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February 07, 2023

Vitamin D supplements may decrease diabetes risk in people with prediabetes, researchers say

Scientists are still not sure about the optimal dose, and warn that high levels can cause harm

Prevention Diabetes
Diabetes and vitamin D Michele Blackwell/Unsplash

Many experts warn that too much vitamin D can be harmful, so caution is needed when weighing the potential risks and benefits of the supplements.

The sunshine vitamin, vitamin D, is important for our bone health. But new research suggests that boosting vitamin D levels may also reduce the risk of type 2 diabetes in people with prediabetes.

In an analysis of three clinical trials, researchers from Tufts Medical Center in Boston found that vitamin D supplements offered modest protection against full blown diabetes in patients with prediabetes. Study participants were either given a vitamin D supplement or placebo pills. A little under 23% of those in the supplement group developed diabetes within three years compared with 25% of those given the placebo.

The researchers calculated that the supplements lowered the risk of diabetes progression by 15% in people with prediabetes. They emphasized though that this risk reduction was found in people at high risk of type 2 diabetes, it doesn't apply to people at average risk.

On their own, the three clinical trials analyzed didn't produce a significant difference in risk between the supplement and placebo groups. With a large number of patients across all three trials, however, they saw a moderate benefit. Just over 4,000 adults with pre-diabetes were included in the meta-analysis.

Lead researcher Dr. Anastassios Pittas and his team were unable to determine the optimal dose of the vitamin for people with prediabetes.

A lack of vitamin D has been linked to various health conditions, including cardiovascular disease, type 2 diabetes, cancer, multiple sclerosis, depression and dementia. Previous studies have suggested vitamin D supplements may help reduce the risk of cancer and heart disease – and slow their progression.

But according to the Mayo Clinic, too much vitamin D can lead to a buildup of calcium in the blood which can cause nausea, vomiting, weakness and frequent urination. When vitamin D toxicity continues, it could lead to bone pain and kidney problems including kidney stones.

Experts emphasize that lifestyle changes such as healthy diet and exercise are still necessary to reduce the risk of type 2 diabetes. Vitamin D supplementation is not a panacea.

Dr. Isaac Dapkins, chief medical officer of NYU Langone's Family Health Centers in New York City, told U.S. News & World Report the findings suggest the important of testing vitamin levels in patients with prediabetes. He was not involved in the study.

In an accompanying editorial to the study, authors from University College Dublin and the Food Safety Authority of Ireland highlight that previous data have demonstrated significant adverse effects of high vitamin D intake. They wrote that professional societies promoting vitamin D therapy have an obligation to ensure physicians are aware of both required vitamin D intake and safe limits. They emphasized that very-high-dose vitamin D therapy might prevent type 2 diabetes in some patients but it may also cause harm.

Type 2 diabetes occurs when the body develops a resistance to insulin, a hormone that helps regulate blood sugar. Because cells no longer respond to insulin, the pancreas tries to make more. But that in turn causes blood sugar rise to dangerous levels.

Left untreated, type 2 diabetes can lead to heart disease, vision loss and kidney disease. Symptoms include increased thirst and urination, unexplained weight loss, blurred vision and fatigue.

Prediabetes is a precursor to type 2 diabetes that affects about 96 million Americans, according to the CDC. This condition occurs when blood sugar levels are elevated, but not at a high enough level for a person to be considered a diabetic. Prediabetes also increases your risk of heart disease and stroke.

Previous studies have found that diabetes is more prevalent in places farther from the equator, suggesting a link between limited sunshine and the disease. When your skin is exposed to sunlight, it triggers the natural production of vitamin D. Upon further investigation, scientists began to observe that lower levels of vitamin D were associated with a higher risk of type 2 diabetes.

While it is not completely clear why this is, animal studies suggests that vitamin D can restore normal insulin production. 

Besides sunshine, vitamin D is found in fortified milk and cereals, egg yolks and fatty fish such as salmon, mackerel and sardines. If you are concerned about your vitamin D levels, talk to your health care provider about getting evaluated.

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