New research sheds light on the interaction of vitamin D levels and insulin.

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While experts in diabetes care validate a genuine link between diabetes and vitamin D, there is no clear consensus on the effectiveness of supplements. Getty Images

A recent study published by the European Journal of Endocrinology set out to determine whether consistent vitamin D3 supplementation could improve insulin sensitivity in patients either newly diagnosed with type 2 diabetes or at high risk of developing the disease.

Consisting of 96 randomized patients, the double-blind, placebo-controlled trial included giving patients 5,000 international units (IUs) daily for 6 months.

“In individuals at high risk of diabetes or with newly diagnosed type 2 diabetes, vitamin D supplementation for 6 months significantly increased peripheral insulin sensitivity and ß-cell function, suggesting that it may slow metabolic deterioration in this population,” explained the recent report.

However, past research has failed to find a benefit from vitamin D supplementation on insulin sensitivity.

Prior to this most recent research, the largest study on vitamin D’s effect on insulin sensitivity and secretion included dosages of 4,000 IUs for nearly three years. The results were unimpressive with only a 2 percent difference between the group that did develop type 2 diabetes and the group that did not.

Was the success of this recent study the result of looser standards, or was the dosage of 5,000 IUs per day finally high enough to have a noticeable impact?

Researchers suggest past studies may have failed to prove the benefits of vitamin D supplementation due to variables including ethnicity, glucose tolerance, and vitamin D dosage and duration during the study.

Experts in diabetes care validate a genuine link between diabetes and vitamin D.

Low levels of vitamin D is a prevalent issue in people with and without diabetes across the globe. Research has repeatedly found a clear association between low vitamin D levels in patients with insulin resistance and a high risk of developing type 2 diabetes, as shown in this 2011 study from Canada.

“This newest study appears to show that with supplementation prior to diagnosis, or soon after, the body retains the ability to respond better on the cell level to insulin, which counters the hallmark of type 2 diabetes — insulin resistance,” Jennifer Smith, CDE, RD, told Healthline.

“The other thing it appears to help with is allowing the beta cells in the pancreas that make insulin to stay healthy and functional,” added Smith, who treats patients with all types of diabetes across the globe at Integrated Diabetes Services.

Beta cells play a central role in insulin secretion. Gradual beta cell dysfunction is the biggest culprit of type 2 diabetes for approximately 60 percent of people diagnosed, according to a 2016 study published in Diabetes Care.

The remaining 40 percent, then, is potentially able to reverse the condition through significant changes in nutrition, exercise, and body weight.

“Usually as type 2 diabetes progresses, patients will need to start using insulin due to gradually significant beta cell loss. This means that the oral medications for diabetes that encourage the body to produce more insulin aren’t helpful any longer — making insulin injections unavoidable.”

Despite the study’s positive findings on insulin sensitivity and production, it also reported very little difference between the placebo group and the control group concerning fasting glucose levels and HbA1c levels.

Vitamin D can positively impact insulin secretion in several ways, explained Smith, citing research from the National Institute of Health.

Vitamin D enters the beta cell and interacts with several types of receptors, which bind together and essentially activate the insulin gene, increasing the synthesis of insulin.

It’s also believed that vitamin D helps beta cells survive in a person with diabetes — whose body is otherwise trying to gradually destroy those cells — by interfering with the effects of cytokines, which are produced by the immune system.

Vitamin D also plays a critical role in regulating the body’s use of calcium. And calcium actually plays a small but critical role in the secretion of insulin. If too little vitamin D impairs the body’s ability to manage calcium levels, it inevitably impairs the body’s ability to produce insulin.

Through the same receptors associated with vitamin D’s impact on insulin secretion, vitamin D stimulates receptors that affect insulin sensitivity. Through a complicated physiological process, the interaction and binding with these receptors actually increase the number of total insulin receptors present in the body.

It’s also believed that vitamin D improves insulin sensitivity by activating other receptors that help regulate the metabolism of fatty acids within muscle and body fat.

Like vitamin D’s relationship with calcium and insulin secretion, calcium’s presence is essential for both muscle and fat’s response to insulin, enabling the uptake of insulin and glucose. Without calcium, this cannot happen. And without vitamin D, there is no calcium.

Despite the hopeful results, some diabetes experts are skeptical of this recent research’s claim that noticeable changes in insulin sensitivity and insulin production were demonstrated.

“This seems to me to be a rather fuzzy result,” Gretchen Becker, medical journalist and author of The First Year: Type 2 Diabetes, told Healthline.

“There are so many studies showing that Factor X or Factor Y or Food A or Food B improves insulin sensitivity that I’ve stopped paying attention to them,” said Becker.

Becker also points to a study reported on by Healthline warning of the dangers of consuming too much vitamin D.

“And yes, vitamin D helps your body take up calcium, but too much calcium is not good either.”

Smith agrees.

“Caution should be taken with vitamin D dosages, for people with or without diabetes,” said Smith. “The standard dosage is 400 IUs per day, but for those with diabetes, the current recommended safe daily dose to maintain optimal vitamin D levels is 1,000 to 2,000 IUs per day.”

For patients whose bloodwork reveals a vitamin D deficiency, Smith said larger doses — 4,000 daily or 50,000 IUs weekly — can be taken for short periods of time to adequately improve vitamin D levels.

“Taking high doses of vitamin D for long periods of time can lead to some troubling side effects, especially higher levels of calcium in the blood,” explained Smith.

Excessive levels of calcium in the blood, known as “hypercalcemia,” can actually weaken your bones, cause kidney stones, and interfere with the basic functions of your heart and brain.

Smith cautions that excessive vitamin D and calcium is dangerous for other health conditions — including kidney disease, which is common in people with diabetes.

“For some patients with certain health conditions — like histoplasmosis, hypoparathyroidism, lymphoma, kidney disease, sarcoidosis, tuberculosis and more — large doses of vitamin D could be a problem.”

Smith added that certain medications can interact negatively with vitamin D, so it is critical to talk to your doctor and have your levels tested properly rather than heading to the local drug store and starting your own supplementation regimen.

“Talk to your doctor, get your levels tested,” said Smith. “The appropriate approach to vitamin D supplementation can be determined from there.”

Ginger Vieira is an expert patient living with type 1 diabetes, celiac disease, and fibromyalgia. Find her and her books on Diabetes Strong, and connect with her on Twitter and YouTube.