Vitamin D and tanning

I just got back from a trip to Mexico visiting beautful Playa del Carmen and had some observations about Vitamin D and tanning.

First a little background:  I started supplementing with Vitamin D3 several months ago, and undoubtedly had raised my D levels substantially before I began getting sun exposure in April of this year.  When I got out in the sun I noticed that I did not burn.  I've always tanned quickly, but had never tanned THIS quickly.

I didn't think much of it, but I did do some searching and found that other individuals on Paleo diets were reporting the same thing.  I didn't associate it with Vitamin D at the time.

Then during our trip to Mexico my older son, Charles, was relating how he couldn't seem to get a tan.  He said he had been spending almost an hour a day in the afternoon sun and just wasn't tanning.  But if he stayed out long enough, he did begin to burn.  I thought that was weird, but didn't have any idea why it would be.

My younger son, Mitch, was about as tanned (or not\ tanned!) as Charles, but by the end of the trip Mitch was much, much darker than Charles.  In the past, they've always seemed to both tan about the same.  This really got me to thinking, and then I recalled that Mitch had been supplementing with Vitamin D for several months along with me.

That experience combined with my experience earlier this year has me wondering if slow tanning rates are associated with low Vitamin D levels.  Here's my thinking:

I think that the skin darkening response is the body's attempt to not only protect itself from the sun, but also to reduce production of Vitamin D once levels are sufficient.  This paper discusses skin pigmentation of the more permanent type and how it varies with latitude.  It also explains that the production of Vitamin D decreases with increase of melanin in the skin.

I'm confident that Mitch's vitamin D levels were much higher after months of 3000-4000 IU/day of D3.  Charlie, on the other hand, had no supplementation.  And because we all participated in the same outdoor activities, I can say with certainty that our sun exposure was nearly identical.

Charlie got a slight burn but but also tanned very little.  Mitch burned less but tanned much more.  I did not burn at all but I am only slightly darker since I started very dark to begin with.  In fact, I had Mexicans ask me where I got my skin color, and jokingly asked if I was really a Mexican.  :)

So that's my theory.  I've been searching online to see if I can find support for it, but have not been successful so far.

I'll keep digging, I'm curious about this.