Many doctors recommend vitamin D serum levels of 20-30 nanograms per milliliter (ng/mL)—but for people with prediabetes, that may not be enough. A recent study found that vitamin D serum levels of 40 ng/mL or higher were linked to protective effects against the development of diabetes.¹ To achieve an optimal level, higher doses of vitamin D may be needed, according to the study's authors. (Life Extension's optimal vitamin D range is 50 to 80 ng/mL.)

The study analyzed data from 2,362 prediabetic men and women who participated in a trial that examined the association between intake of 4,000 IU of vitamin D and the risk of developing diabetes. Serum 25-hydroxyvitamin D levels were measured prior to a 2.5-year median follow-up period and were repeated each year.

In addition to looking at vitamin D serum levels and diabetes, researchers set out to determine whether overweight or obese prediabetics and people of color with prediabetes have different associations between vitamin D levels and diabetes risk compared with normal weight or Caucasian prediabetics. The conclusion? While both groups benefited from vitamin D intake, Whites benefitted more. Caucasian and Black participants whose average annual vitamin D levels measured during the trial were 40 ng/mL or higher had significantly lower risks—58% and 49% lower, respectively—of developing diabetes than those whose levels were 20 ng/mL to less than 30 ng/mL. A serum vitamin D level of 40 ng/mL or more was also significantly protective for participants who had body mass indexes of less than <40 kg/m2. The findings were published on March 29, 2023, in the American Journal of Clinical Nutrition.

Similar findings in a recent review and meta-analysis published in the Annals of Internal Medicine suggested that high vitamin D levels may be optimal for diabetes prevention.² The review found that vitamin D intake overall reduced the risk for diabetes by 15%. In those in the vitamin D group who maintained a serum 25-hydroxyvitamin D level of at least 50 ng/mL during the trial, compared with 20 to 29 ng/mL, relative risk of diabetes risk was reduced by 76%. Vitamin D intake conferred a 30% chance of restoring normal glucose regulation. Vitamin D was well-tolerated, with no increased risk of adverse events.