Researchers from Ben-Gurion University of the Negev-Soroka Medical Center and Nuclear Research Center Negev, Israel, wondered if both red and white wine might improve glucose control, depending on alcohol metabolism and genetic profiling.
Previous research has suggested that ethanol (alcohol) is the key, meaning that alcoholic drinks other than red wine could be equally beneficial; others claim that red wine has particularly advantageous properties.
People with diabetes have a higher risk of developing cardiovascular disease, as well as lower levels of "good" HDL cholesterol. High levels of HDL cholesterol can reduce the risk for heart disease and stroke, as it absorbs cholesterol and carries it back to the liver, where it is flushed from the body.
The researchers wanted to find out what the cardiometabolic effects would be when patients with type 2 diabetes took up drinking moderate amounts of alcohol; they also wanted to assess whether the type of wine would matter.
They hypothesized that initiating moderate wine consumption would lower cardiometabolic risk, mainly because of the ethanol component. They predicted similar effects of red and white wine. Because of genetic variability in alcohol metabolism, they predicted that the effects of wine would vary according to ADH1B genotype.
The 224 participants were 40-75-year-old alcohol-abstaining men and women with well-controlled type 2 diabetes.
Among those excluded were: people already taking more than one alcoholic drink per week, anyone with a history of addiction and patients using two or more insulin injections a day.
Measurements taken at baseline included genetic markers, blood pressure, liver biomarkers, medication use and symptoms, and quality of life.
From June 2010 to May 2012, participants were randomly assigned to 150 mL of mineral water, white wine or red wine with dinner. Wines and mineral water were provided. All groups followed a Mediterranean diet without caloric restriction. At intervals, blood samples were taken, questionnaires completed and group sessions attended.
Lipid and glycemic control profiles were primarily measured. Secondary outcomes included triglyceride levels, blood pressure, waist circumference, genetic interaction, medication use, liver function tests and quality-of-life indicators.
After 2 years, no material differences were identified across the groups in blood pressure, adiposity, liver function, drug therapy, symptoms or quality of life, except that sleep quality improved in both wine groups compared with the water group.
However, patients who drank wine showed decreased cardiometabolic risks compared with those drinking mineral water. The red wine drinkers experienced the most significant changes in lipid variables.
The researchers unexpectedly found that while the alcohol itself appears to aid glycemic control, red wine has a stronger effect on lipid levels and overall variables of the metabolic syndrome, suggesting that its non-alcoholic constituents also play a role.
The red wine had seven times higher levels of total phenols than the white wine. Whether the phenolic compounds increase the cardioprotectiveness is still debated. The team calls for differences between red and white wine to be further studied, with focus on the varied biodeliverability of the compounds.
The team found that genetic differences affected glycemic control and therefore suggest that genetic information could assist in identifying which patients with type 2 diabetes would benefit from moderate wine consumption.
Limitations include the participants not being blinded to treatment allocation, but the long-term nature of the study is a strength.
The authors caution that the benefits of drinking wine should be weighed against potential risks when translated into clinical practice.