Can Vitamin D deficiency cause Diabetes?
Diabetes mellitus (DM) is one of the major health problems affecting more than 300 million individuals in the world, with significantly higher death rates.
It is a chronic medical condition, where the blood glucose level is more than normal. In the case of type 1 diabetes, the body can’t produce enough insulin to move glucose into cell thereby increase in the blood glucose level. Whereas, in the case of type 2 diabetes, the body can’t respond to insulin, even if there is enough insulin in circulation. In the later stage of type 2 diabetes, the production of insulin reduces significantly.
Insulin is a hormone secreted by the pancreas. Insulin helps blood sugar to move from blood circulation to different cells where the glucose is being processed for energy production. There are various medicines available to keep the blood glucose level in control. However, new studies suggest a correlation between the occurrence of diabetes and blood vitamin D level. This article takes an in-depth look at Vitamin D’s effect on diabetes.
What is Vitamin D
Vitamin D is commonly known as “sunshine vitamin”. This is because Vitamin D is produced when sunlight falls on our skin. It is a fat-soluble vitamin.
The source of vitamin D for humans are sunlight, diet, and supplements.
However, exposure to sunlight is the principal source of vitamin D 
When fair skin people sunbathe in the summer, they produce almost 20,000 IU in 30 minutes. Which is almost equivalent to drinking 200 glass of milk.
However, people living at equator don’t get enough exposure to the sun to meet their requirement of Vitamin D level. At certain equators, people don’t get sun exposure for six months.
Vitamin D is essential to carry out various functions such as calcium absorption, muscle functions, immunity etc.
Vitamin D deficiency may lead to the occurrence of various diseases such as hypertension, cardiovascular disease, diabetes, immune disorders, osteoporosis and cancers 
Vitamin D deficiency can only be diagnosed by measuring the serum concentration of 25-hydroxyvitamin D (25(OH)D). The serum concentration of 25(OH)D should be measured at least twice a year. 
People with diabetes should maintain 55-70 ng/mL serum concentration of 25(OH)D.
Breastfeeding infants, older people, dark skin individuals and people who do not get exposed to sunlight are more prone to Vitamin D deficiency.
A very little is known about the metabolic clearance of vitamin D. But in the case of diabetes, vitamin D is cleared so rapidly. It might be due to 25(OH)D is used up faster to make 1,25(OH)2D to fight the disease. 
Read this article: HOW TO EAT MORE AND STILL KEEP THE BLOOD SUGAR LEVEL UNDER CONTROL
How is Vitamin D deficiency linked to the development of Diabetes?
Studies have shown a strong correlation between the deficiency of vitamin D and the occurrence of type 1 and type 2 diabetes. Vitamin receptors are abundantly found in the Beta cells of the pancreas which secrete insulin hormone and hydroxylase enzyme. 
According to a study, when Vitamin D was supplemented with South Asian women living in New Zealand who had insulin resistance, vitamin D supplement effectively reduced insulin resistance in them.
Which clearly indicate that vitamin D deficiency may be responsible for causing insulin resistance.
Vitamin D supplementation significantly increased the insulin biosynthesis in the islets of rat pancreas, as well as the increased conversion of proinsulin to insulin. 
Vitamin D deficiency can greatly reduce calcium absorption thereby causing calcium deficiency in the body. There are studies which indicate that calcium can affect insulin secretion. Which indicate that vitamin D deficiency can indirectly affect insulin secretion. 
All these studies indicate that the mechanism by which vitamin D supplement can be supportive in the management of diabetes is probably through increasing insulin release, reducing insulin resistance or indirectly affecting the secretion of insulin.
All these evidence can be further supported by several other studies. Vitamin D and calcium supplement can reduce the risk of type 2 diabetes according to a research carried out on women. 
Some observational studies were carried out to find the possible correlation between vitamin D deficiency and Type 1 diabetes. It was found that the incidence of type 1 diabetes was more in high latitude region as compared to low latitude geographical region. Which might be due to lower exposure to sunlight and vitamin D deficiency in them. 
Vitamin D supplement is highly necessary during the initial years of children to prevent future occurrence of type 1 diabetes in them. 
In another research, it was found that vitamin D supplementation in the early childhood of some children decreased the development of type 1 diabetes significantly in them as compared to the children who were not supplemented with vitamin D at early childhood. This result was found to be dose-dependent. 
Vitamin D supplement is crucial in pregnant women as well as in breastfeeding women to keep the serum level of Vitamin D to the optimal level. As we know, Vitamin D plays a vital role in the development of immunity as well as development and differentiation of the fetus, which indicate that vitamin D could play a vital role in the prevention of development of type 1 diabetes in children. 
All these findings point towards the development of diabetes probably due to deficiency of vitamin D. However there is no specific mechanism explained till date responsible for causing Diabetes due to Vitamin D deficiency. So, further investigation is needed to find out the mechanism involved in this.
Sources of Vitamin D to prevent the development of Diabetes.
Vitamin D deficiency can be prevented either by vitamin D supplementation or by exposing the skin under sunlight. You will be surprised to know that Vitamin deficiency is more common than you think. To get enough of the Vitamin D, one can expose hand, legs, face, and palm under sun twice or thrice a week till one-fourth of the time it takes for a mild sunburn to occur. Our body fat can store Vitamin D and supply the stored Vitamin to our body when we are not exposed to sunlight and need Vitamin D.
Apart from sunlight, there are various food sources of vitamin D, such as egg yolk, shrimp, milk, cereal sardines, salmon, orange juice, yoghurt etc.
Sometimes we don’t get enough vitamin D through exposure to sunlight or diet, therefore it is necessary to take a supplement to meet the daily requirement of vitamin D.
Read this article: How diabetes in pregnant women is dangerous to the baby?