"Just one alcoholic drink a day could shorten your life," reports BBC News.
A huge study of almost 600,000 drinkers showed that people who drank more than 12.5 units (100g) of alcohol a week were likely to die sooner than those who drank no more than this amount. The results applied equally to women and men.
The current UK guidelines advise limiting alcohol intake to 14 units a week for women and men. This is equivalent to drinking no more than 6 pints of average-strength beer (4% ABV) or 7 medium-sized glasses of wine (175ml, 12% ABV) a week.
These limits are lower than the levels for many other countries, but this latest study suggests they are about right.
The researchers calculated life would be shortened by an average of 1.3 years for women and 1.6 years for men for people aged 40 who drank above the UK weekly limit in comparison with those drinking below the limit.
The study also looked at the likelihood of having a range of non-fatal, but potentially life-changing, cardiovascular conditions, including heart attacks, heart failure and stroke.
Drinking more alcohol was linked to higher chances of all cardiovascular conditions except heart attacks, where it was linked to a lower chance. However, greater risks from other causes of death outweighed any advantage that might bring.
This high-quality study provides further evidence to support the current UK guidelines advising people to drink no more than 14 units a week. Find out more about calculating units of alcohol.
Where did the story come from?
The study was carried out by a collaboration of 120 researchers worldwide, from regions including Australia, Europe, Japan, the UK and the US. It was funded by the UK Medical Research Council, British Heart Foundation, National Institute for Health Research in the UK, European Union and European Research Council.
It was published in the peer-reviewed medical journal The Lancet on an open-access basis so is free to read online.
The study was covered widely in the UK media, with many outlets reporting variations on the life expectancy that could be lost for every drink or number of drinks consumed.
The Daily Telegraph wrote: "Six glasses of wine a week is too much despite government guidelines suggesting it is a safe limit." While the study did suggest 12.5 units is the threshold above which risks start to rise, the difference in risk between people drinking 12.5 and 14 units was small. There's also no agreed classification for the size of a glass of wine.
As statistics expert Professor David Spiegelhalter explained, the study "estimates that, compared to those who only drink a little, people who drink at the current UK guidelines suffer no overall harm in terms of death rates".
What kind of research was this?
This was a meta-analysis of individual-level data from 83 prospective cohort studies carried out in 19 countries. This type of research – especially when carried out at this scale and with the care the authors took to ensure their methods were robust – is a good way to summarise the best research we have on a particular subject.
However, the studies analysed were all observational studies, as it wouldn't be ethical to carry out studies where some people were encouraged to drink an unhealthy amount of alcohol. This means we have to be cautious when saying alcohol was the direct cause of the additional deaths, because other confounding factors may have affected the results.
What did the research involve?
Researchers gathered data from 83 studies, starting between 1964 and 2010, that had information about drinkers who didn't have cardiovascular disease at the start of the study, their level of alcohol consumption and additional health data, and that followed up the participants.
After making adjustments for potential factors that might affect the results – such as age, sex, smoking and physical exercise – they carried out statistical analyses to calculate how different levels of alcohol consumption affected people's risk of:
The researchers used a big dataset of life expectancy models to calculate how the relative risks of drinking different amounts of alcohol would affect the life expectancy of people aged 40.
What were the basic results?
Of the 599,912 people in the study, 40,310 died and 39,018 got cardiovascular disease during an average 7.5 years of follow-up. About half of the people in the study reported drinking more than 12.5 units of alcohol a week.
Looking at different levels of alcohol consumption, the researchers found:
- people drinking up to 12.5 units of alcohol a week had the lowest risk of death from any cause
- above that level, the risk of death rose to a more than 30% increased risk for those drinking more than 37 units a week
- each additional 12.5 units of alcohol consumed each week increased the risk of stroke by 14% (hazard ratio [HR] 1.14, 95% confidence interval [CI] 1.10 to 1.17)
- each additional 12.5 units of alcohol consumed each week decreased the risk of heart attack by 6% (HR 0.94, 95% CI 0.91 to 0.97)
- the risk of all other cardiovascular conditions increased with each additional 12.5 units of alcohol consumed
When they applied their figures to life expectancy at age 40, the researchers calculated that compared with people drinking up to 12.5 units a week:
- those who drank 12.5 to 25 units a week were likely to live 6 months less
- those who drank 25 to 44 units were likely to live 1 to 2 years less
- those who drank more than 44 units were likely to live 4 to 5 years less
Looking at UK limits (14 units a week), the researchers said that compared with those who drank within current limits:
- men who drank above the limits would lose an average of 1.6 years (95% CI 1.3 to 1.8)
- women who drank above the limit would lose an average of 1.3 years (95% CI 1.1 to 1.5)
How did the researchers interpret the results?
The researchers said their main finding was that the lowest risk for avoiding harm from alcohol was found in people drinking no more than 100g, or 12.5 units, of alcohol a week.
They said their detailed analysis of cardiovascular conditions helped to explain the complex links between drinking alcohol and cardiovascular disease, which increased risk of conditions mainly caused by high blood pressure but slightly decreased risks of heart attacks – possibly because of links between alcohol and cholesterol.
They concluded: "These data support adoption of lower limits of alcohol consumption than are recommended in most current guidelines."
This was an impressive study that analysed a lot of high-quality data. It offers strong evidence to support recommendations that people drink within relatively low alcohol limits, like those recently introduced in the UK.
The work regarding cardiovascular disease and heart attacks is useful and challenges the widespread belief that alcohol reduces the risk of cardiovascular conditions. While that may be true for heart attacks, it's isn't for stroke or other conditions.
The study did have a couple of limitations that are worth noting.
In many of the individual studies included in the meta-analysis, the participants were asked only once about how much alcohol they drank – and people are notoriously bad at accurately reporting their drinking. However, if people in the studies routinely underestimated their alcohol consumption, that would mean the meta-analysis results tend towards underestimating the harm alcohol causes.
And while the researchers did their best to account for a range of factors that could have affected the results, it's always hard to control for those completely.
Overall, the study adds weight to the recommendations that both women and men drink within the UK limits of 14 units of alcohol a week.