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For years, Canadians have been told drinking alcohol in moderation is safe and even beneficial to their health. But a new large-scale study provides more evidence that the healthiest amount of alcohol consumption may be none at all.

Researchers of the study, published in the CMAJ on Monday, analyzed survey data from nearly 10,400 participants in Hong Kong and more than 31,000 participants in the United States. They found men and women lifetime abstainers of alcohol reported the highest level of mental well-being at the start of the study, and women who drank moderately saw an improvement in their mental well-being after they quit.

“Our study provides more evidence suggesting caution in recommending moderate drinking as part of a healthy diet,” co-author Michael Ni, a clinical assistant professor in the school of public health at the University of Hong Kong, wrote in an e-mail. “Quitting drinking even at moderate levels was shown to be linked to a favourable change in mental well-being in both Chinese and Americans.”

The study adds to emerging research that challenges the idea that drinking in small doses is good for one’s health. These findings come at a time when health experts, including Canada’s chief public health officer Theresa Tam, have voiced concerns over high rates of alcohol consumption among Canadians. In her 2018 report on the state of public health in Canada, released last fall, Dr. Tam said Canadians are not paying enough attention to the harms of alcohol. She noted nearly 80 per cent of Canadians, ages 15 and older, had reported drinking alcohol in the past year.

The researchers examined the drinking patterns of adult participants and the changes in their physical and mental well-being between 2009 and 2013 in the Hong Kong cohort, and between 2001 and 2005 in the U.S. cohort.

The study did not include people who were heavy drinkers. Moderate drinkers were considered those who had an average of 14 drinks (196 g of alcohol) or fewer a week for men, and seven drinks (98 g) or fewer a week for women.

Among both the Hong Kong and U.S. samples, women who quit drinking were found to have greater improvements to their mental well-being compared with lifetime abstainers, but the same pattern was not found in men.

While the researchers said the reasons for these improvements are still unclear, they suggested the neurotoxic effects of alcohol may reverse after quitting. Alcohol cessation may also reduce stress in the form of family conflicts or work and legal troubles, they said. It may also be possible that some women received a psychological boost from successfully giving up alcohol.

Although the study involved Hong Kong and U.S. citizens, its findings are relevant to Canadians, said Canadian Medical Association Journal senior editor Ken Flegel.

While there are some differences in the way alcohol is metabolized between cultural groups, “they aren’t major,” Dr. Flegel said. “And the bad effects of alcohol seem to be universal.”

At the Canadian Centre on Substance Use and Addiction, senior research and policy analyst Catherine Paradis, who was not involved in the study, said the mantra of ″one drink a day keeps the doctor away" has persisted for around 20 years. This message has been based on studies suggesting low doses of alcohol reduce people’s risk of developing cardiovascular disease.

But lately, she said, better-designed studies cast doubt about the health benefits of alcohol.

“Now we know that that’s not really the fact," Dr. Paradis said. "More and more, we doubt this idea that there’s this protective effect of drinking.”

Dr. Paradis added that given the harms associated with drinking, she worries about efforts to liberalize alcohol sales in Canada. Well-recognized measures to lower overall population-level alcohol consumption include reducing the availability of alcohol, such as restricting sales to retail monopolies, reducing its affordability through taxation and restricting alcohol advertising and marketing, she said.

“What is concerning right now is we are going in the complete opposite direction in this country,” she said. “We need to rethink this. If not, we will wake up with a national hangover in a few years.”

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