopia" and find evidence better than one eyewitness. It is hard to find information about cancer in Ethiopia that doesn't mention skin cancer.

One review of 919 patients with biopsy-confirmed cancers at Tikur Anbessa Hospital in Ethiopia found 15 skin cancers among male patients, the same number as prostate cancers (but the skin cancer patients were 20 years younger on average). The number of female patients was similar.

It was already well established that rates of high blood pressure, heart disease, stroke, and overall mortality all rise the farther you get from the sunny equator, and they all rise in the darker months. Weller put two and two together and had what he calls his “eureka moment”: Could exposing skin to sunlight lower blood pressure?

Sure enough, when he exposed volunteers to the equivalent of 30 minutes of summer sunlight without sunscreen, their nitric oxide levels went up and their blood pressure went down.

Would have been nice if he asked half the volunteers to use sunscreen (and the other half a similar non-sunblock lotion) so he could actually gather evidence on his theory.

Weller’s largest study yet is due to be published later in 2019.

Does Incident Solar Ultraviolet Radiation Lower Blood Pressure?

Weller got data from 342,457 dialysis patients over three years and found that "in addition to environmental temperature, incident solar UV radiation is associated with lower SBP [systolic blood pressure]."

UV exposure was estimated with public weather records for dialysis locations, with no individual data about behavior or sunscreen use among the patients.

Regional variations of blood pressure could have many causes: genetic disposition of local populations, body weight, physical activity patterns, diet (including salt), and psychosocial stress.

A dermatologist reviewed the article and a study showing that "women with active sunlight exposure habits experience a lower mortality rate." The mortality benefit is due to cardiovascular health which outweighs an increased risk of skin cancer. The dermatologist points out that the researchers "did not control for several other important confounding factors in this study. Sun protective measures, for one!"