Vitamin D Can Prevent and Treat Diabetes
More than 460 million people, almost 6% of the world's population, are suffering from type 2 diabetes, the most common form. Over 1 million deaths per year can be attributed to this condition, which makes it a leading cause of death. And the number of new cases is constantly increasing worldwide. By 2030, more than 7% will be suffering from type 2 diabetes. 
Besides the high number of fatalities caused by diabetes in "normal", non-pandemic years, it is also one of the most important risk factors for severe or fatal courses of Covid-19. A new meta-analysis shows that diabetes is responsible for 17% of deaths from Covid-19. Diabetes is a strong risk factor for fatal courses of infectious diseases. To date, there are more than 7.5 million official Covid-deaths. Based on the results of the new meta-analysis, approx. 1.3 million of these deaths could have been avoided if no one in the world suffered from diabetes. 
Diabetes has various causes and risk factors, including an unhealthy pro-inflammatory diet, lack of physical activity, overweight/obesity, several micronutrient deficiencies, and mitochondrial dysfunction.  Diabetes can be greatly reduced and even reversed using a low-carbohydrate diet, a ketogenic diet, or intermittent fasting. [4-6] However, this article will focus on the role of vitamin D.
Type 2 diabetes
Recent evidence shows that a sufficient supply of vitamin D can protect from the most common forms of diabetes: type 2, type 1 and gestational diabetes. Meta-analyses of observational studies have shown that a low vitamin D level is an independent risk factor for the development of type 2 diabetes.  Individuals with a vitamin D level >25 ng/ml had a 43% lower risk of developing type 2 diabetes than those with a severely deficient level below 14 ng/ml.  Similarly, another study with people who had normal glucose levels or prediabetes showed that those with a level above 28 ng/ml had a 42% lower odds of developing or progressing to type 2 diabetes compared to those with a level below 18 ng/ml. 
However, the optimal range is well above 30 ng/ml. In a trial with women who were suffering from insulin resistance (which is the preliminary stage of type 2 diabetes) and had a deficiency of vitamin D, daily supplementation of 4000 IU for several months improved insulin resistance and insulin sensitivity more than a placebo. Importantly, insulin resistance was most strongly improved at or above 32 ng/ml. They found that the optimal level for the reduction of insulin resistance and thus for the prevention of type 2 diabetes was between 32 and 48 ng/ml.  In line with this finding, a study conducted by the health organization Grassrootshealth showed that a level of 41 ng/ml is associated with a 60% lower risk of developing type 2 diabetes compared with a level of 22 ng/ml. 
Several recent meta-analyses of RCTs (randomized controlled trials) showed that the association between a higher vitamin D level and a lower risk of type 2 diabetes is causal and dose-dependent. In patients with prediabetes, supplementation of vitamin D significantly reduced the risk of progressing to type 2 diabetes. [12,13] Supplementation to a higher vitamin D level (≥ 50 ng/ml vs. ≤ 30 ng/ml) reduced the risk for diabetes by a larger amount (76%).  The higher the level achieved, the more beneficial effect, up to ~60 ng/ml. This effect was more strongly pronounced in non-obese patients.
Since people with more weight or body fat need more vitamin D to reach a healthy level, it is likely that obese people did not receive the amount of vitamin D they required and therefore did not experience the same strong risk reduction as the non-obese people. Patients with prediabetes who received vitamin D also had a ~50% greater chance of reversing to a normal pre-diabetic state. The optimal vitamin D dose depends on many factors including the body weight and magnesium status. Vitamin D levels higher than 150 ng/ml can contribute to toxicity but are rare.
Direct mid-day summer sunlight on the skin can make adequate vitamin D with enough skin exposure. However sunlight does not cause vitamin D toxicity because at high vitamin D levels the body stops making it. Exposure to sunlight when the sun is less than 45 degrees above the horizon, or to sunlight through a glass window, though it can cause tanning, does not produce vitamin D (UVB light is required). Most of us don't get enough vitamin D from our limited exposure to sunlight, especially in the winter. And although dermatologists warn that sun exposure can cause skin cancer, recent evidence suggests that moderate sun exposure (that produces vitamin D) may be protective against cancer.
Since 75% of the global adult population has an insufficient vitamin D level ( < 30 ng/ml ),  most are at increased risk of developing diabetes. Therefore it is not surprising that diabetes is on the rise worldwide. The vitamin D insufficiency situation is severely disease-promoting.
On the other hand, if all people had a very sunny level of vitamin D (40-60 ng/ml) probably most cases of type 2 diabetes could be prevented, which would also help to prevent many of the yearly 1 million deaths from diabetes. Further, as described above, more than a million deaths from Covid-19 are attributable to diabetes. Thus, a widespread correction of the worldwide vitamin D deficiency would have resulted in fewer deaths from infectious diseases like Covid-19.
Many doctors and researchers tried years ago to inform the public and governments about the "vitamin D deficiency pandemic". [16-18] Unfortunately, there was hardly any interest in solving this tragedy. The reason is clearly described in an article by William Grant.  If your doctor tells you that a vitamin D level between 20 and 30 ng/ml is a "sufficient level", refer to that article and explain that such levels are severely insufficient and strongly increase the risk of developing disease conditions such as infections and diabetes.
Besides lowering the risk of developing type 2 diabetes, vitamin D also helps to reverse the disease. In patients with type 2 diabetes and low vitamin D levels, supplementation with vitamin D significantly lowered blood glucose levels (fasting glucose level and long-term blood glucose value HbA1c) and improved insulin resistance. 
Type 2 diabetes is reversible with anti-diabetes drugs along with a protocol consisting of a temporal, slight caloric restriction, change to a healthy plant based diet, exercise and weight loss. After 12 months on such a protocol, approx. 50% of patients with type 2 diabetes achieved remission to a non-diabetic state and no longer required antidiabetic drugs.  Had the diabetic patients received ideal amounts of vitamin D as an addition to this program, the remission rate after 1 year would likely have been much higher.
Vitamin D also helps prevent and treat several of the complications that may arise from diabetes. For example, diabetics have twice the risk of developing depression compared with non-diabetics , and recent RCTs have shown that vitamin D effectively reduces depressive symptoms and may help prevent the development of major depressive disorder in patients with type 2 diabetes. [23,24] Diabetics also have increased cancer risks  and vitamin D has anti-cancer effects, with meta-analyses of RCTs showing that supplementation of vitamin D significantly reduces cancer mortality. 
About half of diabetics develop peripheral neuropathy, which is a form of nerve damage (due to increased glucose and decreased circulation) that affects limbs like legs, feet and arms and causes very uncomfortable and painful symptoms.  A deficiency of vitamin D seems to increase the risk of peripheral neuropathy. Supplementation with vitamin D in patients with diabetic peripheral neuropathy resulted in significantly reduced pain scores (up to 50% lower pain score after several months of continuous intake). 
Diabetic foot ulcers (a combination of neuropathy and ischemia) are one of the most devastating consequences of diabetes. Every year, millions of diabetics develop foot ulcers and up to 33% of all diabetics worldwide will suffer from a foot ulcer during their lifetime. Such ulcers often require amputation of lower limbs. Also, diabetics who develop foot ulcers have a 5-year mortality rate 2.5 times higher than those who did not develop such ulcers. 
A low vitamin D level is associated with a strongly increased risk of developing diabetic foot ulcers, suggesting that a sufficient level would reduce the incidence of this complication.  Also, vitamin D supplementation significantly hastened the healing process of diabetic foot ulcers.  Recent studies have confirmed that along with vitamin D, a sufficient supply of both magnesium and zinc is equally important to cure such ulcers. [32,33]
Cofactors of vitamin D also have an important role in the prevention of type 2 diabetes. Deficiencies of magnesium and vitamin K2 are very common among the public with almost half of the US population having an inadequate intake of magnesium  and up to 97% of older people suffering from an insufficiency of vitamin K2.  Type 2 diabetes is associated with low magnesium levels,  and a high dietary intake of magnesium was associated with a lower risk of developing type 2 diabetes.  Also, magnesium supplementation helps treat prediabetes and type 2 diabetes, and significantly reduced glucose parameters and improved insulin sensitivity in such patients.  Type 2 diabetics have significantly lower vitamin K2 levels than healthy controls,  and supplementation of K2 significantly reduced glucose levels (fasting glucose and HbA1c) in patients with diabetes. 
The incidence of type 2 diabetes would likely be drastically reduced if all people could get adequate amounts vitamin D and its most important cofactors like magnesium and vitamin K2.
Type 1 diabetes
Type 1 diabetes is an autoimmune disease, and recent evidence from the VITAL study shows that long term supplementation with vitamin D significantly reduces the risk of developing autoimmune diseases. [40,41] Regarding the specific diagnosis of type 1 diabetes, a sufficient level of vitamin D compared to the lowest levels reduces the risk of type 1 diabetes by approximately 60%. A level of ~45 ng/ml was associated with the lowest risk (72% lower) of type 1 diabetes.  A sunny level above 40 ng/ml seems to optimize protection against autoimmune conditions. Note again that world-wide, most adults have an insufficient level below 30 ng/ml -- and it appears that most are unaware of this important information.
Other meta-analyses showed that supplementation of vitamin D during infancy is associated with ~30% lower risk of developing type 1 diabetes later in life, [43,44] suggesting that vitamin D helps the immune system to develop better.
The risk of developing type 1 diabetes can be reduced with a sufficient level of vitamin D. But even if the disease is already established, vitamin D should be considered as a treatment. RCTs show that vitamin D supplementation may attenuate the "natural history of the disease", by improving fasting and stimulated C-peptide levels, allowing a lower required insulin dose. This indicates that the performance of the pancreas has improved due to vitamin D. 
Importantly, since type 1 diabetes is an autoimmune disease, it may be strongly improved or (depending on the stage) even brought into remission by the coimbra-protocol. The coimbra-protocol has shown to be a remarkably effective treatment for many forms of autoimmune conditions. Its central component is very high dose vitamin D. People who are interested in the coimbra-protocol should work together with a therapist or doctor who is trained in the protocol. Search for coimbra-doctors. The daily doses are much higher than what is typically recommended by vitamin D researchers and may lead to negative effects if they are not constantly adjusted based on several lab parameters. In order to make the treatment work and to prevent harm from high levels of vitamin D, the dose needs to be adjusted based on individual needs and testing results, the diet needs to be adapted (low calcium, etc.), and frequent blood examinations are required to make sure that no safety issues occur. However, contrary to some of the typical negative anti-vitamin D articles in the mainstream press, the experience of many coimbra-therapists around the world with thousands of strongly improved patients and published data of many individuals shows that the coimbra protocol is reliably safe if the patients are adequately supervised by trained coimbra-therapists/ physicians.  Those who use this protocol for the treatment of an autoimmune disease are likely to experience strong clinical improvements or even remission.
Gestational diabetes mellitus
In line with other forms of diabetes, the incidence of gestational diabetes mellitus (GDM) is increasing and affects millions of pregnant women worldwide. In the USA, up to 10% of pregnant women develop the condition.  It is one of the most common complications during pregnancy, and increases the risk of adverse pregnancy and neonatal outcomes like preterm delivery, cesarean delivery, or respiratory distress syndrome in the infant or requiring admission to the neonatal ICU.  Also, women who develop gestational diabetes (GDM) have a high risk of developing type 2 diabetes in the following years.
A deficiency of vitamin D seems to be an important cause. Women with a low level of 25(OH)D had a significantly higher risk of GDM than those with a sufficient level.  A meta-analysis of RCTs proved that supplementation of vitamin D during pregnancy improves blood glucose levels and reduces the risk of developing gestational diabetes by 58%.  Of note, a daily dose of > 2000 IU is required for the prevention of diabetes during pregnancy.  Many cases of GDM may be preventable with a sufficient supply of vitamin D.
In addition, vitamin D supplementation in pregnant women with GDM can massively reduce the risk of adverse neonatal outcomes. In fact, in women with GDM, supplementation of vitamin D decreased the risk of premature delivery by 63%. Similarly, the risk of the neonates requiring hospitalization after birth was reduced by 62% due to vitamin D supplementation during pregnancy.  This means vitamin D not only prevents GDM, but in women who have developed the condition it can also protect the unborn from harm caused by the disease and decrease the risk of negative fetal and neonatal health outcomes.
And importantly - independent from gestational diabetes- supplementation of sufficient amounts of vitamin D during pregnancy can also save many lives. A new meta-analysis of RCTs has shown that vitamin D supplementation in adequate doses during pregnancy reduced the risk of intrauterine or neonatal death by more than 30%,  which may allow thousands of unborn or neonates to survive if pregnant women achieved and maintained sufficient tissue levels of vitamin D.
The level of vitamin D and its cofactors magnesium and vitamin K2 are widely deficient in individuals throughout the world. These deficiencies attenuate the function of the body's immune system and contribute to widespread disease and death that could be prevented with adequate supplements. In many cases, type 2 diabetes can be prevented and reversed with a protocol of essential nutrients that includes vitamin D, magnesium, vitamin K2, and mild dietary restriction in a low-sugar diet with colorful raw and cooked vegetables. Many people including medical professionals are unaware of the problem and its solution. Please spread the word!
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