The double-blinded, placebo-controlled clinical trial started by giving 20 test subjects a small UV-lamp-delivered sunburn on their inner arm. Within one hour, they were then given either a placebo pill, or 50,000, 100,000, or 200,000 IU of vitamin D. Their skin was subsequently analyzed 24, 48, 72 hours and one week after the experiment.

While the placebo and the lower doses had little to no effect, the higher doses significantly reduced inflammation and redness, plus the test subjects experienced a jump in gene activity related to skin barrier repair. The scientists believe this was because vitamin D increases levels of an enzyme known as arginase-1, which both boosts tissue repair and activates anti-inflammatory proteins.

That said, the effective doses in the experiment were far above the 400-IU daily recommended allowance of vitamin D. 

"I would not recommend at this moment that people start taking vitamin D after sunburn based on this study alone," says lead scientist Dr. Kurt Lu. "But, the results are promising and worthy of further study."