Alcohol, heart health, and the puzzle for scientists

A quick Google search on the topic throws up hundreds of papers with seemingly contradictory or counterintuitive findings, yet the World Health Organisation (WHO) warns that there is "no safe amount".

The debate was reignited this week by a new study widely interpreted as showing that consuming one alcoholic drink per day for women and between one and two for men actually reduces the risk of cardiovascular disease.

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The study, led by investigators at Massachusetts general hospital in the US, had set out to unravel the potential mechanisms behind a phenomenon previously observed by some other researchers - namely that light-to-moderate drinkers appear to have lower rates of heart problems than non-drinkers.

This particular finding was illustrated most clearly in a BMJ paper published in March 2017 by a group of epidemiologists and public health experts from Cambridge University and University College London.

The BMJ study - the most comprehensive ever undertaken - had tracked alcohol intake and health outcomes among nearly two million adults in England aged 30 or older over who had no prior history of cardiovascular disease.

People in Scotland continue to consume more alcohol per head than other parts of the UK, with deaths on the rise (Image: PA)

GP records, hospital admissions and mortality were compared over a 13-year span, from 1997 to 2010.

Nearly 115,000 of the participants had gone on to suffer a cardiovascular diagnosis during the follow-up period.

When the researchers drilled down into the statistics they discovered that non-drinkers had higher rates of heart attacks, heart failure, ischaemic stroke, unstable angina, and abdominal aortic aneurysms than the light-to-moderate drinkers, even after adjusting for differences in age, sex, socioeconomic deprivation, smoking status, diabetes, cholesterol or blood pressure.

Haemorrhagic stroke was the only exception.

They described it as a "classic J-shaped association for cardiovascular disease (all and fatal) and all cause mortality, with non-drinkers, former drinkers, and heavy drinkers having an increased risk compared with moderate drinkers".

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There were some limitations to the study, however, which the researchers acknowledged.

For example, they noted that intake was based on self-reported estimates and people are known to downplay or misremember alcohol consumption.

As a result "some of the occasional drinkers were probably regular/moderate drinkers while some moderate drinkers were likely to be heavy drinkers".

They were also "unable to account for differences in risk by beverage type".

There is a widespread belief that the antioxidants found in red wine may help to prevent coronary heart disease when consumed in moderation, but in reality this is difficult to untangle from other confounding factors.

For example, red wine drinkers tend to be better educated and more affluent which in turn is associated with access to better quality food, healthier diets, and more active lifestyles.

The alcohol-specific death rate is on the rise in Scotland, especially among males, but it is harder to gauge the impact of alcohol on overall mortality from cancer to cardiovascular causes as well as violence and accidents (Image: NRS)

The researchers behind the 2017 study acknowledge that they were unable to adjust for factors such dietary habits or levels of exercise as this information was not included in the electronic database where participants' details were logged.

Nor were they able to adjust for levels of tobacco exposure among smokers (how many cigarettes per day, number of years as a smoker etc) or for differences in drinking patterns, which is significant given that "even isolated episodes of heavy drinking [ie. binge drinking] are enough to eliminate the protective effects observed for coronary heart disease in otherwise moderate drinkers".

One of the problems of evaluating the interplay between lifestyle factors and health is that they are by necessity observational, which makes it impossible to control for every possible variable.

The research published this week, however, pointed to another possible mechanism which might explain why light to moderate drinkers are at lower risk of certain cardiovascular events (if indeed they really are).

Red wine is often touted as a form of alcohol with benefits for the heart, but it is difficult to unpick from other lifestyle factors (Image: Getty)

READ MORE: Scots still drinking too much as drop in alcohol intake stalls 

The study, published in the Journal of the American College of Cardiology, suggests that reduced stress may be the key.

They note that chronic stress is associated with major adverse cardiovascular events (MACE), while light-to-moderate alcohol consumption "has been linked to lower MACE risk" for reasons that are "unclear".

When they examined patient data for more than 53,000 people whose details were stored in the Mass General Brigham Biobank, a research database created by Massachusetts general hospital (MGH), they found that the light-to-moderate drinkers did indeed appear to have a lower risk of MACE compared to people who consumed minimal to no alcohol.

Brain scans were also examined for a subset of 713 participants.

These revealed that the low-to-moderate drinkers had decreased levels of stress-related neural network activity (SNA) compared to the non-drinkers.

Illustration from the Journal of the American College of Cardiology paper (Image: JACC)

This is not necessarily surprising.

It is known that, during times of stress, the brain's emotional control centre - the amygdala - sends out hormonal panic signals, but that alcohol can dampen down that effect.

As Dr Ahmed Tawakol, the study's author and co-director of the Cardiovascular Imaging Research Centre at MGH, put it: “When the amygdala is too alert and vigilant, the sympathetic nervous system is heightened, which drives up blood pressure and increases heart rate, and triggers the release of inflammatory cells.

“If the stress is chronic, the result is hypertension, increased inflammation, and a substantial risk of obesity, diabetes, and cardiovascular disease.”

What really struck the researchers, however, was that the light-to-moderate drinkers appeared to experience an ongoing dampening of activity in the amygdala which was associated with a 22% reduction in cardiovascular disease.

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The effect was even more pronounced - 40% - when the analysis was narrowed to participants with a medical history of anxiety, a condition characterised by an overactive stress network.

The problem is that heart health is only part of the equation.

Within Europe for example, it is estimated that half of all alcohol-attributable cancers - and the majority of breast cancers - are caused by "light" to "moderate" drinking (less than one bottle of wine per week).

A safer way to achieve the same amygdala effect is through good quality sleep or exercise, although efforts are also underway to recreate it pharmacologically.

Think of it as a small glass of wine in pill form.