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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

Type II diabetes

woman swimming in pool

What is Type II diabetes?

Type II diabetes is a condition in which the body has a hard time managing blood sugar effectively. Usually one develops type II diabetes in adulthood, past the age of 40, but it has become increasingly common in children and teenagers. Once an individual develops type II diabetes, it usually lasts for the rest of their life.

Beta cells in the pancreas make a hormone called insulin, which helps shuttle the glucose that enters the bloodstream after a meal into the body’s tissue, especially liver and muscle tissues.

Insulin ensures that the body either uses or stores this glucose, helping manage glucose properly. People with type II diabetes (T2D) either don’t make enough insulin to help manage all of the glucose, or their body “ignores” the insulin they do produce, making it hard to manage all the glucose.

When glucose starts to build up in the blood stream instead of being used or stored, it can cause diabetes complications. Complications may include the following:

  • Eyesight issues
  • Skin conditions
  • High blood pressure
  • Nerve damage (neuropathy)
  • Kidney damage (nephropathy)

T2D usually occurs gradually. Often times, individuals are diagnosed with prediabetes, meaning their blood sugar levels are abnormally high, but not elevated enough to be considered diabetic. Fortunately, those diagnosed with prediabetes may return to normal blood sugar levels through modifying their lifestyle, such as exercising and reducing their weight.

Treatments for T2D require lifelong monitoring of sugar levels in one’s blood, healthy eating, regular exercising and possibly diabetes medication. Some people with T2D can manage their condition with diet and exercise alone, but many need additional help with medications.

How common is type II diabetes?

T2D has become more prevalent in recent years. In 2014, 9.3% of the US population has T2D, according to the Centers for Disease Control and Prevention. More than one million people are newly diagnosed in the United States annually.

What does type II diabetes feel like?

Symptoms of T2D often occur slowly. One can have T2D for years and not know it. Here are some symptoms one might have

  • Increased thirst and frequent urination: Excess sugar in one’s blood causes the body to release fluid.
  • Increased hunger: Without insulin to move sugars into the right places, the muscles and organs become tired, triggering increased appetite..
  • Weight loss: Without the ability to metabolize glucose for energy, the body uses other fuel sources stored in muscle and fat, causing weight loss.
  • Fatigue: When cells aren’t able to receive the sugar they need because of poor insulin function, the individual becomes lethargic and even short-tempered.
  • Vision problems: If the blood sugar is too high, fluid may be pulled from the lenses of one’s eyes, causing blurred vision.
  • Slow healing or frequent infections: T2D affects one’s ability to heal and fight off infection.
  • Patches of dark skin: Occasionally, people with T2D have areas of dark skin in the folds and creases of their bodies – like one’s armpits or neck – which can be a sign that one’s body is “resistant” to insulin.

If you has some of these symptoms, or one are concerned that one might have T2D, setup an appointment with your doctor.

What causes type II diabetes?

T2D occurs when the body stops producing enough insulin or the body becomes “resistant” to insulin. Insulin resistance means that the body doesn’t use insulin as much as it should. Exactly why this happens is not fully clear, although being overweight and a lack of physical activity seem to play a role.

Without enough insulin being used, the body doesn’t break down sugar into glucose. Then the cells don’t get the glucose they need. When the cells aren’t getting enough glucose, they don’t function properly and sugar builds up in the blood stream and can cause damage to multiple areas of the body, including the nerves and kidneys.

Some people are more likely to get T2D than others. Certain factors increase one’s risk of getting T2D, though it’s not fully understood why some of these factors increase one’s chances. Risk factors include:

  • Being overweight: The more fat tissue one has, the harder it is for one’s body to use insulin.
  • Weight distribution: If the body stores fat in the mid-section, one’s risk is greater than if extra fat is stored elsewhere.
  • Sedentary lifestyle: Physical activity helps control one’s weight, use glucose effectively and improve insulin sensitivity.
  • Family history: The risk increases if one has a family member with T2D.
  • Race: People of certain races, including African Americans, Hispanics, American Indians and Asian Americans, are more likely to develop T2D than Caucasian Americans.
  • Age: The risk of T2D increases with age, especially after age 45.
  • Prediabetes: Prediabetes is a condition in which one’s blood sugar levels are higher than normal, but not high enough to be diagnosed as diabetes. If one has prediabetes, this individual is at an increased risk of developing T2D.
  • Gestational diabetes: If one has developed gestational diabetes during pregnancy, this person is at an increased risk of T2D later in life.

Dietary risk factors include added sugars[1], simple carbohydrates[2], alcohol and saturated fats[3]. Processed foods often contain these dietary risks.

What is the link between vitamin D and type II diabetes?

Studies have shown that people who have the lowest vitamin D levels in their blood are at an increased risk of developing T2D.

In fact, studies have shown that people who have the lowest serum vitamin D levels are at an increased risk of developing T2D later in life. Research has also discovered that people newly diagnosed with T2D often have lower vitamin D levels than those without diabetes.

Doctors and scientists think that vitamin D may have a hand in T2D by playing a role in one’s pancreatic beta-cell function, insulin action and inflammation. Let us explain a little more:

Pancreatic beta cell function

When an individual has T2D, sometimes the beta cells in the pancreas that produce insulin don’t work properly. Researchers are interested in vitamin D because there are specific receptors in pancreatic beta cells that only start “turning-on” if they receive enough vitamin D. Therefore, researchers think that vitamin D can help one’s pancreatic beta cells function properly. Animal studies have been conducted where these vitamin D receptors were removed, resulting in a inadequate production of insulin.[4]

How our body uses insulin

When glucose is transported to the blood, the pancreas releases the hormone, insulin, which will bind to cell receptors and allow glucose to be transported into the cell. If one is sensitive to insulin, this individual doesn’t require very much insulin to help the body turn sugar into glucose, the body’s main source of energy.

On the other hand, people with T2D are “resistant” to insulin, meaning their bodies don’t use insulin very well. As blood glucose continues to rise, the cells become deprived of energy. In order to normalize blood sugar levels in those with T2D, they will require an abnormally large amount of insulin produced from the pancreas, or an insulin injection.

Researchers are interested in the role vitamin D plays in improving insulin sensitivity and increasing insulin secretion. Studies have reported a link between low vitamin D and decreased insulin sensitivity.[5],[6]

Furthermore, vitamin D plays an important part in the regulation of calcium. Calcium helps to control the release of insulin, so alterations in calcium can have a negative effect on beta cell function, which may hinder normal insulin release. Some scientists and doctors believe that if vitamin D helps proper insulin function, some of its effects might be because of calcium.

Can vitamin D prevent type II diabetes?

Several studies have looked at the role of vitamin D status in the incidence of T2D. There have been three recent reviews, where researchers looked at all the studies published on vitamin D and T2D, combined them, and determined if there was a connection between vitamin D and T2D.

  • A 2011 review looked at studies which examined how much vitamin D people were getting by measuring their vitamin D blood level or by administering a vitamin D supplement and then followed participants to see if they developed T2D later in life. They found that people with higher vitamin D blood levels (>25 ng/ml) had a decreased chance of developing T2D later in life compared to those with the lowest levels (<14 ng/ml).[7]
  • In a 2012 review, researchers looked at studies examining vitamin D status by measuring their vitamin D blood level. The researchers then followed participants to see if they got T2D later in life. People with the highest vitamin D blood levels had a 19% decreased risk of developing T2D compared to those with the lowest levels.[8]
  • In a 2013 review, researchers combined 18 studies which examined how much vitamin D people were getting by measuring their vitamin D blood level and then followed participants to see if they got T2D later in life. Participants with the highest vitamin D levels had a decreased risk of diabetes compared to those with the lowest vitamin D levels. Every 4 ng/ml increase in vitamin D was associated with a 4% lower risk of getting T2D later in life.[9]

However, these reviews mainly looked at studies that were observational, meaning we don’t know if low vitamin D caused T2D later in life or if low vitamin D was associated with some other unknown risk factor which caused T2D to develop later in life.

A recent trial in 2011 gave 2000 adults at high risk of T2D either 2000 IU of vitamin D per day or 400 mg calcium. They wanted to see if vitamin D helped improve symptoms associated with T2D compared to participants who didn’t get vitamin D. They found that vitamin D supplementation improved pancreatic B cell function – important for making insulin – and helped control the rise of blood sugar.7

However, another very recent trial found that vitamin D supplementation in people with pre-diabetes (higher than normal blood sugar levels) had no effect in reducing the risk of developing diabetes later. Furthermore, people who supplemented with vitamin D didn’t produce more insulin nor were they more sensitive to insulin than those taking a dummy pill. They were also just as likely to develop diabetes later in life as people taking the dummy pill.[10]

Can vitamin D improve certain aspects of type II diabetes?

People with T2D who were eating yogurt fortified with vitamin D and calcium had significantly lower blood sugar levels than people eating yogurt without vitamin D.

Researchers are interested in vitamin D for improving certain aspects of T2D. They want to know if getting enough vitamin D can help:

  • Reduce insulin resistance and improve sensitivity.
  • For people with T2D that don’t make enough insulin, if vitamin D can help one produce more insulin.

There have been a few trials that have looked if vitamin D can help in these aspects. Four trials report:

  • Among obese adolescents without diabetes, vitamin D supplementation of 4,000 IU/day improved how sensitive the participants were to insulin.[11]
  • People with T2D who were eating yogurt fortified with vitamin D (1000 IU/day) and calcium (600 mg/day) had significantly lower blood sugar levels, less inflammation, and increased glucose regulation – ensuring their body used the glucose as energy – compared to T2D participants eating yogurt without vitamin D.[12]
  • Researchers in New Zealand found that vitamin D supplementation improved insulin resistance and insulin sensitivity, but only if the dose was large enough and administered over a sufficient period of time.[13]
  • A two-year vitamin D supplementation trial involving African Americans with T2D found that raising vitamin D levels from 25 ng/mL to 34 ng/mL significantly reduced hemoglobin A1c from 9.15% to 7.98% .[14]

On the other hand, there are three small trials, which found that vitamin D supplementation in patients with T2D, didn’t significantly decrease blood sugar levels, regulate glucose management, and decrease insulin resistance. However, these trials were fairly small and had relatively short study lengths, making it hard to get a good picture if vitamin D had any effect (2-6 months).[15]

Key points from the research

  • People newly diagnosed with T2D tend to have lower vitamin D levels than people without T2D.[16]
  • A review of the research found that people with higher vitamin D levels have a decreased risk of developing T2D later in life compared to people with the lower levels.5
  • However, one randomized controlled trial found that vitamin D supplementation in people with pre-diabetes (higher than normal blood sugar levels) had no effect on insulin secretion, insulin sensitivity, or the development of diabetes when compared to a group of participants taking a dummy pill.4
  • We need more research before we can definitively say if vitamin D can help prevent T2D or not.
  • For people already with T2D, there is some evidence that vitamin D may help improve resistance to insulin, increase sensitivity to insulin, and more effectively control blood sugar levels. Still more research is needed to say definitively.

What does this mean for me?

There is currently some evidence that getting enough vitamin D may reduce one’s risk of developing T2D, although what are called large scale intervention studies are needed before we can say for sure.

There is intriguing research suggesting that supplementing with vitamin D may help improve some of the aspects associated with T2D. Studies have shown that vitamin D supplementation improves insulin sensitivity and decreased blood sugar levels. However, not all people with T2D see improvement in symptoms.

If one or someone one know has T2D, it’s unlikely that taking vitamin D will make one’s symptoms worse or cause any harm if one take 10,000 IU or less daily, although one may not see improvement in one’s T2D either.

In addition, spending time in the sun with a moderate amount of skin exposed daily when the sun is high enough that one’s shadow is shorter than one’s height will not only produce vitamin D but sunshine may also have other health benefits that are not yet well understood.

If one have T2D, it’s important to talk to one’s doctor about taking vitamin D or any other supplements. Don’t take vitamin D in place of any medications one are currently prescribed.

References

[1] DiNicolantonio, J.J., J.H. O’Keefe, and S.C. Lucan, Added Fructose: A Principal Driver of Type 2 Diabetes Mellitus and Its Consequences. Mayo Clin Proc, 2015 Mar;90(3):372-381.

[2] Hu, E.A., et al., White rice consumption and risk of type 2 diabetes: meta-analysis and systematic review. BMJ, 2012. 344: p. e1454.

[3] Forouhi, N.G., et al., Differences in the prospective association between individual plasma phospholipid saturated fatty acids and incident type 2 diabetes: the EPIC-InterAct case-cohort study. Lancet Diabetes Endocrinol, 2014. 2(10): p. 810-8.

[4] Zeitz, U., et al., Impaired insulin secretory capacity in mice lacking a functional vitamin D receptor. FASEB J, 2003. 17(3): p. 509-11.

[5] Scragg, R., M. Sowers, and C. Bell, Serum 25-hydroxyvitamin D, diabetes, and ethnicity in the Third National Health and Nutrition Examination Survey. Diabetes Care, 2004. 27(12): p. 2813-8.

[6] Chiu, K.C., et al., Hypovitaminosis D is associated with insulin resistance and beta cell dysfunction. Am J Clin Nutr, 2004. 79(5): p. 820-5.

[7] Mitri, J., et al., Effects of vitamin D and calcium supplementation on pancreatic beta cell function, insulin sensitivity, and glycemia in adults at high risk of diabetes: the Calcium and Vitamin D for Diabetes Mellitus (CaDDM) randomized controlled trial. Am J Clin Nutr, 2011. 94(2): p. 486-94.

[8] Khan, H., et al., Vitamin D, type 2 diabetes and other metabolic outcomes: a systematic review and meta-analysis of prospective studies. Proc Nutr Soc, 2013. 72(1): p. 89-97.

[9] Song, Y., et al., Blood 25-hydroxy vitamin D levels and incident type 2 diabetes: a meta-analysis of prospective studies. Diabetes Care, 2013. 36(5): p. 1422-8.

[10] Davidson, M.B., et al., High-dose vitamin D supplementation in people with prediabetes and hypovitaminosis D. Diabetes Care, 2013. 36(2): p. 260-6.

[11] Belenchia, A.M., et al., Correcting vitamin D insufficiency improves insulin sensitivity in obese adolescents: a randomized controlled trial. Am J Clin Nutr, 2013. 97(4): p. 774-81.

[12] Shab-Bidar, S., et al., Regular consumption of vitamin D-fortified yogurt drink (Doogh) improved endothelial biomarkers in subjects with type 2 diabetes: a randomized double-blind clinical trial. BMC Med, 2011. 9: p. 125.

[13] von Hurst, P.R., W. Stonehouse, and J. Coad, Vitamin D supplementation reduces insulin resistance in South Asian women living in New Zealand who are insulin resistant and vitamin D deficient – a randomised, placebo-controlled trial. Br J Nutr, 2010. 103(4): p. 549-55.

[14] Green, R.T., et al., Maintenance of long-term adequate levels of vitamin d lowers HbA1c in African American patients with type 2 diabetes. Ethn Dis, 2014. 24(3): p. 335-41.

[15] Mitri, J., M.D. Muraru, and A.G. Pittas, Vitamin D and type 2 diabetes: a systematic review. Eur J Clin Nutr, 2011. 65(9): p. 1005-15.

[16] Pittas, A.G., et al., Systematic review: Vitamin D and cardiometabolic outcomes. Ann Intern Med, 2010. 152(5): p. 307-14.

 This page was last updated January 2016.