Vitamin D supplementation found to improve insulin sensitivity

In a recent post I highlighted a study which has found that higher vitamin D levels are associated with a reduced risk of death. This evidence actually comes on the back of other studies showing the same thing, and while therefore strengthens the association between vitamin D and death risk, cannot be used to claim that increasing vitamin D levels will help prevent death. One of the points I made in this post is that what is required is randomised controlled trials which give individuals vitamin or placebo, to see if vitamin D therapy can genuinely help to prevent disease and death.

I’m generally on the look-out for randomised controlled studies, and last week reported on a review of relevant studies showing that vitamin D supplementation has the ability to help prevent falls in the elderly. This week, I’ve come across a randomised controlled study in which the effects of vitamin D supplementation were tested in a group of women suffering from insulin resistance (a precursor of type 2 diabetes) [1]. In this study, 81 women of south-Asian descent and with low vitamin D levels (less than 20 ng/ml or 50 mmol/l) were treated with 4000 IU of vitamin D3 or placebo each day for a period of 6 months.

Vitamin D supplementation caused vitamin D levels to rise from an average of 8.4 ng/ml (21 mmol/l) to 30 ng/ml (75 nmol/l).

Compared to those taking the placebo, those taking the vitamin D enjoyed improvements in insulin sensitivity and resistance (improved sensitivity and reduced resistance).

Optimal vitamin D levels were found to be between 32 and 48 ng/ml (80 – 119 nmol/l), which, according to the authors, provides further evidence for an increase in the recommended adequate levels.

The results of this study suggest quite strongly that optimising vitamin D levels may help to guard against type 2 diabetes, and this may have particular relevance for those of south Asian descent, as such individuals appear to be at heightened risk of this condition.


1. von Hurst PR, et al. Vitamin D supplementation reduces insulin resistance in South Asian women living in New Zealand who are insulin resistant and vitamin D deficient – a randomised, placebo-controlled trial. Br J Nutr 28 September 2009 [Epub ahead of print publication]

7 Responses to Vitamin D supplementation found to improve insulin sensitivity

  1. Andrea 13 October 2009 at 12:33 am #

    I was wondering what dosage of IU you recommend for a 28 yr old female. I live in Upstate, NY where in the winter months we don’t get a whole lot of sunlight. Right now I have a container of 90 pills of 2000 IU each. the directions say take one per day, but I’ve heard that in the winter females especially should have 10,000 IU. Just seems like every one says something different! What do you think?? Thanks! Andrea

  2. Ted Hutchinson 13 October 2009 at 12:38 am #

    I think we have to think hard about the phrase “Optimal vitamin D levels were found to be between 32 and 48 ng/ml (80 – 119 nmol/l), ”

    It may indeed be the case the optimal threshold for Insulin Resistance is 119nmol/l or 47.6ng/ml Everyone with levels above 120 may assume further increases in 25(OH)D will not lead to further improvements in insulin resistance.

    But it is also the case that peak muscle performance is only found to be achievable above 50ng/ml so optimal vitamin D status for athletic performance would be above 50ng/ml?.

    It’s only around 55ng/ml we find least incidence of chronic illness. So optimal status for someone wishing to avoid Breast cancer, prostate cancer, diabetes, heart disease etc would be above 55ng/ml?

    We have to raise 25(0H)D TO between 55ng~ 60ng/ml before we find optimum amounts of D3 in human breast milk. So what is optimal vitamin D status for a mother wanting to ensure her offspring enjoys a natural level of vitamin D from her breast milk?

    I’m sure the idea that the natural level of 25(OH)D the human body attains and maintains given regular full body sun exposure could not possibly have been the level our DNA evolved to work best with? Or could it?

    It would be a shame wouldn’t it if humans actually attained and maintained the 25(OH)D we evolved to naturally sustain. Goodness, a 70% reduction in heart disease, breast/prostate cancer and diabetes doesn’t bear thinking about does it, if you’re a health professional with a career and mortgage to worry about?

    I forgot to mention that correcting vitamin D deficiency isn’t the only way of improving insulin resistance. this paper shows us a higher ratio of plasma omega-6 to omega-3 fatty acids is associated with insulin resistance only in patients with metabolic syndrome and Omega-3 and omega-6 polyunsaturated fatty acids had opposing effects on insulin resistance. EPA was associated with better glucose balance, while omega-6 polyunsaturated fatty acids were associated with elevated insulin resistance.

  3. Ted Hutchinson 13 October 2009 at 2:55 am #

    Re Andrea
    Grassrootshealth D Action post25(OH)D tests world wide except for a couple of USA states where health professionals consider the residents too immature to make rational decisions about their own health.

    Unfortunately that applies to New Yorkers.

    But maybe you have an out of state friend to whom you could have a test kit mailed? Or maybe your doctor will request a 25(OH)D test on your behalf.

    Once you have donated 2 drops of blood to the sample strip and returned the envelope in the mail, a link to the results will be emailed to you in a few days. So you can then read them online.

    Without knowing your current 25(OH)D status it’s impossible to guess how much more vitamin D3 you will require to reach what you may regard as optimal.

    Assuming that at some point in the future you may become pregnant and would want to ensure your baby has vitamin D replete breast milk, a level between 55~60ng/ml would be required.

    It generally takes 1000iu to raise status a further 10ng/ml. However people with an inflammatory condition such as diabetes or celiac or heart disease may require up to 2000iu to achieve the same increase in status.

    Dr Davis of the Heartscanblog lives/works in Wisconsin and he finds generally it takes his heart disease patients 5000~6000iu/daily to achieve a level over 60ng/ml.

    So starting with a total of 5000iu daily for 3 months, a 25(OH)D test would then give you an idea of how your body responds to an effective amount of D3.

    If you are above 80ng/ml (the level naked humans usually achieve in sun) then reducing intake by 10000iu for each 10ng/ml you want to reduce that level down to 60ng/ml would be fine.

    However, if the test shows you are still significantly under 55ng/ml you would need to raise your intake a similar amount.

    Do be aware that up to 10,000iu/daily is absolutely safe even in places where vitamin d from daily UVB is available. So providing you stay under 10,000iu there will be no problems.

  4. Anna 13 October 2009 at 10:42 am #


    My parents and siblings live in upstate NY and I grew up there (Capital District), so I know well “the land where you don’t tan, you rust”. Last winter I convinced my NYS family members to get their Vit D level tested. Except for my father (who takes the Vit D in the high doses I send him every year for birthday and Father’s Day), they all tested between 13-25 ng/ml, seriously deficient. That’s 2 teenage women, one middle aged woman, and a mid-60s woman. They all thought the puny amount of Vit D in their calcium tabs, plus the 100 iu per 8 oz of non-fat milk was enough and so did their doctors. Their tests said otherwise.

    I live in “sunny” coastal San Diego and even here I have to take 5000iu day year round to keep my 25 (OH)D level above 60 ng/ml. It drops to the 40s with 2000-3000iU per day supplementation and about 40 in the summer even with with deliberate but prudent midday sun exposure I manage my sun exposure but hardly ever use sunscreen now except on for long days outdoors camping, at the beach, etc.). I’m quite sure I was very D3 deficient in my 30s and early 40s when I was actively avoiding the sun after the removal of a basal cell on my nose. Now I avoid burning, but I try to get a short but regular dose of strong midday sun. But I also supplement with D3. My husband takes 8000iu daily and our 5th grader takes 4000iu during the school year, 3000iu in the summer. We test twice a year minimally.

    In my experience with supplementing Vit D in my family (husband and son), extended family, and local as well as distant friends, it seems the Vitamin D Council’s recommendation for about 1000iu for EACH 25 pounds of body weight is a good level for many if not most people. It *is* a much higher dose than the RDA (which is much too low), but it isn’t likely to be so high as to get people in to toxicity trouble (over 200 ng/ml). I took 8000-10,000iu D3 daily for several weeks last winter to avoid the various colds and flus I was exposed to in upstate NY at holiday time (& didn’t catch any) and tested at 122 in late January. No toxicity. I just dropped the D entirely for a few weeks, then resumed my usual dose of 5000. In April I was back to 61 ng/ml. The key is to test at least once a year, preferably twice so you can find your optimal dose for the level you want. Good luck. I miss NY in the autumn.

  5. Katrina 16 October 2009 at 7:58 pm #

    I’m a type 1 diabetic and every summer my injected insulin requirement goes down. I don’t sit in the sun for long periods of time but the sun and the vitamin D definitely has a positive effect on my blood sugar levels. Roll on next summer, or I guess take a vitamin D supplement.


  1. Vitamin D has potential in combating Type 2 diabetes | Dr Briffa's Blog - A Good Look at Good Health - 19 July 2011

    […] back one of my blog posts featured some research in which women with insulin resistance were treated with vitamin D (4,000 […]

  2. Vitamin D has potential to combat Type 2 diabetes - 13 August 2011

    […] back one of my blog posts featured some research in which women with insulin resistance were treated with vitamin D (4,000 […]

Leave a Reply