Lindsey Desoto is a licensed, registered dietitian and experienced medical writer.
Isabel Casimiro, MD, is board-certified in internal medicine and works as an endocrinologist at the University of Chicago.
Interest in vitamin D and its role in the prevention and treatment of diabetes has grown tremendously over the past two decades. Despite many studies showing a connection between vitamin D and diabetes, uncertainty of vitamin D’s effects still exists.
This article will explore available research surrounding vitamin D and type 2 diabetes and how to ensure you get enough of this important vitamin.
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The belief that vitamin D status may influence the development of type 2 diabetes seems reasonable. Low vitamin D levels have been linked to high levels of inflammatory markers, impaired pancreatic beta-cell function (cells that make insulin), and insulin resistance (when your body’s cells don’t respond well to insulin and can’t take up enough glucose to use for energy)—all of which can lead to type 2 diabetes.
While observational studies suggest that individuals with low vitamin D levels are more likely to develop type 2 diabetes, research remains mixed on whether vitamin D supplementation lowers the risk of diabetes.
In an extensive study, researchers followed 2,423 adults at high risk for diabetes for an average of 2.5 years. Half of the participants were provided 4,000 international units (IU) of vitamin D supplementation, and the others were given a placebo (an identical pill that did not contain vitamin D). The research found:
Another review of studies found that vitamin D supplementation may delay the development of diabetes in people with prediabetes and vitamin D deficiency. However, no benefit was seen in those with normal vitamin D levels.
Research suggests that individuals with type 2 diabetes often have a vitamin D deficiency. One study noted people with type 2 diabetes and vitamin D deficiency are more likely to have inflammation and a higher hemoglobin A1c (A1C) than those who do not have a deficiency. The reversal of vitamin D deficiency could improve this population’s insulin secretion and A1C levels.
A review of 29 trials found no noticeable differences in fasting blood glucose levels, but a significant reduction in A1C after vitamin D supplementation was observed. Participants who were deficient in vitamin D experienced more significant reductions in A1C.
In another study, participants with type 2 diabetes who took a vitamin D supplement with the antidiabetic drug metformin had lower A1C levels over three and six months compared to those who only took metformin. Researchers called for further investigation to determine the optimal dose of vitamin D in people with type 2 diabetes.
Although research on vitamin D and diabetes remains inconclusive, vitamin D has many health benefits for the body. The most important is its ability to help your body absorb calcium, which is essential for normal bone mineralization.
In children, a vitamin D deficiency can cause the rare disease known as rickets, which can lead to delayed growth, bowed legs, and weakness due to softening of the bones. In teens and adults, vitamin D deficiency can cause osteomalacia (a softening of the bones) that also causes muscle weakness and bone pain. Long-term deficits in vitamin D and calcium can lead to osteoporosis (a condition of weak or brittle bones).
Your nerves and muscles also need vitamin D to function, and your immune system needs vitamin D to fight viruses and bacterial infections.
Studies have found that long-term vitamin D deficiency may lead to inflammatory diseases, including the autoimmune conditions rheumatoid arthritis and lupus, as well as inflammatory bowel disease (IBD). However, more research is needed to confirm this.
The amount of vitamin D a person needs daily to prevent a deficiency depends on age. Current daily recommended dietary allowances for vitamin D are:
Most adults can safely consume up to 4,000 IU daily. The best way to prevent vitamin D deficiency is to ensure you get adequate amounts of vitamin D from the foods you eat, dietary supplements, and sun exposure.
Foods that contain vitamin D include:
Foods fortified with vitamin D provide most of the vitamin D in your diet. These include:
Although the sun is your best source of vitamin D, it can be challenging to meet your daily needs this way, especially during the winter. People with dark skin and older adults may also struggle to get enough vitamin D because their skin doesn't make enough of it when exposed to sunlight.
If you suspect a vitamin D deficiency, your healthcare provider can order a simple blood test to check your vitamin D levels.
Vitamin D is necessary to help your body absorb calcium. It also affects your immune, muscle, and nervous systems. While several observational studies suggest that vitamin D may play a role in treating and preventing type 2 diabetes, more research is still needed.
The potential benefit of vitamin D supplementation appears to be more significant among individuals with a confirmed vitamin D deficiency. Some food, sunlight, and supplements are good sources of vitamin D.
When it comes to preventing and managing type 2 diabetes, the best way to do so is by making lifestyle changes, including exercising, following a nutritious diet, and maintaining a healthy weight. Given that there are no official guidelines for using vitamin D supplements to prevent or treat type 2 diabetes, it's essential to speak with your healthcare provider before adding these supplements to your diet.
Research on vitamins and supplements for diabetes is inconclusive. Unless you have a confirmed nutrient deficiency or your healthcare provider recommends adding a specific vitamin to your supplement regimen, it's unlikely to be helpful.
There is no established dose of vitamin D recommended for people with diabetes. The recommended daily amount of vitamin D is 600 IU for individuals ages 1 to 70 and 800 IU for those over 70.
It is believed that vitamin D plays a role in blood sugar regulation because it boosts insulin secretion through the vitamin D receptor on pancreatic beta cells. Vitamin D can also reduce insulin resistance through its receptors in the liver and muscles.
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Lindsey Desoto is a registered dietitian with experience working with clients to improve their diet for health-related reasons. She enjoys staying up to date on the latest research and translating nutrition science into practical eating advice to help others live healthier lives.
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