In that low circulating levels of Vitamin D [measured as serum 25-hydroxyvitamin D (25(OH)D] have been shown to correlate with an increased risk of type-2 diabetes, a study by New Zealand researchers investigated the role of Vitamin D supplementation to improve insulin resistance and insulin secretion.  Pamela R. von Hurst, from Massey University (Auckland, New Zealand), and colleagues studied 81 South Asian women with insulin resistance, ages 23 to 68 years, living in New Zealand.  The study participants were randomly assigned to receive either 100 micrograms (4,000 IU) of Vitamin D3 or placebo daily for six months.  In those women receiving Vitamin D supplementation, the researchers found insulin resistance to be markedly lower, the optimal effects achieved when blood vitamin D levels were in the range of 80 to 119 nanomoles per liter.  The team concludes that: “In conclusion, improving vitamin D status in insulin resistant women resulted in improved [insulin resistance] and sensitivity … providing further evidence for an increase in the recommended adequate levels.”