A tan does not equal vitamin D

The sun is getting stronger and the days are getting longer, even here in Wisconsin.

Some people are coming to the office with nice tans obtained by sunning themselves for several hours. Others have come back from winter getaways to Florida, Arizona, or the tropics, also sporting nice, dark tans.

Several people, in fact, were so confident that sunning themselves provided sufficient vitamin D that they reduced their usual dose. Some even stopped their vitamin D altogether.

But, when blood levels of 25(OH) vitamin D were checked, they were virtually all low, sometimes as low as <20 ng/ml. Yet all had nice tans.

Why does this happen? Why would people with dark tans remain deficient in vitamin D?

One big factor is age: Anyone over 40 years old is fooling themselves if they think that a tan ensures raising vitamin D levels to a desirable range. Also, the more you tan, the more melanin skin pigment accumulates, and the more vitamin D activation in the skin is blocked.

Weight is another factor: Heavier people need more vitamin D, sometimes three- or four-fold more than slender people.

Why does aging result in inefficient skin activation of vitamin D? It seems that, once we are beyond our reproductively useful years, this ticking clock of aging gets triggered. The older we get, the less activation of vitamin D occurs in our skin, the less of the youth-maintaining, disease-preventing benefits of vitamin D we obtain with sun exposure.

The message: Don't rely on a tan to gauge the adequacy of vitamin D. Maybe that works when you're 16 years old, but not at age 50 or 60. There's only one way to know your vitamin D status: a blood level of 25(OH) vitamin D.

Copyright 2008 William Davis, MD

Comments (8) -

  • Anonymous

    5/14/2008 10:03:00 AM |

    It's all about UVB exposure and amount of pigment and cholesterol in the skin.

  • ethyl d

    5/14/2008 4:36:00 PM |

    Just to clarify, I assume therefore, that, even if sunshine exposure does not guarantee adequate vitamin D levels as one ages, dietary vitamin D through D-rich foods or gel capsules do?

  • Ross

    5/14/2008 5:23:00 PM |

    Still another factor is that tanning lotions and sunscreens selectively block UVB rays, which are the higher-energy rays our bodies need to synthesize Vitamin D.  The lower-energy UVA rays that cause tanning but don't help with Vitamin D are permitted through in much higher quantities by all sunscreen chemistries.

    Like many things in this world, when we humans interfere with the natural, we tend to screw it up.  Just like we're better off with whole milk, whole eggs, whole meats (leave the skin on the chicken, it's the best part!), etc.  We also benefit most from the whole spectrum of sunlight.  Not so much that we burn, but definitely not filtered of the best and most useful components.

    If you want a tan to count towards your Vitamin D, repeatedly get outside for short periods of time without sunscreen.  I'd still recommend a supplement, since your body has all sorts of ways to manage too much, and very few ways to manage not enough.

  • Anonymous

    5/14/2008 11:32:00 PM |

    Dr. Davis, thank you for reminding us of the importance of vitamin D supplementation.   When addressing vit. D supplementation, please, we need to keep on stressing that it needs to be D3 in GEL CAPS.   There are lots of people who are hearing the vit D supplementation message, run to the drugstore and buy D tablets (often 1000 IU D2).  Their doctors and pharmacists are saying they are doing the right thing.  But from what I understand it is rather useless.  Oil based D3 in the right, larger, quantity, is what matters, because that is what the digestive system can absorb.

    Could you provide a medical research reference that clearly shows why D3 in gel caps is the only way to go?  I would like to print lots of copies to give to my friends, parents, etc....

  • Anonymous

    5/16/2008 1:11:00 PM |

    A test comparing D2 to D3:


  • Anna

    5/16/2008 6:50:00 PM |

    Check out the Vitamin D Council for a wealth of research on Vit D supplementation:  http://www.vitamindcouncil.org/

    I was so impressed with this non-profit's work that I added them to my list of charitable causes.

  • Anne

    6/9/2008 7:56:00 PM |

    Dear Dr Davis,

    I just got back from my holidays in France and am catching up with your blogs. This one interested me. I just received the results of my vitamin D test taken before I went away, the 25(OH)vitamin D3 test, and my levels are 384 nmol/L (153 ng/ml) which I understand is much, much too high.

    I am mystified at this result as I live in the UK where there isn't usually much sun and I don't sunbathe anyway and I've been taking 4,000iu D3 only since January. Obviously I am stopping the supplements right away but am very concerned.