By Brenda Goodman, MA
WebMD Health News
Reviewed by Brunilda Nazario, MD
Oct. 12, 2015 -- Should you have a glass of wine with dinner?
Science has what can seem like a million different answers for this question. If you're a woman under 45, the answer might be no -- a daily drink could raise your risk of breast cancer. But if you're a man in your 60s, the evidence is mixed. Some studies show it might be good for men's hearts, while other, more recent studies suggest there's no benefit from moderate drinking.
Throw a chronic condition into the mix, like diabetes, and the answers are even more confusing. Alcohol can lower blood sugar, which might seem like a good thing -- unless you drink too much. In that case, drinking can cause an episode of dangerously low blood sugar.
Beyond blood sugar, there's been limited evidence that moderate drinking might improve heart health. If true, that's important since people with diabetes are two to four times more likely to have heart disease.
That's why a new study is a standout. It found that having a daily glass of red wine modestly improved some measures of heart health.
Researchers were precise when they designed the study, including only men and women between the ages of 40 and 75 with stable, type 2 diabetes -- they couldn't need more than two insulin injections a day or be on an insulin pump. People were also excluded if they smoked or had a history of heart attack, stroke, or a recent major surgery.
They also did something that's unusual for alcohol studies: They randomly assigned 224 people to drink a glass of red or white wine or water with dinner every day for 2 years. That's the longest any group has been followed for this kind of test.
They were also a little sneaky. When they were recruiting for the study, they didn't tell people they were going to test the health effects of alcohol. Instead, they told them they would be eating a healthy, Mediterranean diet. They wanted to find people who abstained from alcohol as a general rule.
The result is that they were able to test the effects of drinking the same way pharmaceutical companies test drugs: using the gold standard of medical evidence, a randomized, controlled trial.
"We don't have really clear guidelines regarding moderate alcohol consumption, especially for type 2 diabetes, because there is a lack of long-term, randomized, controlled trials," says study researcher Iris Shai, PhD, a professor of nutrition at Ben-Gurion University of the Negev in Israel.
The study appears in the Oct. 13 issue of Annals of Internal Medicine.
Red wine drinkers saw their levels of HDL, or "good" cholesterol, rise by about 2 milligrams per deciliter (mg/dL) compared to the water drinkers. That's not a huge amount, but it was statistically significant, which means it was unlikely to have happened by chance. No such luck for the white wine drinkers, however.
Shai says that's probably because the red wine had about seven times as many beneficial compounds called phenols as the white wine did.
And both kinds of wine lowered morning insulin levels, but only in the people who carried a version of a gene that slowed down the time it took their bodies to break down alcohol. These so-called "slow metabolizers" had better blood sugar control than the 1 in 5 people in the study who were classified as "fast metabolizers" because they didn't carry a copy of that gene.
Fast metabolizers, on the other hand, saw improvements in their blood pressure where others did not.
Most importantly, there were no bad effects of drinking a glass of wine a day, and wine drinkers said they slept better compared to water drinkers.
Shai says this study adds some powerful new information for type 2 diabetes patients and doctors to consider.
"We found that on top of a healthy diet there is some beneficial effect for wine, and especially for red wine," Shai says. "We didn't expect to see a difference between red and white wine. That surprised us."
Shai says the bottom line is that if your diabetes is under control, drinking a little red wine -- meaning one glass a day -- seems to be safe and may slightly decrease risks to your heart's health.
One doctor who wasn't involved in the study said it was interesting and would probably change how she counsels diabetes patients.
"It's important to note that this was in the context of the Mediterranean diet. That's a very high-fiber diet, and it might have been a change for a lot of these people," says Suzanne Steinbaum, DO, a preventive cardiologist at Lenox Hill Hospital in New York City.
"I'm not sure I'm going to say to every diabetic patient, 'Have a glass of wine.' I might say to every diabetic, 'It really is important to be on the Mediterranean diet, and if you happen to have a glass of wine, it's OK,'" Steinbaum says.
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