Been on a sunny vacation? Got a nice tan? Think you are above the level of Vitamin D deficiency?
Yes, maybe you are, IF you tanned like described in my previous post “Do you know how to tan?”.
Unfortunately most people still adhere to the strong commercial (although hidden as medical) recommendations from makers of sun-protection lotions: ”Whenever in the sun, use lotions with high SPF and re-apply often”. If you still followed that advice, you can stop reading now because in that case you effectively prevented your skin from making any Vitamin D at all and from a health point of view, you could have saved the money for the trip to the sun.
You might have got a tanned color from the UVA-rays that most sunscreen lotions let through, but that is only a surface tan which makes your skin more dry and wrinkled and which disappears very quickly. Furthermore UVA-rays do not produce any Vitamin D. The same goes for getting a tan through a glass-window since glass lets through UVA but, just like most SPF-lotions, blocks the healthy UVB-rays that can make Vitamin D.
However, if you followed the advice in “Do you know how to tan?”, and been in the sun at a location and at a time when the sun was high enough in the sky (>50°) during a long enough time without sun-protection for your skin to make Vitamin D (but not so long that it got burned), you should have been able to considerably raise the level of Vitamin D in your blood.
When you come back home the question is how long time does it take until you again are below Vitamin D deficiency?
Many believe that a good tan during the summer keeps your level high all through the winter. Even an Authority on Vitamin D like Dr. Michael Holick, mention in his latest book “The Vitamin D Solution: A 3-Step Strategy to Cure Our Most Common Health Problem” that we can “stock up for the winter”.
Unfortunately, this “stock” of Vitamin D lasts only a couple of weeks until you again are becoming Vitamin D deficient if you don’t take any action.
I know this because I tested on myself. Arriving back after a sunny vacation to my living place (where it is impossible to get any UVB from the sun between mid-August until mid-May), my blood level of 25-vitamin D was 74.5 ng/ml (~186 nmol/l), which is a fairly safe level. (the level of deficiency varies depending on which source you read, but below 10 ng/ml (~25 nmol/l) is for sure deficient and below 30 ng/ml (~75 nmol/l) is “not enough”. More info from the Vitamin D Council here).
So far, so good. Following my own advice, I had achieved the wanted result (and, as a bonus, got a nice, long-lasting, “full-spectrum” tan). Measuring again two weeks later, the blood level of Vitamin D had already dropped to 52.7 ng/ml (~131.5 nmol/l). The sun-tan had at this time also faded to about half of what it was at arrival.
Since I don’t want to take any unnecessary risk with my health, it was then time to continue the usual habit of regular (two or three times a week) and moderate indoor solarium tanning. I know from earlier experience will keep my level of Vitamin D high enough to give a good protection towards the common colds and influenza that most other people suffer from during wintertime.
The conclusion is that, at least for me, a high blood level of Vitamin D, achieved in an optimal way to tan in the natural sun, sinks approximately at the same speed as the skin lose its tanned color. A month without “filling-up” in a solarium brings back the Vitamin D deficiency. And with that a considerably higher risk to catch any illness.