The Relationship Between Vitamin D levels and Insulin Resistance in Obese Individuals

Stephanie Budhan ’21

Figure 1. Normal insulin intake versus insulin resistance.

Obesity, or excessive weight, is often associated with insulin resistance. The hormone insulin helps decrease the body’s sugar levels. During insulin resistance, the body cells do not respond to insulin, causing the body’s sugar levels to remain high. Insulin resistance may lead to weight gain and eventually obesity.

Previous research has reported that vitamin D concentration appears to be inversely related to insulin resistance. Vitamin D may increase cells’ sensitivity to insulin through a series of mechanisms, including increasing expression of insulin receptor gene and enhancing signal transduction. However, further studies investigating the effect of Vitamin D levels on insulin resistance produced inconsistent data. A study led by Dr. Cefalo of the Catholic University of the Sacred Heart in Rome, Italy sought to determine if Vitamin D can improve insulin resistance and treat diabetes. 18 participants diagnosed with obesity (BMI greater than or equal to 30) and Vitamin D deficiency (less than Vitamin D 75 nmol/L) were utilized in the study. The researchers sought to measure a change in baseline insulin sensitivity after 3 months of dieting and Vitamin D supplementation. The study was randomized, placebo- controlled, and double- blinded.

Participants who took Vitamin D supplements combined with weight loss from dieting showed statistically significant improvement in insulin sensitivity. Furthermore, these participants displayed a loss of torso or trunk mass, an additional benefit of the increased insulin sensitivity. However, there was no significant difference between improvements in insulin sensitivity in the vitamin-D supplement group versus the placebo group. In addition, neither group showed an improvement in beta or insulin-producing cell function. Although the study was well designed, the researchers admit that the sample size was too small. Nevertheless, the data suggests that vitamin D supplementation, combined with dieting, may improve insulin sensitivity.



  1. M. Cefalo, et. al., Effect of Vitamin D Supplementation on Obesity-Induced Insulin Resistance: A Double-Blind, Randomized,Placebo-Controlled Trial. Obesity, (2018). 2018. doi:10.1002/oby.22132.  
  2. Image retrieved from:

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