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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.

New trial: Vitamin D prevents onset of type II diabetes

A new open-label trial out of Eastern India suggests vitamin D may be able to help prevent type II diabetes in those with prediabetes.

Type 2 diabetes is a condition where you have a hard time controlling sugar in your body, and you have too much glucose in your blood. Researchers are interested if vitamin D might be able to prevent or slow the onset of type 2 diabetes, because it is involved in glucose regulation a few different ways. Vitamin D might help improve pancreatic beta cell function, and it might improve sensitivity to insulin, which helps you control how much glucose you have in your blood.

However, research to date hasn’t shown a clear role for vitamin D in the prevention or treatment of diabetes.

In the current study published in the journal Diabetes Research and Clinical Practice, researchers wanted to see if vitamin D supplementation might be able to slow the onset of diabetes in prediabetic patients. Prediabetes is a transition state between normal blood glucose levels (healthy) and high blood glucose levels (diabetes), so it’s a condition where researchers can study if an intervention can prevent diabetes in shorter period of time compared to studying healthy persons.

The researchers enrolled 170 prediabetic patients aged 30-80 into their study. At baseline, if the prediabetic patient tested with a vitamin D level below 30 ng/ml, they were randomized to one of the following groups:

  • Group A, who received 60,000 IU of vitamin D once per week for 8 weeks, then 60,000 IU monthly for an average of 28 months. They also received 1,250 mg of calcium carbonate daily (equivalent to 500 mg of elemental calcium).
  • Group B, who received only calcium. They received 1,250 mg of calcium carbonate daily.

If the prediabetic patient tested with a vitamin D level greater than 30 ng/ml at baseline, they were placed in group C.

  • Group C patients also received 1,250 mg calcium carbonate daily, just like group B. They received no vitamin D.

It was an open-label trial, so all patients knew what they were taking.

The researchers followed these patients in the groups for at least one year, with a mean follow-up time for each patient of about 28 months. They did not mention what determined how long they decided to follow each patient. In their final analysis, the researchers only looked at 136 of the 170 patients, presumably because that’s how many patients lasted longer than 12 months, though again, the researchers did not specify.

They wanted to know if vitamin D helped prevent diabetes and helped with other markers of poor glucose control.

Here’s what they found:

  • Those in group A, the group that received vitamin D, had significantly lower progression to diabetes than group B. Six of 55 patients in group A developed diabetes, while 13 of 49 in group B developed diabetes (p=0.04).
  • Group A also experienced a higher incidence of reversal to normoglycemia (normal glucose levels), with 23 of 55 patients returning to normoglycemia, compared to just 10 of 49 in group B (p=0.02). In other words, patients who took vitamin D were more likely to reverse their prediabetes diagnosis and return to healthy glucose levels.
  • In group C, 6 of 32 patients progressed to diabetes and 7 of 32 patients returned to normoglycemia.
  • The vitamin D levels in group A rose from 17 ng/ml to 35 ng/ml during the study.

The researchers concluded,

“Vitamin D supplementation in individuals with prediabetes decreased progression to diabetes and increased reversal to normoglycemia associated with an improvement in insulin resistance, systemic inflammation and dyslipidemia.”

One strength of their study is that their prediabetic patients converted to diabetes at a 9% annual rate, which is consistent with previous data on Asian populations. This means that the population they studied is likely a good representation of prediabetic Asian populations. Another strength is that this study lasted for an average of 28 months and sometimes as long as 40 months depending on the patient.

A limitation is that the study was an open label trial, rather than a randomized controlled trial. So the patients knew what they were receiving and the chance of a placebo effect can’t be dismissed. Furthermore, since it was open-label, there is risk of bias from the researchers affecting the results and analysis. Another limitation is that the researchers didn’t run an intention to treat analysis, which would have meant running an additional analysis and examining all 170 patients regardless if they lasted at least 12 months.

A similar trial in the past by Davidson et al didn’t find any benefit in vitamin D in trying to prevent onset of type II diabetes in prediabetic patients, which was disappointing. One difference in the Davidson et al study however is that it only last one year. It was better quality in most other regards however because it was a randomized controlled trial.

This current study looked at a similar prediabetic population and found that vitamin D helped prevent onset of type II diabetes over the duration of an average of 28 months, which is in contrast to the findings by Davidson et al. This study should spark some hope once again that vitamin D may be an integral piece in preventing or slowing onset of type II diabetes.

Similar but much larger trials are now underway examining this issue, including the 2,500 person D2d study which we have covered before. That study will supplement patients with either placebo or 4,000 IU of vitamin D for one year. Hopefully it is long enough to see an effect. The study expects to have results by 2017.


Dutta, D., Mondal, S. A., Choudhuri, S., Maisnam, I., Hasanoor Reza, A. H., Bhattacharya, B., Mukhopadhyay, S. Vitamin-D supplementation in prediabetes reduced progression to type 2 diabetes and was associated with decreased insulin resistance and systemic inflammation: An open label randomized prospective study from Eastern India. Diabetes research and clinical practice, 2014.

  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.