Some basic vitamin D issues

The last post on vitamin D raised a number of basic questions among readers. So let me discuss some of these questions one by one. All of them raise important issues surrounding the practical aspects of managing vitamin D in your health.

Anne said:

I think it is important to stress that vitamin D supplementation needs to be continued long term.

I have met too many people who have been prescribed 50,000 IU of D2 for 8-12 weeks and then told to stop because their 23(OH)D went over 30ng/ml. I know one person who's doctor stopped and started the D2 3 times.

Thanks for pointing that out, Anne. Excellent point. I also see doctors do this with statin drugs: start it, check a LDL level which is lower, then think that you're done and stop the drug. What the heck are they thinking?

If vitamin D is not being produced by sun exposure and not obtainable through diet, continued supplementation is necessary, essentially for life.

Twinb asked:

How often you think Vit. D levels should be tested after the initial test is done, especially if the levels are drastically low?

We have used every 6 months in the office. Ideally, levels are in mid-summer and mid- to-late winter in order to gauge the extremes of your seasonal fluctuations. While most adults over 40 fail to fluctuate more than 10 ng/ml in the Wisconsin climate (and this summer, after an initial rainy season early, has been flawlessly bright and sunny, in the high-70s and 80s every single day for months), an occasional person fluctuates more widely. The only way to judge is to check a blood level.

Rich said:

Vitamin D dosage effects appear to be quite idiosyncratic.

Yes, indeed it is. Despite using crude rules-of-thumb, like taking 1000 units of vitamin D per 10 ng/ml desired (a rule I learned from Dr. John Cannell, which he offered fully aware of its inaccuracy), many people will surprise you and have levels that make no sense. Testing is crucial to know your vitamin D level.

Richard asked: Where do we get enough vitamin D wihout worring about laboratory tests?

Well, the entire point of the post was that you absolutely, positively cannot just take vitamin D blindly at any dose and hope that your level is ideal, no more than you can blindly take a dose of thyroid and know you have achieved normal thyroid levels. In my view, vitamin D blood levels are an absolute.

Another simple issue: Don't be afraid of vitamin D. It is, in all practicality, no more dangerous than getting a dark tan. (But, as many of you realize, getting a tan is no assurance of raising vitamin D if you are over 40 years old.)

Wouldn't it be great if someone developed a do-it-yourself-at-home skin test for vitamin D? I know of no effort to develop this, but it would be a huge advantage for all of us.

Comments (7) -

  • Anne

    8/24/2008 2:06:00 PM |

    Ted wrote "I am a 64yr old male living in the UK. My skin is fairly tanned as I try to get as much full body sun exposure as is available here however I have also been taking 5000iu/daily for a couple of years now. When I was last tested my score was 147.5nmol/l 59ng/ml. I wonder if Anne's numbers are the result of a faulty test."

    I said to my endocrinologist that I thought the high test result I had, 384 nmol/L (153 ng/ml), was a lab error, but he was pretty sure it was correct. Maybe it's because I'm slim and can't store the D3 easily so I'll gain serum levels of it easily and lose it equally easily ? I contacted Dr Reinhold Vieth who has done a lot of research into D and he suggested I could have a hypersensitivity to D - if so, this will become apparent when I have my next test.


  • Anonymous

    8/24/2008 7:32:00 PM |

    Great post

    If you have been taking 4000iu D3 daily for several months and then suddenly stop taking any, after a week would depression and lethargy be a side effect?


  • rabagley

    8/25/2008 4:14:00 AM |

    The most important thing to realize about Vitamin D is that your body has many ways to deal with excess quantities, and almost no way to deal with a deficiency.

    Once 25(OH)D gets above ~80ng/ml (which takes a LOT of vitamin D over a long period of time), your body begins to store Vitamin D in your fat cells.  The amount that can be safely stored in your fat is almost an order of magnitude larger than what is carried in your blood serum (equivalent of 500-600 ng/ml).  It takes a truly ridiculous amount of Vitamin D3 taken for a long time to saturate your fatty tissue.

    If you have sarcoidosis, which often causes problems with conversion of Vitamin D active forms in your body, supplemented Vitamin D will probably make your condition worse.  For everyone else, it is extraordinarily hard to overdose on oral Vitamin D supplementation.

    40,000 IU's/day for a month might cause problems for a normal person, but almost nobody will recommend more than 10,000 IU's/day (the same amount a young person's skin can make in 30 minutes of low-latitude, noonday sun).  Another number to be aware of is 4000 IU/day, which is the amount of Vitamin D that an average human body with normal levels of 25(OH)D will use up in a day.

    The RDA (at 400 IU's/day) is based on old science.  Completely ignore that number as worthless and dangerously out of date.  That amount will stop rickets and little else.  That's little help for bones, for cancer prevention, for steering calcium away from arterial walls, for all of the other things that Vitamin D will do in your body.

  • Anonymous

    8/25/2008 10:16:00 AM |

    I'm familiar with a couple chemists that tried to make a Vit.D home testing kit.  They looked up older TLC methods for making a Dkit that was similar to the home cholesterol kits.  They spent time on it, and  felt they had a result on one of the tests, but in the end decided it was going to take too much time to do right.  More time than they could offer, so the project was shelved.

  • moblogs

    8/25/2008 10:50:00 AM |

    Because I'm not ill I'm only really allowed vit D tests yearly (I would probably be seen as an NHS pest if I pursued it), but I'm taking 5000IU for the last year to see what this does to my unsupplemented level of 10nmol/L. I was prescribed 400IU and that only raised me by 11nmol/L to 21nmol/L, so in understanding the relative safeness of D, and how other family members respond to it (almost always needing higher), I don't feel like I'm playing Russian Roulette. I'm allowed a blood test late September though.

  • Anonymous

    8/26/2008 3:33:00 PM |

    This could be grist for another post (along the lines of how disastrously low the US RDA is for Vit. D):

  • Anonymous

    9/1/2008 6:01:00 PM |

    Dr Davis,

    Have you watched this video on vitamin D?