Vitamin D fails to prevent Type 2 Diabetes (unaware of 8 proven ways)
Vitamin D fails to prevent type 2 diabetes in large study
The actual study $40 million
Note: Diabetes and pre-diabetes are associated with poor guts
Since the start of this trial (2013) there have been many proven ways to deal with the restrictions of a poor gut
1) Use the same total amount of Vitamin D, but less frequently - the higher gradient gets thru better
2) Use more vitamin D daily
3) Use a probiotic to deal with the gut problem
4) Use a gut-friendly form of Vitamin D - there are more than a dozen types
5) Increase the response to Vitamin D by using Omega-3 and/or Magnesium
Avoid the poor gut
6) Use an injection
7) Use UV or sun
8) Use topical Vitamin D
The current failed trial was probably unaware of any of the above proven solutions
4,000 IU orally daily, no probiotic, no Magnesium, no Omega-3
Note: The pre-diabetic subgroup which started with < 12 ng of Vitamin D were 62% less likely to get diabetes
See also VitaminDWiki
Non daily
Prediabetes both prevented and treated by monthly Vitamin D, etc.
Insulin resistance helped with 50000 IU of vitamin D weekly – Feb 2013
Type 1 diabetes helped with 50,000 IU of vitamin D every two weeks – Nov 2014
Better than Daily category listing has items along with related searches
Probiotic
Vitamin D treatment of diabetes (50,000 IU every 2 weeks) augmented by probiotic – RCT June 2018
Not oral
Vitamin D injection is far better than oral for diabetics (poor gut) – RCT March 2017
Diabetes treated if given enough vitamin D (example: 50,000 IU weekly) – review of RCT - Jan 2017
Omega-3, Mg, etc
Magnesium is associated with prevention and treatment of Diabetes – Meta-analysis Aug 2016
Getting Vitamin D into your blood and cells has the following chart

Getting Vitamin D into your blood and cells has a section on poor digestion
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Titles of some of the web reports of this study
NIH-Funded Trial Finds Vitamin D Does Not Prevent Type 2 Diabetes In People At High Risk
Vitamin D3 Supplementation Fails to Significantly Lower Diabetes Risk in Patients with Pre-diabetes
D2d — No Defense against Diabetes
NIH-funded trial finds vitamin D does not prevent type 2 diabetes in people at high risk
D2d: Vitamin D Doesn't Stop Diabetes in Those With Prediabetes
Maine Researcher: ‘Excess Enthusiasm’ For Vitamin D Tamped Down By New Study
Vitamin D Supplements Don't Lower Type 2 Diabetes Risk, Study Suggests
Vitamin D Doesn't Halts The Progression Of Type 2 Diabetes In Patients With Prediabetes
Vitamin D Supplements Do Not Reduce Type 2 Diabetes Risk Significantly
Vitamin D Supplementation Did Not Prevent Type 2 Diabetes in Large Trial
Vitamin D does not prevent type 2 diabetes in people at high risk