Taking high doses of vitamin D for several years does not lower the risk of developing type 2 diabetes in older adults, according to a new study from the University of Eastern Finland.
The research shows that even when vitamin D is taken at levels much higher than recommended, it does not prevent diabetes in people who already have healthy vitamin D levels and no signs of prediabetes.
Past studies have shown that people with low vitamin D levels may be more likely to develop type 2 diabetes. However, these studies were observational, meaning they couldn’t prove whether taking vitamin D supplements actually reduces the risk.
Some clinical studies have found a slight benefit in people with prediabetes who took high doses of vitamin D. But for people without problems in glucose metabolism, no clear benefit has been shown—especially when lower doses or shorter study periods were used.
The new findings come from the Finnish Vitamin D Trial (FIND), which took place from 2012 to 2018. In this trial, researchers followed 2,495 participants—men aged 60 and older and women aged 65 and older—for five years. The participants were randomly assigned to take a placebo, 40 micrograms of vitamin D3 per day, or 80 micrograms per day.
To focus on those without diabetes, the researchers excluded 224 people who were already using diabetes medications when the study began. Throughout the trial, participants provided detailed information on their lifestyle, diet, medical history, and risk factors.
The researchers also used national health records and took blood samples from a randomly selected group of about one-fifth of the participants for more in-depth analysis.
After five years, 105 participants developed type 2 diabetes: 38 from the placebo group, 31 from the 40-microgram group, and 36 from the 80-microgram group. The differences between these groups were not statistically significant, meaning vitamin D did not appear to have a real effect.
In the more closely monitored group of 505 people, the average vitamin D level (measured by blood calcidiol) was 75 nmol/l at the start of the study. Only nine percent had low levels below 50 nmol/l.
After one year, those taking 40 micrograms of vitamin D had average levels of 100 nmol/l, while those taking 80 micrograms reached 120 nmol/l. There was no change in the placebo group. Despite these increases in vitamin D levels, there were no changes in blood sugar, insulin, body weight, or waist size during the first two years.
The results suggest that taking high doses of vitamin D does not reduce the chance of getting type 2 diabetes in older adults who do not already have glucose metabolism problems and who have adequate vitamin D levels.
So far, researchers don’t know whether high doses might help people without prediabetes but who have a vitamin D deficiency. More research is needed to explore that possibility.
If you care about diabetes, please read studies about diabetes and vitamin B12, and the right diet for people with type 2 diabetes.
For more health information, please see recent studies about how to eat smart with diabetes, and turmeric and vitamin D: a duo for blood pressure control in diabetic patients.
