February 23, 2011
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: http://bit.ly/ebYb02 American Journal of Clinical Nutrition, online February 2, 2011.
February 22, 2011
Study sees no link between vitamin D, diabetes
NEW YORK (Reuters Health) - Low levels of vitamin D don't put older women at greater risk for type 2 diabetes, a large study of U.S. women suggests.
The findings may further temper the enthusiasm for vitamin D that built up in recent years, as studies linked it to lower risks of everything from diabetes, to severe asthma, heart disease, certain cancers and depression.
"You can't make dietary recommendations based on observational studies," said Dr. Jennifer G. Robinson of the University of Iowa and the lead researcher on the new study.
In an interview with Reuters Health, she pointed to the recent report on vitamin D from the Institute of Medicine (IOM), which said the evidence didn't show that vitamin D has any health benefits beyond building and maintaining strong bones.
It also said average Americans already have healthy serum levels of 25(OH)D.
The new study, in Diabetes Care published online February 2nd, involved women participating in the Women's Health Initiative, a large government project that looked at the health effects of hormone therapy, diet changes, and vitamin D and calcium supplements on a racially and ethnically diverse population of postmenopausal women.
Of 5,140 women who were free of type 2 diabetes at the start of the trial, 6.2% developed the disorder over an average of 7 years.
Dr. Robinson's team found no clear link between the women's blood levels of vitamin D at the outset and their risk of developing type 2 diabetes later on.
Initially, there was some evidence of an association. But it disappeared when the researchers accounted for factors like body weight, exercise levels and certain diet habits, like fiber intake -- which are key in the risk of developing type 2 diabetes.
"Look at how you get vitamin D," Dr. Robinson said. She noted that the main sources include sun exposure, fatty fish like salmon and mackerel, and vitamin D-fortified dairy products. "People who get those things are a lot different from people who don't."
And it's those factors, Dr. Robinson said, that may account for the link between vitamin D and lower diabetes risk researchers thought they had found in older studies.
Still, the current study, like past ones, was observational.
A large, government-sponsored randomized trial is currently underway. It will involve 20,000 U.S. adults who are randomly assigned to take vitamin D, omega-3 fatty acids (together or alone) or placebo.
The IOM recommends that adults in their 70s and up get 800 IU of vitamin D per day, while everyone else older than 12 months should get 600 IU.
SOURCE: http://bit.ly/i8h4fL
Diabetes Care 2011.
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