Vitamin D’s Invisible Hand on Insulin Resistance

The consequences of vitamin D deficiency extend beyond just bone health. It has many implications in causing insulin resistance, increasing Body Mass Index (BMI) and raising blood pressure.

For many years, obesity has been the top culprit for Type II Diabetes. As a result, most overweight individuals are thought to be pre-diabetic. Physicians have blamed Type II Diabetes primarily on over-eating, lack of exercise and over-consumption of sugars. However, although the nutrition piece of diabetes is undeniable, obesity may not be the most important factor driving the on-set of this chronic disease.

Vitamin D is an important regulator of bone health because it is heavily involved in calcium absorption in the gut and reabsorption by the kidneys. When vitamin D levels are low, the parathyroid gland secretes more Parathyroid Hormone (PTH). PTH stimulates the conversion of vitamin D to the active form, induces the bone to release free calcium into the blood and up-regulates the reabsorption of calcium in the kidneys.

Vitamin D deficiency results when serum levels fall under 15 ng/mL because below this threshold, PTH levels significantly increase. The condition during which the body produces excess PTH is called hyperparathyroidism. Although the body is doing the protective thing by producing more PTH to increase intracellular calcium levels when vitamin D is low, vitamin D deficiency may not necessarily be accompanied by low calcium in the body.

Since calcium is an important second messenger involved in many signaling pathways, elevated free intracellular calcium levels can go on to activate Pyruvate Kinase C activity, which is an enzyme involved in desensitizing insulin receptors, the first step to insulin resistance. Insulin resistance is a critical warning sign because the body will not be able to produce energy from food as efficiently, ultimately manifesting in uncontrolled weight gain. Furthermore, the build-up of calcium in the arteries constricts the blood vessels, thereby increasing blood pressure and the likelihood of cardiovascular episodes.

We can obtain vitamin D from dietary sources and from the sun, but the level of active form of vitamin D in the body depends on the integrity of the gastrointestinal system and the availability of vitamin D precursors. Increasing research shows that vitamin D deficiency increases overall mortality due to higher risk for insulin resistance, increasing BMI and elevated blood pressure. Due to the extensive role of vitamin D in many diseases, especially diabetes, vitamin D levels should be closely monitored and drastic supplementation measures should be taken to increase the overall quality of life.