By Sheryl Huggins Salomon
Though more research is needed, an observational study on about 900 healthy, mostly white older adults suggests that the more vitamin D you take in, the lower your risk of the disease.
Previous research suggests that having deficient levels of vitamin D may increase the risk of type 2 diabetes, and study results released this month seem to support that association.
The study, which was published in the April edition of PLoS One, followed 903 healthy adults for 12 years and found that those with lower amounts of vitamin D in their blood had a higher risk of developing type 2 diabetes over the course of the study.
Results of the study led researchers to conclude that getting enough vitamin D reduces the chance that a person will develop the disease. “The person that takes enough vitamin D3 has only one-fifth the risk of type 2 diabetes” as someone who does not get enough of the vitamin, says one of the study's coauthors, Cedric F. Garland, PhD, an adjunct professor at the University of California in San Diego School of Medicine. “Yet, probably 90 percent of the population is deficient in having their vitamin D at a level to prevent diabetes,” Dr. Garland says.
The body makes vitamin D3 when skin is exposed to sunlight, but the vitamin is also available in supplement form. Note that certain foods, like fortified yogurt and sardines, also contain vitamin D, but diet isn’t a primary source of the vitamin.
A January 2011 article in the Journal of Clinical Endocrinology & Metabolism notes that the Institute of Medicine (IOM) recommends taking no more than 4,000 international units (IU) of vitamin D per day. But Garland argues that people need a bit more — 5,000 IU per day — so their blood levels of 25-hydroxyvitamin D, which the liver produces during vitamin D processing, reach what he says is a sufficient amount, of 50 nanograms per milliliter (ng/ml). (The IOM recommends 20 ng/ml as a sufficient level for most people, according to the 2011 article.)
Vitamin D is key for calcium absorption, and getting enough of the vitamin can help build strong bones and teeth, reduce inflammation, and affect immunity, according to the National Institutes of Health (NIH). A review published in March 2016 in the World Journal of Diabetes suggests vitamin D deficiency is associated with chronic diseases including vitamin D, heart disease, kidney disease, hypertension, and cancer, but authors concluded that more clinical trials are needed. The NIH also points out that there isn’t enough data to suggest that sufficient vitamin D levels prevent any chronic disease except for those related to the bones, such as osteoporosis and osteomalacia.
The researchers set 30 ng/ml as the minimum healthy level of 25-hydroxyvitamin D in blood plasma, which is 10 ng/ml above the level recommended by the IOM. Any participant with a reading below that threshold was deemed vitamin D deficient. Study participants whose blood levels of 25-hydroxyvitamin D that were above 30 ng/ml were found to have an incidence of type 2 diabetes one-third that of people with 25-hydroxyvitamin D levels below that level.
The study population consisted of healthy adults with a mean age of 74 who were living in Southern California. Participants had no indications of either prediabetes or diabetes during clinic visits from 1997 to 1999, after which the researchers followed them through 2009. Researchers measured their blood levels of 25-hydroxyvitamin D, their fasting plasma glucose (a blood sugar test taken after fasting for at least eight hours) and their oral glucose tolerance (which measures the body’s response to ingesting sugar), during clinical visits. Authors accounted for participants’ vitamin D supplementation. Over the study period, they reported 47 new cases of diabetes and 337 new cases of prediabetes among the study group.
The authors pointed out that the cohort skewed toward white participants, a group that a study published in January 2011 in Nutrition Research suggests is less likely to face vitamin D deficiency than black and Hispanic people. Per an article published in December 2014 in Current Diabetes Reports, other research shows Hispanic and Native American people are at a higher risk of developing type 2 diabetes.
Study participants also tended to be older, and, as the American Diabetes Association notes, the prevalence of type 2 diabetes increases with age. But Garland says it made sense to study people in the age range that is more likely to experience diabetes, and there’s no reason to believe the finding that vitamin D deficiency is linked to a higher rate of type 2 diabetes would not apply to nonwhites as well. The fact that the study locale is sunny helped increase the chances that participants would have sufficient levels of 25-hydroxyvitamin D in the blood for authors to observe, he says.
Rahil Bandukwala, DO, an endocrinologist at MemorialCare Saddleback Medical Center in Laguna Hills, California, says that while he recommends vitamin D supplements to his patients, he thinks further research is needed on the relationship between deficiency of the vitamin and type 2 diabetes risk. “What I’d love to see is a randomized controlled study, perhaps looking at two populations, where you supplement vitamin D in one of them [and not the other], and then you follow them all over a period of time and look at incidence of type 2 diabetes and other conditions.”
Garland says he would be interested in future research on the link between vitamin D deficiency and diabetes risk in a more ethnically diverse population, but he advises against waiting to add more vitamin D to your diet, re-emphasizing that people with more pigment in their skin are at a greater risk of deficiency. You’ll want to talk to your doctor before adding a new supplement to your diet — especially if you’re on any medications — but according to the Mayo Clinic, vitamin D toxicity (called hypervitaminosis D) is rare. A vitamin D supplement "is very likely to help them and unlikely to hurt them,” Garland says.