A new study from the University of Eastern Finland found that taking large daily doses of vitamin D for five years did not lower the risk of getting type 2 diabetes in older adults.
The results come from the Finnish Vitamin D Trial, which followed nearly 2,500 men and women to see whether long-term use of high-dose vitamin D could help prevent diabetes.
Previous research has shown that people with low levels of vitamin D in their blood seem to have a higher chance of developing type 2 diabetes. But these earlier studies only showed a link, not whether taking vitamin D could actually stop the disease.
A few short-term experiments have found small benefits for people with prediabetes, which is when blood sugar is higher than normal but not yet in the diabetic range. However, no clear benefits were seen in people with normal blood sugar levels.
This new study aimed to find out whether long-term, high-dose vitamin D supplements could make a difference for people without blood sugar problems. Between 2012 and 2018, researchers enrolled 2,495 healthy older adults into the study.
The participants included men over 60 and women over 65. They were randomly divided into three groups: one group received a placebo (a pill with no active ingredient), one group received 40 micrograms of vitamin D3 per day, and the third group received 80 micrograms per day. That’s much higher than the daily recommended amount.
The researchers collected detailed information from the participants about their health, diet, and lifestyle. People who already had diabetes and were taking medication for it were excluded from the analysis, leaving 2,271 participants.
About 20% of the participants were also randomly selected for more detailed testing and had their blood levels of vitamin D measured.
After five years, 105 people in total developed type 2 diabetes: 38 in the placebo group, 31 in the lower-dose vitamin D group, and 36 in the high-dose group. These differences were small and not considered statistically meaningful. In other words, taking high doses of vitamin D did not reduce the risk of developing diabetes.
Among those who had their blood tested, most already had good levels of vitamin D before the study began. Only 9% had low levels. After one year of taking supplements, vitamin D levels increased in the groups receiving 40 and 80 micrograms per day, reaching average blood levels of 100 and 120 nmol/l respectively.
There was no major change in the placebo group. The researchers also looked at other measures like blood sugar, insulin, weight, and waist size over the first two years, but found no differences between the groups.
The main takeaway is that taking more vitamin D than recommended doesn’t help prevent type 2 diabetes in healthy older adults who already have good vitamin D levels. It’s still unclear whether high doses might help people who don’t have prediabetes but are vitamin D deficient. More research is needed to answer that question.
If you care about diabetes, please read studies about Potatoes: friend or foe in the battle against diabetes? and findings of This blood pressure drug may protect kidney health in people with diabetes.
For more about diabetes, please read studies about Scientists find a promising treatment for type 2 diabetes and findings of Certain type 2 diabetes treatment may bring heart risks.
The study is published in Diabetologia.
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