Health industry

The D2d Trial: Can Vitamin D Prevent Diabetes?

Scientists in America are undertaking a national clinical trial to investigate if Vitamin D can help to delay, or even prevent, type 2 diabetes.

Over the last few years evidence has come to light that Vitamin D supplements may prevent the development of type 2 diabetes. In the UK, there are 2.9 million people affected by diabetes and 90% of them have type 2 diabetes; this type of diabetes is caused when the body produces insufficient insulin to reduce blood sugar levels, or when cells no longer respond to the insulin being produced. Furthermore, by 2025 it is predicted that five millions people will have diabetes as our population continues to put on weight; making this disease one of the biggest health challenges in the UK today. If the vitamin D and type 2 diabetes (D2d) clinical trial demonstrates that this supplement can help control this disease it would significantly impact on millions of lives worldwide and help save money on medical treatment 1.
The study is being lead by Professor Philip Raskin at the University of Texas Southwestern Medical Centre, and will take 4 years as it follows the progress 2,500 clinical trial participants with prediabetes. Prediabetics have higher than normal blood glucose levels, and are at risk of developing diabetes in the future. This will be the first trial of its kind and builds on findings that suggest low vitamin D levels are correlated with higher risk of type 2 diabetes. Studies have demonstrated that vitamin D levels decrease with age, obesity and in Black and South Asian populations; groups which are at risk of developing type 2 diabetes. Type 1 diabetes may also be linked to vitamin D as risk of type 1 diabetes is higher at increasing latitudes where there is less sunlight and greater chance of vitamin D deficiency.

A high dose to see effects

Researchers in Texas speculate that vitamin D supplements may act to decrease the risk of developing diabetes by 25%, one of the ways it may do so is by improving insulin sensitivity 2-3. The D2d trial will involve giving half the trial participants a daily dose of 4,000 IU of Vitamin D3 (cholecalciferon) – for more information on the different types of Vitamin D see our infographic 4. This is much higher than the recommended daily dose of vitamin D in the US which stands at 600-800 IU (15-20 micrograms) but is still reported as within safe limits.
Currently the UK Department of Health recommends that:
  • all pregnant and breastfeeding women should take a daily supplement containing 10 micrograms (0.01mg or 400IU) of vitamin D to ensure the mother’s requirements for vitamin D are met and to build adequate foetal stores for early infancy
  • all babies and young children aged six months to five years should take a daily supplement containing vitamin D in the form of vitamin drops to help them meet the requirement set for this age group of 7-8.5 micrograms (0.007-0.0085mg or 280-340IU) of vitamin D a day
  • babies fed infant formula will not need vitamin drops until they are receiving less than 500ml (about a pint) of infant formula a day, as these products are fortified with vitamin D
  • breastfed infants may need to receive drops containing vitamin D from one month of age if their mother has not taken vitamin D supplements throughout pregnancy
  • people aged 65 years and over and people not exposed to much sun should also take a daily supplement containing 10 micrograms (0.01mg or 400IU) of vitamin D 5

Vitamin D supplements in other diseases

A recent analysis of all the research into the role of vitamin D on bone density reported that vitamin D had no significant effect when taking 800 IU or less per day 6. But, whilst we are still advised not to exceed 1000 IU/ 25 micrograms a day, it has been suggested that supplementation with <800 IU may be insufficient to see the full beneficial effect of vitamin D on bone health. Furthermore, the recommended supplement level in the UK of 400 IU/day has been criticised by experts at the Barts and The London research centre who suggest a supplement of up to 5000 IU a day may be required to prevent rickets 7 and there is evidence that a short course of high dose vitamin D may be required to correct vitamin D deficiency 8.

Whilst the media was quick to pick up on the negative finding of this analysis, suggesting vitamin D supplements “do not help bone health” 9, the results could suggest that a combination of calcium and vitamin D supplementation is required to increase bone density in health adults, alternatively vitamin D supplementation may only improve the bone health of those with osteoporosis or over the age of 65. However, as highlighted in the last blog post, we do know that chronic vitamin D deficiency can significantly affect our bone health and only time will tell if vitamin D might also help to prevent diabetes.

Final remarks

As vitamin D can be toxic at high doses, particularly when taken over a long period of time, it is important that we don’t exceed recommended doses. The current discussion around what levels of vitamin D supplementation should be recommended suggests that we still have much to learn about vitamin D’s role in our health. It also highlights the need for personalised medicine and advice to ensure that every individual is being treated for their circumstances.
1. number NCT01942694

2. Belechia, AM 2013 – as NCT00994396
3. Talaei, A 2013 The effect of vitamin D on insulin resistance in patients with type 2 diabetes

6. Reed, IR 2013 Effect of vitamin D supplements on bone mineral density: a systematic review and meta-analysis.
8. Vincent, P 2011 An effective high dose supplelemt protocol for hypovitaminosis D

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