Vitamin D has potential to combat Type 2 diabetes

Vitamin D has in studies found to be associated with a reduced risk of a range of conditions including several forms of cancer, heart disease, multiple sclerosis and ‘auto-immune’ diseases such as Type 1 diabetes, multiple sclerosis and rheumatoid arthritis. There has, in recent years, been some interest in the role that vitamin D might play in obesity and associated problems such as metabolic syndrome, insulin resistance and Type 2 diabetes.

Awhile back one of my blog posts featured some research in which women with insulin resistance were treated with vitamin D (4,000 IU) a day for six months. Insulin resistance is a state where insulin’s effects in the body are somewhat ‘numbed’, and can lead to elevated blood sugar levels (as well as other biochemical abnormalities) and may progress to Type 2 diabetes in time. In this study, compared to placebo, the vitamin D improved their insulin sensitivity, signifying likely relative protection from Type 2 diabetes.

This is just one study so I was interested to read about a recent review of the evidence as it relates to vitamin D and Type 2 diabetes [1]. Part of the review looked as epidemiological evidence which is useful for assessing relationships between things. However, just because two things are associated, that does not mean that one is causing the other. Nevertheless, the evidence from 8 studies amassed together showed that individuals with the highest vitamin D levels (>25 ng/ml = 62.5 nmol/l) had a 43 per cent reduced risk of Type 2 diabetes compared to those with the lowest levels (<14 ng/ml = 35 nmol/l).

The review also assessed intervention trials – studies in which individuals were actually treated with vitamin D (or placebo). Some of these trials were in individuals with normal insulin sensitivity and, not surprisingly, did not yield positive results (if there’s no problem, you can’t fix one, right?) Other studies were very small and therefore unlikely to detect any benefit from vitamin D that might exist.

However, in two intervention trials in individuals with evidence of insulin resistance, there was evidence of benefit in the form of improved insulin sensitivity. The authors of the review call for more high-quality epidemiological evidence, though personally I feel this would be a waste or resources. They also call for ‘randomised controlled trials’ (a form of intervention studies) in which vitamin D levels and measures of blood sugar control are assessed.

One relevant study was recently published in the American Journal of Clinical Nutrition [2], and it’s lead author was the same as the review referred to above. In this study, 92 adults deemed to be at high risk of Type 2 diabetes were treated for 16 weeks with one of the following:

  • Vitamin D (2000 IU per day) plus placebo
  • Vitamin D (2000 IU per day) plus calcium (400 mg, twice a day)
  • Calcium (400 mg, twice a day) plus placebo
  • Placebo

An interesting finding of this study was that those who took vitamin D (with or without calcium) saw significant improvement in their production of insulin. Insulin is produced by so-called ‘beta cells’ in the pancreas. The function of insulin (insulin sensitivity) was not found to be improved by vitamin D in this study. Another measure that was assessed in this study was the ‘disposition index’ – a measure which includes both beta cell functioning and insulin sensitivity. This index is believed to be a good marker for risk of Type 2 diabetes. The index improved by 26 per cent in people taking vitamin D, and worsened by 14 per cent in those who were not. All-in-all, the evidence suggests that higher vitamin D levels offers some potential in combating diabetes.


1. Mitri J, et al. Vitamin D and type 2 diabetes: a systematic review. Eur J Clin Nutr. 2011 Jul 6. doi: 10.1038/ejcn.2011.118. [Epub ahead of print]

2. Mitri J, Effects of vitamin D and calcium supplementation on pancreatic {beta} cell function, insulin sensitivity, and glycemia in adults at high risk of diabetes: the Calcium and Vitamin D for Diabetes Mellitus (CaDDM) randomized controlled trial. Am J Clin Nutr. 2011 Jun 29 [Epub ahead of print]

9 Responses to Vitamin D has potential to combat Type 2 diabetes

  1. chuck 20 July 2011 at 12:28 am #

    interesting that cholesterol is a precursor to vitamin d. statins have been shown to increase risk of diabetes. a low fat diet may also reduce cholesterol levels. low fat diets tend to be higher in carbohydrates, also a risk factor for diabetes. amazing how all this is possibly connected yet not many recognizer it.

  2. kem 20 July 2011 at 2:07 am #

    I’m a reasonably healthy and active 59 year old male and after chatting with a mate (a gp), he suggested I deal with the NZ winter as he and his family do, calciferol strong 50,000IU (PSM)… whatever that means. 1 tab a day for 10 days then 1 on the first of the month till spring. Not floating on air, but I’d guess I am flush with D.

  3. Henry Lahore 20 July 2011 at 4:05 am #

    Yes, Vitamin D both helps prevent and treat diabetes.
    Here is a summary with over 100 links to other articles on vitamin D and diabetes.

  4. DR ASHVINKUMAR BHATT 20 July 2011 at 9:31 pm #

    very true…..!!

  5. TerryJ 20 July 2011 at 9:46 pm #

    Dear Dr Briffa,

    Can you clarify what these studies mean for people who are already Type 2 diabetics rather than those ‘at high risk of developing diabetes’.

    Does taking increased amounts of Vitamin D improve things for those already Type 2 ?

    Your opinion would be appreciated. TIA.

  6. Liz Smith 22 July 2011 at 2:42 pm #

    My Danish pal with Diabetes 2 has been taking Vit D3 (encouraged by me) for over a year now. Her latest check over at the clinic produced results so good that the nurse doing the checks asked her what she was doing. She was told her blood was the best it had been in three years. Sadly she didn’t tell them about the Vit D3 – she didnt want them to say she should not take it. Seems some Doctors are a bit miffed if you take it upon yourself to add something useful to your diet. So she will never know if the Doctor would encourage any other diabetics to take it. She said she will tell them next check up if her results are still as good.

  7. Dana 23 July 2011 at 5:41 am #

    They need to look at menatetrenone next (vitamin K2, analog mk-4). It’s instrumental in the production of osteocalcin in the bones and dentin. Osteocalcin is also metabolically active and triggers fat cells to release something called adiponectin, which increases insulin sensitivity all over the body.

    Actually I pretty much consider the fat-soluble vitamins miraculous at this point. Bear in mind the real vitamins from animal sources are best–human capacity to convert the plant precursors is dubious and may have been overstated by the health authorities. Even K1 from plants doesn’t match what K2 can do.


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