There’s no harm in going to happy hour each day, or enjoying a cold, crisp beer, maybe even a glass of wine when you get home.

Right?

Wrong: Even moderate drinking can be harmful for you, according to a long-term cohort study published Wednesday in the British Medical Journal, refuting conventional wisdom and suggesting that even moderate drinking causes negative brain changes and accelerated cognitive decline.

Tracking the drinking habits and cognitive skills of 550 subjects over 30 years, researchers found that moderate drinkers — people who consumed 14 to 21 units of alcohol a week — “had three times the odds of right sided hippocampal atrophy,” an early marker for Alzheimer’s disease. Heavier drinkers — over 30 units of alcohol a week — were found to be at an even higher risk, while light drinkers — one to under seven units a week — didn’t display any benefits over people who didn’t drink at all. Heavier drinkers also showed a faster decline in lexical fluency, a measure of cognitive performance.

This research comes out of the Whitehall II cohort, a group of 550 British civil servants who have participated in periodical health checkups and questionnaires for 30 years. By following the same large group of people over such a long period of time, researchers have gotten important insights into how certain habits and lifestyles affect people as they age. This particular study topples conventional wisdom, especially in terms of the protective effects of moderate and light drinking.

fMRI moderate alcohol
Researchers found that moderate drinkers exhibited decreased gray matter in the hippocampus, as well as hippocampal atrophy, an early warning sign of Alzheimer's disease.

“We were surprised that light to moderate drinkers didn’t seem to have that protective effect,” study co-author Dr. Anya Topiwala, a psychiatry researcher at the University of Oxford, tells CNN. “These are people who are drinking at levels that many consider social drinkers, so they are not consuming a lot.”

An American unit of alcohol is more than 50 percent larger than its overseas cousin. In other words, the number of drinks that qualify you as a moderate or heavy drinker would be even smaller for U.S. drinkers.

And that’s perhaps why drinkers might not realize they are drinking more than they should. Doctors and scientists have long maintained that moderate drinking is okay — even healthy — protecting against diabetes, ischemic stroke, and heart disease. But what if you’re drinking way more than what makes for “moderate” drinking often?

As a side note, and for the sake of clarity, one “unit of alcohol” means 10 mL of pure alcohol. This translates to the following volumes, according to the U.S. Department of Health: “12 fluid ounces of regular beer (5 percent alcohol), 5 fluid ounces of wine (12 percent alcohol), or 1.5 fluid ounces of 80 proof distilled spirits (40 percent alcohol).”

This study really rocks the boat in terms of the health effects of alcohol. It’s not like the researchers used some bizarro definition of “moderate” alcohol consumption, either. While the U.S Department of Health definition of moderate alcohol consumption is weirdly gender-specific, recommending up to one unit of alcohol per day for women and up to two units a day for men, it’s not too far off from the moderate level of alcohol consumption that this study found to be associated with early warning signs of Alzheimer’s.

So, for those of you who hit the bar after work every day, think twice, at least for your brain.

Abstract: To investigate whether moderate alcohol consumption has a favourable or adverse association or no association with brain structure and function. Observational cohort study with weekly alcohol intake and cognitive performance measured repeatedly over 30 years (1985-2015). Multimodal magnetic resonance imaging (MRI) was performed at study endpoint (2012-15). 550 men and women with mean age 43.0 (SD 5.4) at study baseline, none were “alcohol dependent” according to the CAGE screening questionnaire, and all safe to undergo MRI of the brain at follow-up. Twenty three were excluded because of incomplete or poor quality imaging data or gross structural abnormality (such as a brain cyst) or incomplete alcohol use, sociodemographic, health, or cognitive data. Structural brain measures included hippocampal atrophy, grey matter density, and white matter microstructure. Functional measures included cognitive decline over the study and cross sectional cognitive performance at the time of scanning. Higher alcohol consumption over the 30 year follow-up was associated with increased odds of hippocampal atrophy in a dose dependent fashion. While those consuming over 30 units a week were at the highest risk compared with abstainers (odds ratio 5.8, 95% confidence interval 1.8 to 18.6; P≤0.001), even those drinking moderately (14-21 units/week) had three times the odds of right sided hippocampal atrophy (3.4, 1.4 to 8.1; P=0.007). There was no protective effect of light drinking (1-<7 units/week) over abstinence. Higher alcohol use was also associated with differences in corpus callosum microstructure and faster decline in lexical fluency. No association was found with cross sectional cognitive performance or longitudinal changes in semantic fluency or word recall. Alcohol consumption, even at moderate levels, is associated with adverse brain outcomes including hippocampal atrophy. These results support the recent reduction in alcohol guidance in the UK and question the current limits recommended in the US.

Photos via Anya Topiwala et al, Giphy / Comedy Central