Believe it or not, the effects of sunscreen application on vitamin D production are not fully understood. In the past, some studies show that sunscreen blocks all production, while others show that a little bit of vitamin D can still be produced. Last month, a team of researchers clarified the confusion.
The researchers, led by Professor Annesofie Faurschou, theorized that sunscreen thickness determines whether you can produce vitamin D or not, and based on the thickness, determines how much you produce. So they set up a randomized controlled trial to find out.
Faurschou A, Beyer DM, Schmedes A, Bogh MK, Philipsen PA and Wulf HC. The relation between sunscreen layer thickness and vitamin D production after UVB exposure – a randomised clinical trial. British Journal of Dermatology, 2012.
The investigators recruited 37 healthy participants between the ages of 18 and 49, all with skin types between very fair and creamy white. The participants were then randomized to apply sunscreen in layers of 0 mg/cm², 0.5 mg/cm², 1.0 mg/cm², 1.5 mg/cm² or 2.0 mg/cm² to approximately 25% of their body. They used SPF 8.
After the participants applied sunscreen, they waited 20 minutes before exposing themselves to UV via florescent tubes. The researchers gave every participant a UV dose of 3 SEDs (enough UV exposure to produce a slight pinkness to the skin in most skin types). This exposure was only applied to the 25% of skin that was covered by sunscreen.
This procedure was repeated four times, with 2-3 day intervals between each visit. The researchers measured 25(OH)D levels at baseline and then three days after the participants’ last visit. The results are displayed in the table on the right.
As you can see, the increase in vitamin D levels shows exponential growth the thinner the sunscreen application. There is a fourfold difference between applying 2 mg/cm² and no sunscreen at all. Even a small layer of sunscreen at 0.5 mg/cm² produced half the increase in vitamin D compared to no sunscreen.
The Vitamin D Council recommends a balanced and sensible approach to sun exposure, taking into consideration both vitamin D production and protection from burning. With all this in mind, on a sunny day, we recommend exposing yourself for half the time it takes to turn pink, and then covering up, preferably with clothing or shade.
If you must use sunscreen to protect your skin from UV exposure, you should slather the sunscreen on in large quantities. This study shows that since vitamin D production is compromised by at least twofold, if not fourfold, no matter the thickness, you might as well focus on protecting your skin, rather than trying to protect your skin and produce vitamin D simultaneously.