Because I have two autoimmune conditions, my doc had vitamin D tested… my values were low. Since I’ve started taking D3 supplementation to optimal levels, I am getting much better blood sugar ranges (I have T1)
Here’s a link to the article about the studies
I haven’t had time to read your link yet but wanted to mention that for further reading there’s a good chapter in the book “Diabetes Rising” by Hurley that examines the research linking vitamin D deficiency to prevalence of both type 1 and 2 diabetes. I found it interesting.
Unfortunately, though low Vitamin D is associated with diabetes and obesity, the controlled studies done to see if raising it could affect these conditions have not shown it makes much improvement.
Also, if you supplement with Vitamin D, be sure to have your levels tested. If they get to the middle of the normal range, cut back. My endo had me supplementing at 2000 IU a day for a couple years and I ended up with damagingly high blood calcium levels, a known by-product of too much Vitamin D. High blood calcium is associated with a higher risk of heart attack as the calcium turns into arterial plaque.
D3 is the one you want to take for supplementation.
VERY important, I agree. In my own situation, the first test showed my D levels at 23–30 is the lowest normal range. However, optimal ranges from what I’ve researched are much higher than previously considered PubMed reports 75 or higher for optimal ranges.
I started on 5000mg of D3 and after 5 months tested again. I was up to 44…better but not optimal. Upon Doc’s suggestion, I increased to 10,000 in April, and now I am at 63 and feeling much, much better in all kinds of ways. 
Of course, I will continue to test values periodically. But if anyone has symptoms of low D, like insulin resistance, liver dumping, brain fog. muscle weakness and pain… or the presence of autoimmune conditions… nothing to lose in getting the labs done, right?
There are two different units used to measure Vitamon D ranges and they are confusingly similar. Using the wrong unit can mean you think you are low when you aren’t. Also the higher end of the safe range has been lowered, so older books may give bad advice.
I was still technically in the upper part of normal according to the lab reference range back when my calcium levels shot up. Middle of normal seems best.
I’m very intrigued by this conversation. So much that I started taking 2,000 IU of D3 daily. My hand surgeon also recommended taking it. He says he first discovered it’s benefits while reading about prostate and breast cancer. The majority of Americans are D deficient. So, I will take it for a while, have my levels tested and watch my bg trends.
Sarah 
That’s my understanding from the literature I’ve read as well @curlysarah . I assumed my vitamin D levels were fine because I lived in Florida for 13 years (until a couple of years ago) I had a small horse ranch and was outside in the sun every day. Of all people I “should” have had happy levels, right?
I was participating in an online summit of autoimmune condition specialists last year and heard several of them mention the high usage of vitamin D in autoimmune conditions so asked my doc to get lab values and was really very surprised at how low my level was.
Back in February of 2010 … I have online access to my script history + OCD (self diagnosed 
) … my lab tests showed my vitamin D level was low so I was started on a daily supplement of 1,000 U Cholecalciferol.
I can’t really say I have noticed any difference from taking the supplement. But what the heck, eh? I haven’t felt any worse either and maybe its making something better and I just don’t realize it? 
The Wikipedia article about Cholecalciferol starts off with the excerpt quoted below.
Cholecalciferol (toxiferol, vitamin D3) is one of the five forms of vitamin D.[1][2] It is a secosteroid, that is, a steroid molecule with one ring open.
This and all forms of vitamin D are misnamed: vitamins by definition are essential organic compounds which cannot be synthesized by the body and must be ingested; cholecalciferol is synthesized by the body, and functions as a prehormone.
Cholecalciferol is inactive: it is converted to its active form by two hydroxylations: the first in the liver, the second in the kidney, to form calcitriol, whose action is mediated by the vitamin D receptor, a nuclear receptor which regulates the synthesis of hundreds of enzymes and is present in virtually every cell in the body.
From my last lab test … also online so I could use cut’n paste … back in May of this year.
Test Name: CALCIDIOL
Result: 32
Units: ng/mL
Reference Range: 21-50
Lab Test: Vitamin D 25 Hydroxy
Interpretation:
NEW Interpretation as of 7/1/13
Vit D deficient <12 ng/mL
Vit D insufficient 12-20 ng/mL
Vit D sufficient 21-50 ng/mL
Vit D potential intoxication >50 ng/mL
OLD Interpretation prior to 7/1/13
Vit D deficient < 10 ng/mL
Vit D insufficient 10-29 ng/mL
Vit D sufficient 30-100 ng/mL
Vit D potential intoxication > 100 ng/mL
Good to see they’ve revised the upper limit!
Mine was well over 50 after the 2 years of supplementing, but since it was under 100 and it was before 2013 the endo insisted it was safe. My family doctor pointed out the high blood calcium levels were not safe. My blood pressure has never quite recovered from this episode, so do be careful!