Consuming alcohol - Even amounts of it, can have health consequences, found a recent US-based study.
The research published in the Journal of the American Medical Association in November last year comes after years of confusing and sometimes contradictory studies that state too much alcohol is bad but a little bit is good; or that some types of alcohol are better than others. However, the research has found that any amount of alcohol is detrimental to heal - risks from drinking can come from moderate consumption as well.
According to an article in the New York Times, alcohol consumption leads to chronic conditions such as liver disease, cancer and heart disease. Alcohol is also linked to an abnormal heart rhythm, known as atrial fibrillation, which raises the risk of blood clots and stroke.
There is also emerging evidence that there are risks even within permitted alcohol consumption limits - especially for certain types of cancer and some forms of cardiovascular disease, said one of the authors of the study, Marissa Esser, who leads the alcohol programme at the US Centers for Disease Control and Prevention.
According to scientists, the main way alcohol causes health problems is by damaging DNA. When someone drinks alcohol, their body metabolises it into acetaldehyde, a chemical that is toxic to cells.
"Acetaldehyde both damages your DNA and prevents your body from repairing the damage. Once your DNA is damaged, then a cell can grow out of control and create a cancer tumor," Dr Esser explained.
Genes play a role in it as well. Two genetic variants, both of which are more common in people of Asian descent, affect how alcohol and acetaldehyde are metabolised. One gene variant causes alcohol to break down into acetaldehyde faster, flooding the body with the toxin. The other variant slows down acetaldehyde metabolism, meaning the chemical hangs around in the body longer, prolonging the damage.
The risk of developing alcoholic liver disease is greatest in heavy drinkers. However, a report in the US National Library of Medicine stated that five years of drinking just two alcoholic beverages a day can damage the liver. 90%of people who have four drinks a day show signs of alcoholic fatty liver.
Alcohol is a potent carcinogen – it is known to be a direct cause of seven different cancers: head and neck cancers, esophageal cancer, liver cancer, breast cancer and colorectal cancer.
Research suggests there may be a link between alcohol and other cancers as well, including prostate and pancreatic cancer, although the evidence is less clear-cut.
For some cancers, such as liver and colorectal, the risk starts only when people drink excessively. But for breast and esophageal cancer, the risk increases, albeit slightly, with any alcohol consumption. The risks go up the more a person drinks.
"If somebody drinks less, they are at a lower risk compared to that person who is a heavy drinker. Even two drinks per day, one drink per day, may be associated with a small risk of cancer compared to non-drinkers," said Dr Farhad Islami, a senior scientific director at the American Cancer Society.
Pre-existing conditions could also interact with alcohol to affect one's health.
Alcohol also creates oxidative stress, another form of DNA damage that can be particularly harmful to the cells that line blood vessels. Oxidative stress can lead to stiffened arteries, resulting in higher blood pressure and coronary artery disease.
"It fundamentally affects DNA, and that's why it affects so many organ systems. Over the course of a lifetime, chronic consumption damages tissues over time," said Dr Tim Naimi, director of the University of Victoria's Canadian Institute for Substance Use Research.
Some previous studies have claimed that small amounts of alcohol, particularly red wine, can be beneficial. Past research suggested that alcohol raises HDL, the "good" cholesterol, and that resveratrol, an antioxidant found in grapes and red wine, has heart-protective properties.
However, said Mariann Piano, a professor of nursing at Vanderbilt University, "There is been a lot of recent evidence that has really challenged the notion of any kind of what we call a cardio-protective or healthy effect of alcohol."
"The idea that a low dose of alcohol was heart healthy likely arose from the fact that people who drink small amounts tend to have other healthy habits, such as exercising, eating plenty of fruits and vegetables and not smoking. In observational studies, the heart benefits of those behaviors might have been erroneously attributed to alcohol," Dr Piano said.
More recent research has found that even low levels of drinking slightly increase the risk of high blood pressure and heart disease, and the risk goes up dramatically for people who drink excessively.
However, scientists haven't called for abstaining completely, unless one has an alcohol use disorder or is pregnant.
"Alcohol is harmful to the health starting at very low levels. Drink less, live longer. That's basically what it boils down to," Dr Tim Naimi added.