At the end of a long week, people are opening wine bottles in bars, restaurants and homes around the world, ready to kick back and relax.
This relationship with wine has a long history. The oldest known winery, dating to 4100 B.C., was discovered in 2010 by archaeologists in an Armenian cave. Just recently scientists reported finding jugs that had been used for storing wine from 6000 B.C. Wine was used in ceremonies by the Egyptians, traded by the Phoenicians and honored by the Greek god Dionysus and the Roman god Bacchus. By 2014, humanity was consuming more than 6 billion gallons of wine every year.
So why is wine so popular? Aside from its flavors and capacity to help people relax, wine has gained something of a reputation as a "healthy" alcohol — with researchers noting associations between red wine drinking in France and lower incidence of heart disease.
However, wine drinking is also known to increase risks of serious health issues, including liver cirrhosis, sudden cardiac death, alcoholic cardiomyopathies and cardiac rhythm disorders. Excessive consumption and chronic misuse of alcohol are risk factors contributing to an increase in disease worldwide.
How does the average drinker know what to believe? And how much wine is safe? As medical researchers, we recently published an in-depth analysis of the anatomy of wine. This included analysis of the risks and benefits of consumption, comparisons with other alcoholic beverages and a discussion about wine's much-publicized health benefits.
Modern scientific intrigue surrounding wine has grown immensely since the 1970s, when large, international studies first reported a link between light to moderate consumption of alcohol and lower rates of ischemic heart disease (IHD) occurrence and associated deaths. IHDs are a group of diseases characterized by a reduced blood flow to the heart, and they account for significant deaths worldwide.
Similar results have been reported individually for wine, specifically red wine. This phenomenon was eventually coined "the French paradox" after two scientists, Serge Renaud and Michel de Lorgil, observed a relatively low risk of IHD-associated mortality in red-wine drinkers despite a consumption of a diet rich in saturated fat (such as that found in some French food).
Does this mean red wine is good for the heart? This is a complex question, and as yet there is no consensus on the answer. More than one factor needs to be considered to explain this situation. Drinking patterns, lifestyle characteristics and dietary intake are all important for individuals to obtain a healthy cardiovascular profile.
The Mediterranean diet has been put forward as one explanation. This diet emphasizes consumption of plant-based foods in addition to the moderate consumption of red wine and has been labeled as beneficial by scientific advisory committees.
In the Mediterranean diet, the low consumption of saturated fat, emphasis on a healthy lifestyle and, more independently, alpha-linoleic acid (an essential fatty acid) and red wine, may allow this diet to confer the much researched cardio-protective benefits.
Red wine contains more than 500 chemical substances. One class, called polyphenols, has been widely investigated for imparting the apparent antioxidant and anti-inflammatory effects of red wine.
Alcohol and polyphenols are thought to have several positive health impacts. One is a contribution to an increase in HDL cholesterol, or "good cholesterol," and a decrease in LDL oxidation, or "bad cholesterol." They also contribute to a decrease in inflammation. They are thought to increase insulin sensitivity and improve blood pressure.
There is no consistent pattern when wine is compared to beer and spirits. Some report wine's superiority in reducing the risk of IHD and mortality. Others report it for beer and spirits. Others suggest there is no difference. This suggests that alcohol and polyphenols both contribute to explaining the French paradox, in addition to lifestyle factors.
Despite the beneficial effects of wine and alcohol consumption, drinking is still a potential risk factor for atrial fibrillation, the most common "rhythm alteration" of the heart.
In much of the research, adverse effects were increasingly observed with excessive or binge consumption of wine, while low to moderate intakes lowered IHD and mortality risks.
In response, various governing bodies have come forth with guidelines for alcohol consumption. These follow similar patterns but vary remarkably by country and source. And the definition of "one standard drink" used in each guideline is highly variable and discrepant between country borders. This causes great confusion. Readers should be wary of this when interpreting alcohol consumption guidelines.
The World Health Organization recommends low-risk alcohol consumption of no more than two standard drinks per day with at least two non-drinking days during the week. Here, one standard drink is defined as 10 grams of pure ethanol.
The American Heart Association recommends alcohol in moderation — less than or equal to one to two drinks per day for men and one drink per day for women. Here, one drink is defined as 12 ounces of beer, four ounces of wine, 1.5 ounces of 80-proof spirits or one ounce of 100-proof spirits.
The Dietary Guidelines for Americans 2015-2020 developed by the U.S. Department of Agriculture recommends a moderate consumption of alcohol. This equates to up to two standard drinks per day for men and one for women. Here, one standard drink is defined as 14 grams of pure ethanol.
The Canadian Center for Addiction and Mental Health guidelines recommend low-risk alcohol consumption: up to three drinks per day for men and two for women. One drink is defined as 12 ounces of 5 percent beer, five ounces of 12 percent wine and 1.5 ounces of 40 percent spirits.
Observational data around alcohol consumption and heart health suggests that a light to moderate intake, in regular amounts, appears to be healthy. However, when mathematical models have been applied to determine causation (an approach known as Mendelian randomization), the results have been mixed.
Some studies have found light to moderate drinking beneficial, while others have reported long-term alcohol consumption to be harmful for the heart.
For doctors, it is quite clear what to recommend to patients when it comes to diet, exercise and smoking. Given the inconsistencies in the findings relating to alcohol, and wine specifically, recommendations for consumption are less obvious.
For wine drinkers, too, definitive answers on wine and health remain elusive. There is, however, immense research potential in this area for the future.
And as all the guidelines say, one or two glasses of red wine at the end of a long week should be just fine.
Baranchuk is a professor of medicine at Queens University in Ontario. Alexander is a medical student there, and Haseeb is an undergraduate student. This article was originally published on theconversation.com.