Key Points
- A five-year study found that taking high doses of vitamin D does not lower the risk of type 2 diabetes in older adults with normal blood sugar levels.
- Participants taking 40 or 80 micrograms (mcg) of vitamin D daily showed no significant differences in diabetes incidence compared to a placebo group.
- The study highlights the need for more research on the potential benefits of vitamin D in people with low levels or prediabetes.
In elderly men and women, taking significantly higher doses of vitamin D than recommended for five years did not affect the risk of developing type 2 diabetes, according to a new study from the University of Eastern Finland.
The link between vitamin D and type 2 diabetes risk
Type 2 diabetes is characterized by high blood glucose (sugar), insulin resistance, and insufficient insulin production. In previous observational studies, low levels of vitamin D have been linked to a higher risk of type 2 diabetes. However, because observational studies only collect data without intervening in participants’ behaviors, they cannot prove whether taking vitamin D supplements can directly lower the risk of the condition.
Other studies have indicated that the use of significantly higher doses of vitamin D than recommended slightly reduces the risk of type 2 diabetes in people with prediabetes (a condition in which blood sugar is higher than normal, but not high enough for a diagnosis of diabetes). These earlier studies, however, often used smaller doses of vitamin D or were limited to short-term investigations.
Until now, no studies had looked at how taking high doses of vitamin D for a long time affects the risk of developing type 2 diabetes in people with normal blood sugar levels.
What the study looked at
For the Finnish Vitamin D Trial (FIND), conducted from 2012 to 2018, 2,495 men ages 60 and older and women ages 65 and older were randomly assigned to receive either a placebo (inactive treatment), 40 mcg of vitamin D3 per day, or 80 mcg of vitamin D3 per day. (The Institute of Medicine recommends 15 mcg [600 IU] of vitamin D daily in adults 19 to 70 years of age and 20 mcg [800 IU] daily in adults ages 71 years and up.) Participants were generally healthy older adults with good baseline vitamin D levels.
Data on 224 people who were using diabetes medications at the start of the study was excluded. Researchers collected information from the remaining participants on their lifestyle, nutrition, diseases, and other risk factors, and details were also collected from national health registers. Roughly one-fifth of the participants were randomly selected for more detailed examinations and blood samples.
Key findings from the study
Over the course of the five-year study, 105 people developed type 2 diabetes: 38 in the placebo group, 31 in the group taking 40 micrograms of vitamin D3 daily, and 36 in the group taking 80 micrograms of vitamin D3 daily. There was not a statistically significant difference in the number of diabetes cases between these groups.
In the 505 participants selected for closer study, the blood calcidiol level (which indicates the amount of vitamin D in the blood) was low — below 50 nmol/l — in only 9% of participants. The level was, on average, 75 nmol/l at the start of the study. After one year, the average levels were 100 nmol/l in the group receiving 40 mcg of vitamin D and 120 nmol/l in the group receiving 80 mcg. Levels in the placebo group did not change significantly.
The impact of vitamin D on blood sugar, insulin levels, body-mass index (a measurement of weight relative to height), and waist circumference were investigated during the first two years of the study, but no differences were seen.
“The findings of the FIND study reinforce the view that the use of higher doses of vitamin D than recommended does not significantly affect the risk of developing type 2 diabetes in individuals without prediabetes and who already have a good vitamin D status. So far, there is no research data on whether high doses of vitamin D can be beneficial in preventing type 2 diabetes in individuals without prediabetes but with vitamin D deficiency.”
More research is needed on vitamin D and diabetes
This highlights the need for further research to understand how vitamin D supplementation might affect different populations, particularly those with lower vitamin D levels.
As researchers continue to explore the relationship between vitamin D and diabetes, understanding your vitamin D status and consulting a healthcare provider can be helpful steps toward managing your health.
For more information, read the press release from the University of Eastern Finland or see the study in the journal Diabetologia.
Want to learn more about vitamin D and diabetes? Read “Get to Know Vitamin D.”
