Vitamin D may help keep blood sugar under control
NEW YORK (Reuters Health) - Drinking yogurt with extra vitamin D may help people with diabetes regulate their blood sugar, a study from Iran finds.
In the trial, 90 adults with diabetes were divided into three groups, all given daily yogurt drinks: one group received plain yogurt, one got yogurt with extra vitamin D, and one was given yogurt with extra vitamin D and calcium.
At the end of 12 weeks, "we found a relatively remarkable improvement" in blood sugar levels in the groups that got extra vitamin D, compared to the plain yogurt group, co-author Tirang Neyestani, associate professor at National Nutrition and Food Technology Research Institute in Iran, told Reuters Health in an e-mail.
Past studies on the role of vitamin D in diabetes have not been able to show cause and effect.
It's noteworthy that this study does, and that it suggests vitamin D has a positive effect on people with type 2 diabetes, said Dr. Anastassios Pittas, assistant professor of medicine at Tufts University School of Medicine in Boston. He was not part of the study.
In type 2 diabetes, the most common form of the disease, the body has trouble using insulin to process glucose from foods, resulting in excessive levels of the sugar in the bloodstream. Vitamin D is thought to help regulate the body's sensitivity to insulin and possibly insulin production by the pancreas.
Going back to the 1980s, numerous studies have linked vitamin D to a lowered risk of diabetes, however others have found no benefit. A recent report showed no link between women's blood levels of vitamin D and their risk of developing type 2 diabetes, for example. (See Reuters Health story of February 22, 2011.)
Few studies have directly tested the theory by giving people vitamin D and then seeing how they compare over time in diabetes-related measurements with similar subjects who did not consume the vitamin.
In the new study, 55 women and 35 men were divided into groups of 30, and all drank their assigned yogurt twice a day. The plain yogurt contained150 milligrams of calcium, the vitamin D-fortified yogurt had 500 international units (IU) of vitamin D and 150 milligrams of calcium, and the doubly-fortified yogurt contained 500 IU of vitamin D and 250 milligrams of calcium.
After three months, the plain yogurt group's average blood sugar increased from 187 to 203 milligrams per deciliter of blood (mg/dL). In both the fortified-yogurt groups, blood sugar dropped from 184 to about 172 mg/dL. Blood sugar levels above126 mg/dL are considered to be diabetic.
It's odd that the blood sugar of those who didn't receive extra vitamin D got worse, Pittas said. This could make it seem that the improvement in the vitamin D-fortified group was greater than it actually was, overstating the finding.
The plain-yogurt group also had an increase in hemoglobin A1C, a sign of raised blood sugar levels over time, while both vitamin-D groups' A1C numbers decreased.
In addition, people who got the fortified yogurt lost an average of two to five pounds during the study, while the plain-yogurt group stayed about the same.
Although this difference may seem small, it may have affected the participants' blood sugar levels, Pittas said.
"Weight loss by itself, regardless of what causes it, can improve diabetes," he told Reuters Health.
It's also important to note that the vitamin D was given in yogurt, instead of as a supplement, Pittas said, and taking the vitamin alone might produce different results.
Yogurt contains probiotics, the good bugs that help us digest food, and "there is some evidence that these may also be important in diabetes," Pittas explained.
The study, published in American Journal of Clinical Nutrition, was funded by the National Nutrition and Food Technology Research Institute in Iran. The yogurt was donated by the Dairy Industries of Iran, and was a substitute for the equivalent amount of dairy in the participants' normal diet.
People with type 2 diabetes should follow the current Institute of Medicine vitamin D recommendation of about 600 IU a day, Pittas said.
The study is "a little bit of a 'too good to be true' observation," he added, but it does "provide additional evidence for more, longer-term studies. I would not say that we should all be eating yogurt with extra vitamin D yet."
SOURCE: bit.ly/ebYb02 American Journal of Clinical Nutrition, online February 2, 2011.