There is a link between vitamin D deficiency and insulin resistance, diabetes, and overweight

A growing number of people suffer from overweight and type 2 diabetes, both of which are problems that come at a cost both to society and to the individual. The traditional dietary guidelines are not of much use, and many people find themselves in a hopeless battle because they also suffer from insulin resistance with impaired cellular glucose uptake. Countless epidemiological studies have demonstrated that the widespread lack of vitamin D contributes to the problem. In a review article that is published in Nutrients, the scientists address vitamin D’s many functions with relation to blood glucose regulation, satiety, body weight, and prevention of type 2 diabetes. It should be noted that overweight people and type 2 diabetics may have an increased need for vitamin D, and magnesium is also required for activating the vitamin.

Overweight, obesity and type 2 diabetes are closely related. These problems are preceded by insulin resistance, which typically goes unnoticed. Insulin resistance is when the cellular uptake of glucose gradually decreases. Consequently, people don’t feel properly satiated and tend to develop cravings for fast carbohydrates, which are known to make blood sugar levels oscillate. At the same time, excess calories are removed from the bloodstream and stored as potentially harmful fat. The early stage of type 2 diabetes is called metabolic syndrome and is characterized by insulin resistance, elevated cholesterol levels, and excess body fat, primarily in the form of visceral fat around the intestines. Both metabolic syndrome and type 2 diabetes are characterized by low-grade inflammation that is extremely harmful and sets the stage for oxidative stress and cardiovascular disease. It is therefore not cholesterol in our diets that causes the problem, it is derailed sugar metabolism.
There is an established relation between vitamin D deficiency, overweight, and type 2 diabetes, an in their review article, the authors look closer at how vitamin D regulates insulin sensitivity, genes, and inflammatory processes in overweight individuals.

Vitamin D deficiency and obesity

Obesity is a pathological condition that is characterized by excess body weight and too much fat as a result of food dependence, genetic mutations, a sedentary lifestyle, endocrine disorders, and poor nutritional status. It is commonly known that obesity is associated with morbid conditions like metabolic syndrome, diabetes, hypertension, pulmonary ailments, non-alcoholic fatty liver disease (NAFLD), bone alterations, and cancer. Moreover, obesity is linked to low blood levels of vitamin B1, folic acid (vitamin B9), and vitamin D.
For the past thirty years, several epidemiological studies have shown that our modern lifestyle combined with widespread vitamin D deficiency contribute to the detrimental rise in obesity and the serious complications that follow in the wake of it, typically metabolic syndrome, type 2 diabetes, and cancer.
Studies also show that obesity, metabolic syndrome, and diabetes as single factors increase the risk of vitamin D deficiency. This is primarily a result of many overweight people being physically inactive and not getting out in the sun enough. But it is also a result of unhealthy eating habits. And finally, obese people have difficulty with converting vitamin D from sunlight and food sources into its active form because of impaired liver and kidney function.
The majority of cells have vitamin D receptors (VDR). VDR and vitamin D are believed to control around 10 percent of our genes and that is relevant for glucose tolerance, insulin sensitivity, immune response, cell division, fat tissue, and bones.
In a study that was carried out three decades ago, it was shown that vitamin D in the form of 25-hydroxyvitamin D3 can block the development of fat tissue, and that triglyceride accumulation was reduced by 50% by means of different mechanisms.
VDRs are also involved in the body’s heat production (thermogenesis), which is carried out by the mitochondria in our brown fat cells. More specifically, vitamin D receptors control certain transport proteins called UCP1 and UCP2 that carry glucose into the cells via the cell membrane.
Because vitamin D is a lipid-soluble vitamin, it is primarily stored in the liver and in fatty tissue. However, even though overweight and obese individuals have far more tissue than others, it appears that vitamin D and its metabolites are not readily available for various vitamin D-dependent body functions. Therefore, overweight and obese people may need more vitamin D.

Vitamin D deficiency, insulin resistance, and diabetes

Insulin resistance is the leading cause of type 2 diabetes. The condition is insidious and takes years to develop. It is often a result of consuming far too much carbohydrate – especially the refined ones – and lacking vitamin D.
When we ingest carbohydrates, they are broken down into glucose. The pancreas then produces insulin, the hormone that helps glucose enter our cells. When people have insulin resistance, they produce low-quality insulin that results in permanently elevated blood glucose levels. Consequently, the cells do not get enough glucose, which is their primary source of fuel.
Vitamin D has the following functions:

• The insulin-producing beta cells of the pancreas have vitamin D receptors (VDR). It is believed that vitamin D is required for the conversion from pro-insulin (a precursor of insulin) into insulin
• VDR and vitamin D play a role in the pancreatic insulin production and insulin release
• VDR and vitamin D enhance insulin sensitivity and blood glucose uptake in the liver, muscles, brain, and other tissues
• Vitamin D regulates the transport protein GLUT-5 in muscle cells. The protein is important for cellular glucose uptake
• Vitamin D receptors (VDR) have been found in the hypothalamus, which is major center in the brain. Science already known that the hypothalamus helps control our appetite and metabolism
• Vitamin D regulates the white blood cells and pro-inflammatory cytokines of the immune defense. In other words, vitamin D helps control low-grade inflammation that is typically seen with obesity, insulin resistance, and type 2 diabetes. This type of chronic inflammation that goes unnoticed generates large quantities of free radicals, which cause oxidative stress and attack cholesterol, setting the stage for atherosclerosis.

Vitamin D deficiency, supplementation, and insulin resistance

As mentioned earlier, numerous studies have already documented an inverse relation between blood levels of vitamin D and the development of obesity, insulin resistance, metabolic syndrome, and type 2 diabetes in both children and adults.
Many studies have even showed that vitamin D supplements can improve insulin sensitivity and glucose tolerance. Nonetheless, there have been different results in terms of the effect of vitamin D supplementation on overweight people and diabetics. This is because scientists have looked at different populations and used different vitamin D doses with or without calcium. Also, the vitamin D supplements that were used in different studies were not all the same quality. Vitamin D has the best bioavailability when it is bound to oil in capsules.
One should also take into account the fact that insulin resistance, obesity, and type 2 diabetes increase the need for vitamin D, and the big question then is what dosage is optimal for each individual. With regard to vitamin D’s impact on insulin sensitivity and diabetes, other nutrients also play a significant role.

Vitamin D supplementation and optimal levels

At our latitude, the sun sits too low in the sky during the winter period for us humans to synthesize vitamin D in our skin. Many scientists propose taking 50-80 micrograms of supplementary vitamin D during the winter period to optimize blood levels of the nutrient. All-year supplementation may be necessary in situations where there is also too little sunlight during the summer period.
Vitamin D in the blood is measured as 25-hydroxyvitamin D3. The official threshold value is 50 ng/ml, but according to leading scientists, this is too little, and they recommend up to 75-100 ng/ml for optimal disease prevention.

Magnesium is required to activate vitamin D

A magnesium deficiency may result in poor utilization of vitamin D, which is because we need magnesium-containing enzymes to helps with the conversion of vitamin D from sunlight or supplements into the active forms. This conversion takes place in the kidneys and liver.
A study that is published in the American Journal of Clinical Nutrition shows that magnesium helps regulate and optimize blood levels of vitamin D.

Did you know that the trace element chromium also plays a role in insulin sensitivity?

References

Emanuela A. Greco et al. Role of Hypovitaminosis D in the Pathogenesis of Obesity-Induces Insulin Resistance. Nutrients 2019

Scott LaFee. Vitamin D Deficiency Linked to Greater Risk of Diabetes. UC San Diego Health. April 2018

Plasma 25-hydroxyvitamin concentration and risk of type 2 diabetes and pre-diabetes. 12-year cohort study. PLoS One 2018

Iowa State University: New promise for diabetics with vitamin D-deficiency. ScienceDaily. 2016

http://slankeviden.dk/nyheder/diabetes/51-mangel-pa-d-vitamin-i-hjernen-oger-fedmerisiko.html

Gerry K. Schwalfenberg and Stephen J. Genuis. The Importance of Magnesium in Clinical Healthcare. Scientifica (Carro) 2017

Qi Dai et al. Magnesium status and supplementation influence vitamin D status and metabolism; results from a randomized trial. The American Journal of Clinical Nutrition 2018

Pernille Lund. Sådan får du styr på dit blodsukker. Ny Videnskab 2013