For the study, researchers at Waseda University in Japan and Shanghai University of Sport in China looked at whether supplementing with vitamin D for a year would improve insulin resistance. They hypothesized that improved 25-hydroxyvitamin D (25[OH]D), also known as calcifediol, status after vitamin D supplementation for one year would significantly improve insulin resistance. Calcifediol is the main circulating metabolite of vitamin D3 produced in the liver. It is also the best indicator of vitamin D stores in the body. Earlier studies have shown that higher circulating 25(OH)D is associated with a lower prevalence of insulin resistance and Type 2 diabetes.
To test their hypothesis, they recruited 96 healthy Japanese adults, but only 81 completed the study. They randomly assigned the participants to take either 420 international units (IU) of vitamin D3 or placebo every day for one year. The researchers measured the participants' fasting insulin, blood sugar, and other parameters at the beginning of the study and end of the treatment. They also assessed participants' visceral fat area and physical activity.
Results revealed that supplementing with vitamin D for a year significantly increased the participants' 25(OH)D and 1,25-dihydroxyvitamin D3 (1,25[OH]2D3) or calcitriol. Calcitriol is the active form of vitamin D, usually made in the kidney. Participants who took vitamin D also saw significant reductions in fasting blood sugar levels and values of homeostasis model assessment of insulin resistance index. These were also independent of physical activity and belly fat buildup. Overall, these findings suggested that supplementing with vitamin D for a year can result in significant improvements in insulin resistance and fasting blood sugar levels. (Related: Vitamin D reduces inflammation caused by Type 2 diabetes.)
Lack of vitamin D associated with a higher risk of diabetes
A study published in the journal PLOS One has suggested that people with vitamin D deficiency may be more likely to develop diabetes. In this study, researchers at the University of California San Diego and Seoul National University looked at a cohort of 903 adults who did not have prediabetes or diabetes during clinic visits from 1997 to 1999. Then, they followed-up the participants through 2009. During these visits, they measured the participants' vitamin D levels in the blood, as well as fasting plasma glucose and oral glucose tolerance.
Over the years, 47 new cases of diabetes and 337 new cases of prediabetes were recorded. The researchers found that higher 25(OH)D concentrations – or at least 30 nanograms per milliliter (ng/ml) – were linked to lower risk for diabetes. People with vitamin D levels lower than 30 ng/ml were considered vitamin D deficient, and these people were up to five times more likely to develop diabetes compared to people with levels above 50 ng/ml.
"We found that participants with blood levels of 25-hydroxyvitamin D that were above 30 ng/ml had one-third of the risk of diabetes and those with levels above 50 ng/ml had one-fifth of the risk of developing diabetes," said first author Dr. Sue Park.
Vitamin D is an important vitamin that the body needs to function properly. Learn more about its benefits at VitaminD.news.
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