Vitamin D and Diabetes Type 1 and Type 2

Does vitamin D have an impact on blood glucose?

Does supplementing vitamin D prevent the onset of diabetes type 1?

Does vitamin D supplementation improve insulin sensitivity?

How much vitamin D should a diabetic take?

Vitamin D: The Sunshine Vitamin

Vitamin D is a fat-soluble vitamin. It is essential for bone health and maintaining calcium levels in our body.

Our bodies can produce inactive forms of vitamin D from fatty tissue in the skin after exposure to sunlight. It is also called the “sunshine vitamin”.

A two-step process in the liver and the kidneys then activates the inactive form of vitamin D. 

The liver converts the inactive vitamin D to 25-hydroxy vitamin D or Calcidiol. The last step of vitamin D activation occurs in the kidneys.

Under the influence of parathyroid hormone, the kidneys convert calcidiol to 1-25-hydroxyvitamin D or Calcitriol. Calcitriol is the most active form of vitamin D.

Individuals with kidney or liver disease may not be able to activate vitamin D into its active form of calcitriol resulting in low calcium and weak bones.

It is also possible to obtain vitamin D from our food. Some of the vitamin D-rich foods include:

• Animal-based Sources of Vitamin D:

The best sources to obtain vitamin D from are fatty fish, these include salmon, mackerel, and sardines.

Fatty fishes are high in protein and have high concentrations of vitamin D which are an excellent source for individuals with deficiencies.

Other animal sources of Vitamin D are egg yolk, animal liver, and red meats such as beef, lamb, and venison. 

• Plant-based Sources of Vitamin D (Vitamin D for Vegans):

Vitamin D can also be derived from plant-based alternatives for individuals who are vegetarians, vegans, or just may not like to consume meat and animal-based products.

Plant-based alternatives include an array of milk such as almond milk, soy milk, and fortified soy milk to name a few.

Other options are spinach, carrots, mushrooms, fortified cereals, tofu, yogurt, and fortified orange juice to name a few.

These options are vegan and vegetarian-friendly and can cater to these individuals and their lifestyle choices. 

However, most people have a diet that is not sufficient to produce enough vitamin D. Thus, Vitamin D supplements are commonly used to prevent its deficiency and to improve bone health.

• Vitamin D Supplements:

Two forms of vitamin D supplements are available, Vitamin D2 and Vitamin D3. Vitamin D2 is also called Ergocalciferol which is commonly obtained from plant sources.

Vitamin D3 is Cholecalciferol. It is usually obtained from animal sources. Vitamin D3 is preferred as it is more effective than Vitamin D2.

The active form of vitamin D is 1,25 di hydroxycholecalciferol. It is also called calcitriol. It is the most active form of vitamin D and does not need activation in the body.

However, because its effects are very short-lasting, 1-hydroxy cholecalciferol or alfacalcidol is the preferred active form used where necessary.

The active forms of vitamin D are usually required by patients who have kidney disease or those who have hypoparathyroidism.

Does Vitamin D Prevent Diabetes?

Vitamin D has direct and indirect effects on blood glucose and insulin secretion.

In animal studies, it was observed that mice lacking vitamin D receptors had impaired insulin secretion.

Vitamin D receptors are present over the surface of Beta-cells of the pancreas. The stimulation of these receptors directly causes glucose-dependent insulin secretion.

Vitamin D may also preserve Beta Cells by inactivating nuclear factor–κB (NF-κB) and causes insulin secretion via regulating Calbindin, a calcium-binding protein found in pancreatic Beta cells (and many other tissues).

In a meta-analysis, Vitamin D supplementation reduced the risk of diabetes by 15%. The 3 years-absolute risk reduction was estimated as 3.3%.

Vitamin D supplementation lowered diabetes risk by 76% in those with vitamin D levels of 15 nmol/L or more compared to those with vitamin D levels between 50 – 74 nmol/L. 

In those with higher vitamin D levels, the absolute risk reduction after a 3-year follow-up was 18.1%.

Similarly, in individuals with preexisting diabetes, Vitamin D improved hyperglycemia to normal by 30%.

Side effects were not significant compared with a placebo medicine for kidney stones, hypercalcemia, hypercalciuria, or death.

Does Vitamin D Improve Insulin Resistance?

Yes. Vitamin D improves insulin sensitivity by increasing the expression of insulin receptors on target tissues.

In addition, Vitamin D activates peroxisome proliferator-activated receptor δ, enhancing insulin sensitivity and regulating fatty acid metabolism in insulin-responsive tissues.

In addition, vitamin D deficiency leads to an increase in parathyroid hormone levels via the negative feedback mechanism. High levels of parathyroid hormone in the blood can lead to insulin resistance.

Another mechanism, not studied in detail but is important to mention here is the effect of vitamin D on the RAAS system (Renin-Angiotensin-Aldosterone System).

Angiotensin II activates NF-κB which in turn causes insulin resistance in skeletal tissues via several mechanisms [Ref].

Vitamin D also exerts anti-inflammatory effects by inactivating NF-κB. Because inflammation strongly influences insulin resistance, the anti-inflammatory effects of Vitamin D improve insulin sensitivity.

Does Vitamin D Have a Role in Type 1 Diabetes?

Vitamin D supplementation has been shown to improve dysglycemia, and insulin resistance, and preserve Beta-cell function in type 2 diabetic individuals.

However, does vitamin D have any role in improving glucose control or preventing Type 1 Diabetes?

Several studies show a positive link between Vitamin D supplementation early in childhood and the incidence of Type 1 Diabetes [Ref].

Vitamin D supplementation may also delay the depletion of Beta cells as measured by absolute or near-absolute C-peptide deficiency. However, once Type 1 diabetes develops, it has little role in disease regression [Ref].

Still, vitamin D supplementation may mitigate asthenia and fatigue associated with diabetes and improve glucose control.

How Much Vitamin D Should a Diabetic Take Daily?

The usual recommended dose of vitamin D is 400 IU to 800 IU per day.

For treatment purposes and for improving insulin resistance, preserving Beta cell functions, and preventing diabetes, studies indicate a higher-than-usual dose [Ref].

It is safe to take up to 2000 IU of Vitamin D daily if a person is deficient or has low normal vitamin D levels.

Higher doses may also be indicated in diabetic patients with associated skeletal problems like osteopenia, and osteoporosis, and those on concomitant bone-resorbing medications such as corticosteroids.

Combining Vitamin D3 and K2 may enhance the effects of Vitamin D3. However, the role of combining Vitamin D3 and K2 in preventing diabetes or improving insulin resistance has not been adequately studied.

In Conclusion:

There are studies supporting the role of supplementing vitamin D in patients with Type 1 Diabetes Mellitus as well as Type 2 Diabetes Mellitus.

However, it is important to not miss your diabetes medications or delay treatment initiation hoping vitamin D will cure your diabetes.

Take vitamin D supplements if you are deficient or have symptoms and signs of vitamin D deficiency along with your diabetes medications.