How long prior to Vit D & B12 test should I stop taking these supplements?

I plan to get my Vitamin D & B-12 levels checked soon. They were last checked 20 months ago, and I have been taking oral Vit D & sublingual B-12 pretty regularly ever since. I recall that I need to stop taking these supplements at some point prior to getting tested so that the test results will reflect the actual level in my body, not the amount I just deposited into my bloodstream that morning from a supplement. Is that true? If so, how long do I need to go without Vit D and B-12 for my blood test to be accurate? A day? A week?

10 Replies

  • How long what we take remains in our system is generally measured by the 'half life', i.e. how long it takes before half of what we've taken remains in our bodies. It takes twice that period for a quarter to remain, three times for an eighth to remain and so on.

    The half life of vitamin D is quoted at about 3 weeks. Vitamin B12 is much more slowly used. According to Wikipedia, it can take up to a year for a deficiency to show:

    So if you are trying to determine your levels based on your diet without supplementation, you'd need to wait at least a month for vitamin D and much longer for B12 - assuming your body wasn't using much higher than normal amounts of these vitamins due to CLL...


  • Hmmmm. I would not want to stop either for a month, let alone longer. I feel I am getting a lot of benefit from each. Yet it would also be nice to get an accurate measure of what my levels are. Conundrum.

  • There is no need to stop...taking vitamins...most testing like Schilling test, MMA etc are looking at other reasons for B12 deficiency like malabsorption.

    The common VitD3, test is 25(OH)D I get it every 6 months and have for years, never told to hold the D3...

    By the way, your province no longer pays for Vitamin D testing, it a $30 charge... last time I had it run... There is a special group who can get paid tests, but CLL is not included.


  • Chris responded exactly as I was about to reply and with considerably more information. If you are benefiting from supplements, it's more a point of finding whether the dose you are taking is maintaining levels within the normal range - while not causing any problems for your liver or kidneys, etc.


  • good point neil! I will ask for liver function tests. & kidney


  • I agree the more relevant answer is your levels with supplements so you can then modify if necessary. Query whether taking them the day of or before somehow bumps up the results too much. Maybe dont take them the day of the test? I needed over 5000 of D3 daily to get my levels to 70 or above.

  • thanks. yes, i will ask the lab or doctor. and will at least have labs done before taking vit d that day.

  • This is the initial test you want. Then if deficient you go from there...

    There are about 6 different additional tests, and they may run others if anemia is a concern.

  • I was tested every three months while finding the right dose to get and keep me at a good level - now around every 6 months. I have never been told to stop taking the pills before a test. They need to know where you are so they can figure out whether you need anything adjusted. It took adjusting up to get my Do to move and then to settle on an ongoing dose. My B12 shot up and getting that dose right was an up and down process.

  • thanks for the info.

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