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Which type of vitamin D supplement is the safest and most effective?

Posted on: April 23, 2014   by  Niamh Aspell


Novel research published in Journal of Clinical Endocrinology and Metabolism has identified the effectiveness and differences between three forms of vitamin D3 supplements.

A multitude of evidence collected from previous clinical trials continues to support the use of dietary supplements as a safe and effective way to correct vitamin D deficiency, although the types of repletion strategies have shown great inconsistency in their effectiveness. In 2011, the Institute of Medicine published a report which emphasized the importance of evaluating the efficacy of high dose supplementation strategies.

Researchers at Bastyr University in California recently conducted a clinical trial to compare the effectiveness and differences between three different forms of vitamin D supplements in real-life routine practice conditions. The three forms of vitamin D were an emulsified oil drop (DROP), a capsule (CAP), and a chewable tablet (TAB).

They enrolled 55 healthy participants, aged 18-65 years of age, from three clinical health centers in Washington and Hawaii. Each of the three supplements were independently analyzed to measure vitamin D3 content prior to the trial and also at the end for degradation.

The 55 participants were randomized into one of three treatment groups:

  • 23 participants received DROP daily at 10,000 IU for 12 weeks.
  • 21 participants received CAP daily at 10,000 IU for 12 weeks.
  • 22 participants received TAB daily at 10,000 IU for 12 weeks.

The researchers wanted to see if there were changes in vitamin D levels between the three groups, if absorption and overall effectiveness differed between supplements, and if the labelled dosage corresponded with its actual vitamin D content.

Here’s what the researchers found:

  • All treatments were safe to administer and increased vitamin D levels significantly between baseline and 12 weeks follow up (P
  • The proportion of people who reached sufficiency was 100% for the CAP and TAB groups and 80% for the DROP group.
  • The CAP and TAB supplements both contained double the dose than what was stated on the label. Interestingly, DROP supplements were the most true to the dose claimed on the label, and it was also the most effective supplement evaluated.

The researchers were satisfied with their findings:

“We conclude that the strategy used in this PCT, dosing commercially available vitamin D₃ dietary supplements at 10,000IU/d for 12 weeks, is another safe, effective, and well tolerated strategy for clinical vitamin D₃ repletion in people with suboptimal 25(OH)D.”

This study shows that all of the three common forms of vitamin D supplementation are safe and effective at a dose of 10,000 IU/day,

Procedures need to be established and enforced to ensure standardized and independent testing of dietary supplements to make sure that the dose given on the label matches the actual dose contained in the supplement when used in research and clinical practice.


Traub ML et al. Impact of vitamin D3 dietary supplement matrix on clinical response. The Journal of Clinical Endocrinology and Metabolism, 2014.

8 Responses to Which type of vitamin D supplement is the safest and most effective?

  1. D-fiant

    Hi Niamh, thanks for your report.
    I got excited when I saw the photo at the top; I thought great, a story about the Vitamin A / Vitamin D connection. But I lucked out on that one.

    After reading the story I am still left with questions
    • Does it mean that we should buy Vit D which displays half the amount we want to take, if it is a “Cap” or “Tab” type?
    • Did the test subjects on Caps and Tabs take 20,000 IU? Or did they test these beforehand and gave them a bottle marked as 5,000 IU?
    • Did the people on Tabs and Caps reach 100% sufficiency because they were actually on 20,000 IU?
    • Of the DROP group only 80% reached sufficiency, this ‘sucks’ if you are one of the 20%. Or are we comparing a 20K intake to a 10K?
    • How does it show that all three groups are “effective” or do they mean absorption? If it is absorption – one of the three groups failed by 20%?
    • Discussing “effectiveness” this is what the whole “Vitamin D Council Site” is all about – Is vitamin D “effective” in improving our health?
    • Based on these findings it shows that the DROP type supplements have a 20% shortfall in absorption when compared to the other two forms; surely this means we should stop buying this sort? But then!, the big (and I say serious) problem with the other two types is that; how do you know what you are taking if they can be 100% in error with their content?

    I think it would have been an advantage if they also showed the average rate of daily absorption of all three types to see if the body prefers one of these types.

    Bye for now.

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  2. John Doran

    I normally recommend drops as they are the cheapest by a mile here in Ireland. I religiously check the blood levels after two months.About 20% of my clients have a poor response to the drops. When this happens I switch them to a sublingual spray which very quickly gets their levels up. It is a pity they did not test this dosage form.
    John Doran.
    Pharmacist, Naturopath, Herbalist.

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    • Mommyof3a1

      Hi. I’m intrigued by your comment here. My doctor has me on a prescription (here in the states) of 50,000 IU twice a week of D2. My levels typically run 17 in winter and 21 in summer but have been as low as 15 when not on a supplement and as high as 27 while on the supplement (prescription strength of 50,000 in a green gel capsule) and the 17-21 when using an over the counter vitamin supplement tablet. Wonder what your thoughts are? Should I ask for a liquid form, and should I be using a D3 rather than a D2? Thanks for any insight you can share.

    • IAW

      To: Mommy of Three
      You need to stop taking D2 and only take D3 it is better for you. It is also better to take Vitamin D3 on a daily basis rather than a bigger amount weekly. You did not state above how much “D3” you ever took at any one time. So start with 5000iu a day of D3 and retest your levels at 8 weeks. If that does not get you to a level of 50ng/ml, then you need to take a higher amount. (Weight does figure into how much Vitamin D3 to take.) If you raised the amount and still have no luck, then you might need to use an oral spray. There is a Q and A where you can ask more questions if you need to.

    • musiclvr56

      I was not aware that D-2 is being sold. I have only seen D-3. Also, I was told that it would take about a year for someone who takes 5,000 IU to get it to the optimum level.

  3. KGoodwin

    Is nobody concerned that these vitamin D containers are wrongly labelled? I find that shocking.

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  4. foodhospital

    D-fiant, exactly my questions.
    The abstracts reads “Participants & Intervention: 66 healthy adults with (25(OH)D) http://www.ncbi.nlm.nih.gov/pubmed/24684456
    "Label-claimed" for me would mean that participants in the CAP and the TAB arm took
    20 000 IU Vit D. The abstract does not state how the results were "adjusted".

    John Doran thank you for your information.

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  5. Rebecca Oshiro

    D-fiant, the supplement industry has little oversight and it’s anyone’s guess if any given bottle of vitamin D actually contains what the label says. For this reason it is important to purchase vitamin D (and any supplement, really) from a company that performs an assay on every batch and makes these results public. I highly recommend Biotech brand vitamin D for this reason.

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