Vitamin D found to improve insulin functioning

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In one of my blog posts last week I reported on a study which suggested that obesity is a potential cause of vitamin D deficiency, but that vitamin D deficiency is unlikely to have a big role in driving obesity. However, even if this conclusion is utterly correct, it does not mean that boosting vitamin D levels in the body does not benefit health, including in those who are obese.

And by way of example, just this week saw the publication of a study in which obese individuals were treated with vitamin D with good effect. The study subjects were adolescents (average age 14) with an average body mass index of about 40 (obese). They were treated with 4,000 IU (international units) of vitamin D or placebo for 6 months. Vitamin D levels in the study subjects started at about 19 ng/ml (47 nmol/l) and doubled in those taking vitamin D (no significant change in those taking placebo).

A number of parameters were measured, and here’s a brief summary of the findings:

  • Vitamin D did not affect body mass index
  • Vitamin D did not affect blood markers of inflammation
  • Vitamin D did lead to a lower level of fasting insulin levels
  • Vitamin D did lead to better functioning insulin (insulin ‘sensitivity’ was improved)

The finding that vitamin D did not affect body mass index is consistent with the recent research which suggests obesity is a potential cause of vitamin D deficiency, but not so much the other way round.

The finding that vitamin D improved insulin sensitivity is encouraging, though. In general terms, the better insulin works, the better blood sugar control is, and the lower the risk of someone developing type 2 diabetes. Proper functioning insulin basically facilitates the uptake of nutrients from the bloodstream into the body’s cells, which can improve physical and mental energy and reduce hunger.

This is only one study, but other evidence exists which shows vitamin D has the capacity to enhance insulin functioning. In one study, 4,000 IU of vitamin D given for 6 months improved insulin sensitivity in a group of insulin resistant and vitamin D-deficient women [2].


1. Belenchia AM, et al. Correcting vitamin D insufficiency improves insulin sensitivity in obese adolescents: a randomized controlled trial. AJCN. First published ahead of print February 13, 2013

2. 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. 2010;103(4):549-55

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