A lot of well-designed studies have found associations between moderate alcohol consumption and better health. Following large groups of people over time appears to show that those who imbibe about four to seven units – the range fluctuates across research – per week may live longer due to a lower likelihood of stroke and heart attacks and have a lower risk of developing cardiovascular disease, dementia, and diabetes.

Yet other research, like a massive review of nearly 600,000 drinkers from 19 high-income countries that was recently published in The Lancet, has yielded contradictory correlations with cardiovascular conditions, and many have established troubling links between even low levels of consumption and increased prevalence of several types of cancer.

As with any observational study on lifestyle, investigations into the benefits (or lack thereof) of modest boozing are limited by the inability of scientists to fully separate out the effects of other factors. One of the most significant hurdles is comparing drinkers to non-drinkers due to a phenomenon known as the “sick quitter”, wherein people who abstain from alcohol are doing so due to underlying health issues, so those who drink moderately seem to have better health outcomes. (The evidence on high levels of alcohol consumption are unequivocally negative.)

Hoping to finally shed some light on this perplexing issue, the US National Institutes of Health (NIH) supported and helped fund a randomized control trial – the only type of study that can show causation vs correlation – called the Moderate Alcohol and Cardiovascular Health Trial (MACH15).

MACH15 was slated to enroll 7,800 adults 50 years and older, from multiple continents, who were all at similarly high risk for cardiovascular disease and assign them to either drink roughly 15 g of ethanol – equivalent to one 5-oz glass of wine, one 12-oz beer, or one 1.5-oz shot of spirits – per day for six years, or to not touch a drop of alcohol for six years. At the endpoint, the rates of developing cardiovascular disease were going to be compared, thus confirming or refuting the theorized protective effect of alcohol.

But this March, an investigative report in The New York Times revealed the shocking truth about MACH15: the NIH officials and scientists behind the trial had courted major players in the alcohol industry, asking executives at companies such as Anheuser Busch and Heineken to contribute towards the study’s $100 million tab with the assurance that the results would likely support the healthiness of moderate drinking. Due to the deeply permeating impact of both conscious and unconscious bias, researchers are supposed to conduct investigations with neutral expectations, yet the MACH15 team was the opposite of neutral.

This explosive revelation shamed the NIH and forced them to halt enrollment in May so that an internal review could be performed. The federal agency terminated MACH15 on June 15, citing these worrying conflicts of interest and newly discovered problems in the study design that would have helped mask negative consequences of alcohol, including a short follow-up time and exclusion criteria that would weed out women predisposed for breast cancer.

“The National Institutes of Health plans to end funding to the Moderate Alcohol and Cardiovascular Health (MACH) trial. The decision is based on concerns about the study design that cast doubt on its ultimate credibility,” said the NIH announcement. “This includes whether the study would effectively address other significant consequences of moderate alcohol intake, such as cancer.

Moving forward, it may be a while until a new randomized control trial on moderate alcohol is initiated. But some researchers don’t see this as so great a loss.

As University of Minnesota social epidemiologist Toben Nelson explained to The Washington Post, people who don’t drink don’t need science to give them a reason to start. What’s truly important is convincing heavy drinkers to drink less.

[H/T: The Washington Post and The New York Times]