Elsevier

Nutrition Research

Volume 32, Issue 3, March 2012, Pages 195-201
Nutrition Research

Vitamin D supplementation has no effect on insulin resistance assessment in women with polycystic ovary syndrome and vitamin D deficiency

https://doi.org/10.1016/j.nutres.2012.02.001Get rights and content

Abstract

Insulin resistance is one of the most common features of polycystic ovary syndrome (PCOS). Some studies suggest that vitamin D deficiency may have a role in insulin resistance; thus, the aim of the current study was to determine the effect of vitamin D supplementation on insulin resistance in women with PCOS and a vitamin D deficiency. We hypothesized that vitamin D supplementation would lower the glucose level and insulin resistance in women with PCOS and a vitamin D deficiency. The current study was a randomized, placebo-controlled, double-blinded trial with 50 women with PCOS and a vitamin D deficiency, 20 to 40 years old, assigned to receive 3 oral treatments consisting of 50 000 IU of vitamin D3 or a placebo (1 every 20 days) for 2 months (vitamin D, n = 24; placebo, n = 26). The fasting blood glucose, insulin, 25-hydroxyvitamin D, and parathyroid hormone levels, as well as the homeostasis model assessment of insulin resistance and quantitative insulin sensitivity check index were measured at baseline and after treatment. In the vitamin D group, the serum level of 25-hydroxyvitamin D increased (6.9 ± 2.8 to 23.4 ± 6.1 ng/mL, P < .0001), and the parathyroid hormone level decreased (70.02 ± 43.04 to 50.33 ± 21.99 μIU/mL, P = .02). There were no significant changes in the placebo group. There was a significant increase in insulin secretion in the vitamin D group (P = .01), but this was not significant compared with the placebo group. The fasting serum insulin and glucose levels and the insulin sensitivity and homeostasis model assessment of insulin resistance did not change significantly by the end of the study. We were not able to demonstrate the effect of vitamin D supplementation on insulin sensitivity and insulin resistance in women with PCOS and vitamin D deficiency.

Introduction

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age. Polycystic ovary syndrome is characterized by hyperandrogenism and chronic anovulation [1]. The prevalence of PCOS in women of reproductive age is estimated to be 6.4% to 6.8% worldwide [2]. Currently, PCOS is defined by the presence of having at least 2 of the following criteria: irregular or absent ovulation, elevated levels of androgenic hormones, and enlarged ovaries containing at least 12 follicles each [3]. Of women with PCOS, 50% to 70% are insulin resistant [4]. Current evidence shows that insulin resistance has a central role in the etiology of PCOS [1]. It appears that insulin resistance and compensatory hyperinsulinemia cause hyperandrogenism [5] and obesity [6], and in addition, insulin resistance is a risk factor for impaired glucose tolerance and type 2 diabetes mellitus [7].

There is some evidence that vitamin D deficiency is related to impaired glucose clearance and insulin secretion in animal [8] and human models [9]. Vitamin D has different functions and potential effects in addition to calcium homeostasis. Vitamin D receptors exist in tissues, such as pancreatic islet cells and the ovaries. These findings show the complex effect of vitamin D on human metabolism [10]. Liu et al [11] showed that the plasma 25-hydroxyvitamin D (25 [OH] D) concentration is inversely associated with the fasting blood glucose level and insulin resistance. One recent prospective study demonstrated an inverse association between the baseline serum 25 (OH) D level and the 10-year risk for hyperglycemia and insulin resistance [12]. Pittas et al [13] confirmed that patients with impaired fasting glucose who used cholecalciferol plus calcium supplementation for 3 years had a lower increase in insulin resistance in comparison with a control group.

It has been suggested that a vitamin D deficiency is a problem in patients with PCOS [14], [15]. A recent study confirmed that increased body weight has a negative effect on serum 25 (OH) D concentrations [16], as well as parathyroid hormone (PTH) levels [17], in women with PCOS.

It should be mentioned that there have only been 2 small intervention studies with vitamin D supplementation on glucose metabolism in PCOS patients [14], [18]. With attention to the scarcity of the data on the subject, the aim of the current study was to determine the effect of oral cholecalciferol administration on insulin sensitivity and glucose metabolism indices in women with PCOS who are vitamin D deficient in a randomized, placebo-controlled, double-blinded model. We hypothesized that vitamin D supplementation would lower glucose levels and insulin resistance in women with PCOS who are vitamin D deficient. To test this hypothesis, we administered 3 doses of cholecalciferol to women with PCOS and vitamin D deficiency, and the serum glucose, insulin, PTH, and 25 (OH) D levels and insulin resistance were measured before and after supplementation.

Section snippets

Study participants

Women with PCOS were recruited from the academic outpatient clinic at Alzahra Hospital of the Tabriz University of Medical Sciences. Of 170 patients with PCOS, 60 vitamin D–deficient women were selected for the study. The sample size calculation showed that 25 subjects would be required for each arm of the trial to detect a change of 1.2 in the homeostasis model assessment of insulin resistance (HOMA-IR) with 80% power and 5% significance. The standard deviation (SD) was assumed to be 1.48 [18]

Results

Of 80 patients who met the selection criteria, 60 were accepted to participate in the study. Fifty patients completed the study (vitamin D group, n = 24; placebo group, n = 26). The details of the study design and subjects lost to follow-up are illustrated in Fig. 1.

The mean ± SD for age, BMI, and 25 (OH) D level of the 50 patients were 26.9 ± 4.2 years, 28.7 ± 4.1 kg/m2, and 7.4 ± 2.8 ng/mL, respectively. At the beginning of the study, 25 (OH) D was undetectable (<4 ng/mL) in 4 subjects (2

Discussion

In the current study, 3 oral doses of cholecalciferol (1250 μg [50 000 IU]) for 2 months did not demonstrate any improvement in insulin resistance and insulin sensitivity in women with PCOS and vitamin D deficiency. However, the HOMA-B increased significantly in the supplemented group compared with baseline, although the changes were not significant in comparison with the placebo group.

Several epidemiologic studies have shown a negative association between serum 25 (OH) D levels and

Acknowledgment

This article was written based on a dataset of MS thesis, registered in Tabriz University of Medical Sciences. The present study was funded by Nutritional Research Center (grant number: 5/71/479, 1389/5/24) and vice chancellor of research (grant number: 5/4/4151, 1389/6/4) of Tabriz University of Medical Sciences, Tabriz, Iran. There is no conflict of interest.

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