Vitamin D and diabetes: Does deficiency of calciferol affect blood glucose level?

Vitamin D is an essential vitamin and often we associate lower levels of the vitamin with weak bone and poor muscle health. However, what we overlook is the association of this important vitamin with major diseases like diabetes.

Exposure to sunlight helps the body to synthesize vitamin D, otherwise known as calciferol, and this is considered to be one of the most effective ways to supply the body with vitamin D.

There are several research studies done on the link between vitamin D and diabetes.

Vitamin D improves the sensitivity of insulin which is of prime importance in maintaining blood glucose levels. It is related to insulin secretion, insulin resistance, and β-cell dysfunction in the pancreas. In diabetic animal models, it has been seen that the secretion of pancreatic insulin is inhibited by vitamin D deficiency.

Studies have said that in order to keep a normal glucose level a human body needs to have 80 nmol/l or above vitamin D.

Research studies on older individuals have found that blood vitamin D levels of less than 50 nmol/l doubles the risk of diabetes.

As per a report published in Diabetes Spectrum, "There is growing evidence that vitamin D deficiency could be a contributing factor in the development of both type 1 and type 2 diabetes. First, the β-cell in the pancreas that secretes insulin has been shown to contain vitamin D receptors."

"Vitamin D contributes to normalization of extracellular calcium, ensuring normal calcium flux through cell membranes; therefore, low vitamin D may diminish calcium's ability to affect insulin secretion. Other potential mechanisms associated with vitamin D and diabetes include improving insulin action by stimulating expression of the insulin receptor, enhancing insulin responsiveness for glucose transport, having an indirect effect on insulin action potentially via a calcium effect on insulin secretion, and improving systemic inflammation by a direct effect on cytokines," it adds.

Though several studies have worked on it, the outcome has mostly been poorly understood.

In a study held in Japan with 1256 adults with prediabetes to an active form of vitamin D analogue (eldecalcitol) or placebo, the risk of diabetes was also lower in the vitamin D group than in the placebo group, but the difference was again not significant.

"Vitamin D may play a role in type 2 diabetes; however, to better define the role of vitamin D in the development and progression of type 2 diabetes, high-quality observational studies and RCTs that measure blood 25-hydroxyvitamin D concentration and clinically relevant glycemic outcomes are needed," a review article published in the Nature says.

A 2021 study published in Frontiers in Endocrinology found that the recommended doses of vitamin D significantly decreased the level of HbA1c after 3 as well as after 6 months of vitamin D supplementation in patients with type 2 diabetes treated with metformin and added that it is possible that vitamin D has beneficial effects only in vitamin D deficient patients especially in those with poor glycaemic control.

Along with diabetes, vitamin D is also linked to cardiovascular health. While several studies could not establish a consistent link between vitamin D deficiency and heart health, several other studies have found that the deficiency of this essential vitamin increases the blood pressure and hence the odds of cardiovascular diseases.

However, there is no concrete conclusion on whether vitamin D supplements are the solutions to a healthy heart.

There is a strong association between diabetes and heart health. High blood sugar can damage the blood vessels and the nerves can help in the proper functioning of the heart.

High blood pressure increases the flow of blood through the arteries and puts extra pressure on the heart.

There are several factors that put the heart at tremendous risk like: smoking, obesity, less physical activity, having a diet rich in saturated fat, trans fat, cholesterol, sodium and drinking too much alcohol.

"The upper tolerable limit is 4,000 international units (IU) daily, and the recommended amount for women 14 to 70 is 600 IU per day. Women 71 and older should aim for 800 IU per day," experts at John Hopkins say.

However, an increase in the amount of vitamin D intake can lead to vitamin D toxicity.

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