A High Dose, Not Low Dose, of Vitamin D Ameliorates Insulin Resistance in Saudi Women

Abstract

Vitamin D has been traditionally seen to be mainly involved in the regulation of bone homeostasis. However, vitamin D has also been clinically linked to various diseases, including metabolic syndrome. The aim of this study was to examine the effect of low and high doses of a vitamin D supplement on the serum levels of 25(OH)D3 and insulin resistance. A total of 120 females were recruited in this study and supplemented weekly with 25,000 IU vitamin D or 50,000 IU vitamin D for three months. Anthropometric measurements were taken at the beginning of the study. Blood samples were collected at the beginning of the study to determine the baseline of the clinical variables and collected again after three months. Insulin resistance was measured using Homeostatic Model Assessment for Insulin Resistance (HOMA-IR). After vitamin D supplementation, a non-significant increase was observed in the serum levels of 25(OH)D3 in the group treated with a low dose of vitamin D (LDVD) and a highly significant increase was seen in the group treated with a high dose of vitamin D (HDVD). In the group treated with a higher dose (HDVD), a significant improvement in insulin sensitivity was observed. The high dose of vitamin D (50,000 IU) supplementation was more effective in both correcting the blood levels of vitamin D and improving the sensitivity of insulin.

Keywords: 25(OH)D3; body mass index; insulin; insulin resistance; type 2 diabetes; vitamin D deficiency.

Figure 1

Veil style, duration, and time of sun exposure for all participants.

Figure 1

Veil style, duration, and time of sun exposure for all participants.

Figure 2

Comparison of fasting serum levels of 25(OH)D3, Ca, and PTH. Comparison was carried out between LDVD and HDVD groups and their levels before (B) and after (A) treatment of the same group using two-way analysis of variance followed by Tukey’s multiple comparison test. Bars represent the serum concentration of biochemical variable. Error bars represent standard error of the mean (SEM). Exact p-values are recorded on graphs. Data were considered significant if p < 0.05. *** p < 0.001.

Figure 3

Comparison of measurements of glucose, insulin and HOMA-IR. Comparison was carried out between LDVD and HDVD groups and their levels before (B) and after (A) treatment of the same group using two-way analysis of variance followed by Tukey’s multiple comparison test. Bars represent the serum concentration of the biochemical variable. Error bars represent standard error of the mean (SEM). Exact p-values are recorded on graphs. Data were considered significant if p < 0.05. ** p < 0.01, *** p < 0.001.

Figure 4

Inverse correlation between serum 25(OH)D3, insulin, and HOMA-IR in LDVD and HDVD group before (B) and after (A) three months of vitamin D supplementation (50,000 IU).