Is Vitamin D Deficiency Linked With Diabetes?

Vitamin D has received more focus in public health over recent years, and with good reason when you consider ongoing advances in scientific evidence.

Research continues to emerge of an association of deficiency of vitamin D with various diseases, including respiratory diseases (although Lee et al. found no association between vitamin D deficiency and Covid19); depression, forms of dementia including Alzheimer’s disease, and diabetes mellitus.

Of course, there is also a strong link between vitamin D and osteoporosis, long known.  

This article will explore the link between vitamin D and diabetes and give an overview of vitamin D, including supplementation, vitamin D insufficiency, and foods that are good sources of vitamin D.  

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Vitamin D Supplementation

Vitamin D supplementation is recommended for many parts of the population. A test called the 25 hydroxyvitamin D test is the best way to assess vitamin D levels.

A doctor will recommend a supplement if a 25 hydroxyvitamin D test reveals a vitamin D insufficiency. A typical dose is 10ug (10 micrograms), or 400IU per day, although this will vary depending on the individual circumstances. 

Vitamin D Deficiency 

Vitamin D is not one singular vitamin. And in fact, it is not officially a vitamin at all. Exposing your skin to the sun produces Vitamin D.

Strictly speaking, vitamin D is a steroid hormone made from cholesterol following sunlight exposure.

As mentioned, vitamin D is a group of vitamins, and in this section of the article, we will discuss a few of them. 

Vitamin D2 and vitamin D3, ergocalciferol, and cholecalciferol, found in plants and animal tissues, respectively, are pharmacologically inactive.

Through hydroxylation in the liver followed by in the kidneys, we convert them to active compounds. The liver converts vitamin D3 to 25-hydroxycholecalciferol. The kidneys then convert 25-hydroxycholecalciferol to either 24,25-dihydroxycholecalciferol or 1α,25-dihydroxycholecalciferol, which is active vitamin D. 

Vitamin D has several functions, and many tissues have a vitamin D receptor. It is vital for bone metabolism, and it plays a role in ensuring optimum calcium concentrations in the blood. Vitamin D increases the absorption of calcium from the gut and reduces the amount lost by the kidneys.

Vitamin D also promotes the absorption of phosphorous from your gut. Additionally to the role vitamin D plays in bone health, it is also necessary for the good health of your teeth, muscles, and gut.

Conditions Vitamin D deficiency can commonly lead to

  • Rickets (in children)

  • Osteomalacia (in adults).

Osteomalacia is a painful bone condition that we characterize by softened bones and muscle weakness. In children, it can lead to bowing of the legs (due to rickets), which occurs due to vitamin D deficiency when children are growing. In both children and adults, it can be very painful and we treat it with vitamin D supplementation. 

The primary production of Vitamin D is skin exposure to sunlight. For this reason, we commonly call it the ‘sunshine vitamin.’

People who do not get enough sunlight for various reasons are at a higher risk of vitamin D deficiency. Particularly during the Coronavirus pandemic, most people have been spending far more time indoors, and that in itself is a risk factor for vitamin D deficiency, particularly during winter months.

People at higher risk of vitamin D deficiency

  • People who stay indoors for all or most of the time, e.g., those living in institutional care or who are housebound

  • Older adults

  • People who cover up all or most of their skin, e.g., for cultural reasons 

  • Those with darker skin tones

Vitamin D Recommendations

The recommendation for vitamin D supplementation in the UK is 10ug (10 micrograms), to be taken throughout the year. Yet, it is essential to note that some people will require higher levels of vitamin D supplementation, and individual medical advice should always be sought.

It is still recommended that you supplement those who are not at high risk during autumn and winter months if you live in a country where sunlight levels are low outside of the summer (like the UK).

During the spring and summer months, at least 15-20 minutes of sunlight exposure to your skin is recommended. Ensure you do not stay in the hot sun for long periods, and wear a suitable sun protection cream for prolonged periods in the sun.

As introduced earlier in this article, associations exist between vitamin D deficiency and diabetes. In the following section of this article, we will explore this in more detail. 

Effects on Diabetes

Studies indicate that people with low vitamin D levels have a far significant risk of chronic conditions, including diabetes mellitus (herein referred to as diabetes).

The clear link between diabetes and vitamin D is referenced in the literature, although it is not fully understood why there is a link.

Various hypotheses have been presented on the connection between prediabetes, diabetes, and vitamin D, including:

  • A link between insulin resistance and vitamin D

  • Ties between the adverse effects of inflammation and diabetes risk, concerning a low vitamin D level

  • A link between vitamin D and the defunctioning of bodily processes can lead to chronic diseases, including diabetes. 

Vitamin D Effects On Insulin Sensitivity

To expand on the above points, we know that vitamin D can help your insulin sensitivity. Insulin is a hormone responsible for regulating blood sugar levels (also called your glucose level).

Diabetes risk and diagnosed diabetes are both characterized by the onset of insulin resistance and damage or destruction of the pancreatic beta cells responsible for insulin secretion. There is also some scientific opinion that vitamin D may help regulate insulin production in the pancreas.

Despite some research showing a link between optimum vitamin D levels and improved insulin sensitivity, not all studies support this finding. One randomized control trial found an oral vitamin D supplement did not affect insulin sensitivity in people with prediabetes in 12 weeks of treatment. 

While the advice is mixed on the recommendation to start vitamin D supplementation if you are at risk of diabetes, a sensible first step would be to get your vitamin D status tested with a 25 hydroxyvitamin D test and then act on the results according to medical advice.

It is likely that if you have a low vitamin D level, your doctor will recommend you take a vitamin D supplement. You can also increase your vitamin D by eating foods containing vitamin D, although only very few foods meet this definition. 

What Foods Are High in Vitamin D Yet Also Diabetes-Friendly?

We know that sunlight exposure is the best way to improve your vitamin D status. Yet, some foods are either naturally a good source of vitamin D or are fortified with vitamin D. The following foods are a good source of vitamin D:

  • Oily fish – such as salmon, sardines, herring, and mackerel

  • Red meat

  • Liver

  • Egg yolks

  • Fortified foods – such as some fat spreads and breakfast cereals (check the nutrition panel or ingredients, where any added vitamin D is listed)

  • Milk can sometimes be fortified with vitamin D (although naturally, it is a poor source)

Of importance to many people with any form of diabetes, including type 1 diabetes, type 2 diabetes, and gestational diabetes, is the types of food they eat.

Thankfully, the above-listed foods are all good foods to include in your diet if you have diabetes. Oily fish provide several health benefits, including being a good protein source and a source of heart-healthy omega-3 fatty acids.

Red meat and liver offer a good source of iron. And egg yolks are rich in protein, vitamins B12, B2, and A. They are also a good source of folate. When choosing spreads and cereals, it is best to go for unsaturated fat spreads and wholegrain cereal products. 

As mentioned, if you have low vitamin D levels, a supplement will be the primary form of treatment.

How Much Vitamin D Should People With or at Risk for Diabetes Take?

Referring back to the evidence, recommendations are commonly made for those at risk for diabetes to supplement with vitamin D.

In individuals at high risk of diabetes or those with newly diagnosed type 2 diabetes, supplementation for six months has significantly increased peripheral insulin sensitivity and beta-cell function. In this particular study, the dose of vitamin D taken was 5000IU per day. This is a high dose that you should only take with medical supervision.

The general recommendation for daily supplementation of vitamin D is 400IU, equivalent to 10ug (10 micrograms). It is best to speak with your doctor about a suitable dose of vitamin D. They will advise you based on your clinical history and your serum vitamin D levels.

Other health benefits of Vitamin D

As mentioned in the introduction to this article, research exists and continues to emerge to the beneficial effect of having a good vitamin D status. Below is a list of conditions that link with vitamin D. 

Cardiovascular disease

The active vitamin D form, 1α,25-dihydroxy vitamin D, is again important here. It binds to the vitamin D receptor that regulates the various genes involved in essential processes linked to cardiovascular disease. In one 2014 review, low vitamin D levels relate to heart disease and associated problems, including atherosclerosis, high blood pressure, and stroke. The review also draws a link between diabetes and low vitamin D levels. Contact your doctor if you are concerned about heart disease or cardiovascular disease risk. They will assess your history and possibly recommend medication and/or diet and lifestyle modifications. 

Certain cancers

Vitamin D deficiency can link with a higher breast cancer risk and a higher prostate cancer risk. 


Research points toward a link between certain types of dementia, including Alzheimer’s disease, and moderate to severe vitamin D deficiency. This level of deficiency among older adults was associated in a study with a doubled risk for developing certain dementias. 

Depression and other mental health conditions

We will all be familiar with a sunny day, improving our mood. It may even be that you struggle with seasonal affective disorder (SAD). SAD is a condition that some people get during the long winter months. One 2017 study found that vitamin D supplementation helped improve women’s mood with type 2 diabetes. The women in this small study took a high weekly dose of vitamin D (50,000 IU) for six months. Among the findings was that the women in the study experienced a significant decrease in depression and anxiety. They also recorded a general overall improvement in mental health.


Vitamin D is a steroid hormone with many functions and receptors in the body.

Historically and in the present, it has generated lots of interest toward its link with other diseases. An optimal vitamin D status links to a reduced risk of diabetes and several other clinical conditions.

Maintaining optimum glycemic control is essential for everyone, particularly those with prediabetes or diagnosed diabetes. However, vitamin D levels also have a role to play in the risk and management of diabetes.

The recommendation is for everyone to get a 25 hydroxyvitamin D test, although particularly if you have diabetes, are at risk of diabetes, or are at risk of vitamin D deficiency.

People who stay indoors most or all of the time, are older adults, or cover their skin up are at an increased risk of vitamin D insufficiency.

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  2. Norman AW. From vitamin D to hormone D: fundamentals of the vitamin D endocrine system essential for good health. Am J Clin Nutr. 2008 Aug;88(2):491S-499S. doi: 10.1093/ajcn/88.2.491S. PMID: 18689389. Available at:
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  10. Thomas J. Littlejohns, William E. Henley, Iain A. Lang, Cedric Annweiler, Olivier Beauchet, Paulo H.M. Chaves, Linda Fried, Bryan R. Kestenbaum, Lewis H. Kuller, Kenneth M. Langa, Oscar L. Lopez, Katarina Kos, Maya Soni, David J. Llewellyn Vitamin D and the risk of dementia and Alzheimer disease Neurology, Sep 2014, 83 (10) 920-928. Available at:

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