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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

Vitamin D and T2D: Where does research stand, where are we headed?

This past November was American Diabetes Month. As many know, diabetes is becoming a major public health problem. Nearly 26 million children and adults in the United States have diabetes, with an additional 79 million Americans having prediabetes.

It is projected that one in three American adults will have diabetes in 2050, unless public health efforts successfully slow down the rising incidence rate. Currently, diabetes costs $245 billion dollars in medical care costs.

Can vitamin D help in type II diabetes (T2D)? Can it slow the rising incidence rate? Can it help prevent T2D? Can it help treat T2D?

As outlined in our T2D summary, to date, research on the effect of vitamin D on T2D has been modest. There has been no research showing vitamin D supplementation can prevent T2D. For treatment, some research shows that vitamin D helps improve insulin sensitivity and decrease insulin resistance.

However, what would really excite the T2D research field is if vitamin D could improve glucose control. To date, randomized controlled trials haven’t been able to show that vitamin D can help in this department, and thus vitamin D has failed to excite clinicians for use of vitamin D as add-on therapy in T2D.

One small trial administered 1,000 IU of vitamin D with or without calcium daily in a yogurt drink and found improved glucose control in T2D patients. Unfortunately, this has been the only study to produce such results.

Recently, researchers out of Hallym University in South Korea conducted a randomized controlled trial in attempt to yield similar results.

They recruited 158 patients to take either 2,000 IU of vitamin D or placebo each day, in addition to 200 mg of calcium daily. The trial lasted 24 weeks.

After the trial, the researchers only analyzed 65 patients in the placebo group and 64 in the vitamin D group, with 14 and 15 persons respectively excluded due to poor compliance or drop out.

After 24 weeks, the researchers wanted to know, did vitamin D help improve glucose control at all?

Here is what they found:

  • Vitamin D levels improved in the 2,000 IU group from 10.8 ng/ml at baseline to 30.2 ng/ml after 24 weeks. In the placebo group, vitamin D levels rose a little, too, from 10.1 ng/ml to 15.6 ng/ml.
  • There was no difference in glucose control between the vitamin D and control group after 24 weeks, as measured by hemoglobin A1c (HbA1c). HbA1c percentage after 24 weeks was 7.40 in the vitamin D group and 7.27 in the placebo group (p=0.415). There was also no difference in change in HbA1c from baseline to 24 weeks between the two groups.
  • Somewhat surprisingly, there was also no difference in insulin resistance after 24 weeks either, as measured by the homeostasis model of assessment-insulin resistance (HOMA-IR). HOMA-IR was 2.1 in both groups at the end of the trial (and the change in HOMA-IR from baseline was not significantly different between the two groups).

The researchers concluded, “This trial shows that use of high-dose vitamin D has no meaningful effect on long-term glucose control and IR in patients with T2DM.”

So is this the end for vitamin D and T2D research?

No. The researchers note that we need longer trials with higher doses of vitamin D to really be able to discern whether vitamin D can help in T2D. Such trials are underway.

One study is the D2d study out of Tufts Medical Center that is being funded by the NIH. They will administer 4,000 IU of vitamin D/day or placebo for up to four years to see if vitamin D can help prevent T2D in those with prediabetes (a clinical term for those at high risk of developing T2D).

Another study that may provide good data on vitamin D and T2D is the well-known VITAL study that is administering 2,000 IU of vitamin D/day or placebo to 20,000 Americans for about five years. They should be able to see if there is a difference in how many develop T2D over the five year period and if there are any differences in incidence between the vitamin D and placebo group.

If vitamin D proves to be effective in these larger and longer trials, then we can more definitively say that vitamin D can help with glucose control. If so, the studies would imply that vitamin D needs to be taken for many years to see any appreciable effect. Until then, vitamin D’s role in T2D remains unclear and puzzling.


Ryu OH et al. A prospective randomized controlled trial of the effects of vitamin D supplementation on long-term glycemic control in type 2 diabetes mellitus of Korea. Endocrine Journal , 2013

  About: Brant Cebulla

Brant Cebulla was a staff member for the Vitamin D Council from May 2011 to April 2014. He has keen interests in nutrition and exercise.

3 Responses to Vitamin D and T2D: Where does research stand, where are we headed?

  1. There is another aspect of these studies that need to be considered. 2000iu is often called high dose. It is hardly a high dose by definition today. My wife and I are taking over 5000iu daily and our blood levels are between 50 and 60 ng/ml. both of us have experienced major improvement in knee pain. This was not the case when we were taking 2000iu with blood levels in the high 30s and low 40s. And it also was not an expected outcome for us. A randomized study published in June using 2000iu found no significant reduction in pain by vitamin D supplementing. While our experience is not scientific, it certainly presents the possibility that blood levels matter. It could be that different levels could affect diseases differently which will certainly complicate accessing the value of vitamin D.

  2. Brant Cebulla says:

    tierrainc@email.com, very fair argument in that we need to make sure that people are getting big enough doses to see an effect.

    There was a trial published earlier this year that I think most here would argue was very well designed:

    Davidson MB, Duran P, Lee ML, Friedman TC. High-dose vitamin D supplementation in people with prediabetes and hypovitaminosis D. Diabetes Care. 2013 Feb;36(2):260-6. doi: 10.2337/dc12-1204. Epub 2012 Oct 1. PubMed PMID: 23033239; PubMed Central PMCID: PMC3554269.

    The researchers administered titrated vitamin D doses to patients with pre-diabetes to ensure that all patients in the vitamin D group had a vitamin D level of about 70 ng/ml by the end of the trial. They wanted to know if these blood levels protected against development of diabetes compared to placebo (blood levels of about 20-25 ng/ml). After a year, there was no effect of having higher vitamin D levels on risk of developing diabetes.

    Hopefully longer trials will prove differently.

  3. IAW says:

    So I went to the above cited article by Brant titled “High-dose vitamin D supplementation in people with prediabetes and hypovitaminosis D. Diabetes Care”. Brant said “that I think most here would argue was very well designed”.

    It says in the results that “At 12 months, A1C levels were significantly slightly less (0.2%) in the vitamin D group.” They used the word “significantly”.

    At one point a while ago I was looking up A1C and came across this article ” The Pros and Cons of Diagnosing Diabetes With A1C” by Enzo Bonora, MD, PHD1⇓ and Jaakko Tuomilehto, MD, MA, PHD2. There seem to be an awful lot of “cons” for using the test.
    So I am neither a doctor or scientist but I am not sure if the A1C measurement was a good way to go to determine anything. Maybe a lot of people were included as pre diabetic that really are not. Maybe there is another factor(s).