"Seven alcoholic drinks a week can help to prevent heart disease," the Daily Mirror reports. A US study suggests alcohol consumption up to this level may have a protective effect against heart failure…
"Seven alcoholic drinks a week can help to prevent heart disease," the Daily Mirror reports. A US study suggests alcohol consumption up to this level may have a protective effect against heart failure.
This large US study followed more than 14,000 adults aged 45 and older for 24 years. It found those who drank up to 12 UK units (7 standard US "drinks") per week at the start of the study had a lower risk of developing heart failure than those who never drank alcohol.
The average alcohol consumption in this lower risk group was about 5 UK units a week (around 2.5 low-strength ABV 3.6% pints of lager a week).
At this level of consumption, men were 20% less likely to develop heart failure compared with people who never drank, while for women it was 16%.
The study benefits from its large size and the fact data was collected over a long period of time.
But studying the impact of alcohol on outcomes is fraught with difficulty. These difficulties include people not all having the same idea of what a "drink" or "unit" is.
People may also intentionally misreport their alcohol intake. We also cannot be certain alcohol intake alone is giving rise to the reduction in risk seen.
Steps you can take to help reduce your risk of heart failure – and other types of heart disease – include eating a healthy diet, achieving and maintaining a healthy weight, and quitting smoking (if you smoke).
Where did the story come from?
The study was carried out by researchers from Brigham and Women's Hospital in Boston, and other research centres in the US, the UK and Portugal.
It was published in the peer-reviewed European Heart Journal.
The UK media generally did not translate the measure of "drinks" used in this study into UK units, which people might have found easier to understand.
The standard US "drink" in this study contained 14g of alcohol, and a UK unit is 8g of alcohol. So the group with the reduced risk actually drank up to 12 units a week.
The reporting also makes it seem as though 12 units – what is referred to in the papers as "a glass a day" – is the optimal level, but the study cannot not tell us this.
While consumption in this lower risk group was "up to" 12 units per week, the average consumption was about 5 units per week. This is about 3.5 small glasses (125ml of 12% alcohol by volume) of wine a week, not a "glass a day".
And the poor old Daily Express got itself into a right muddle. At the time of writing, its website is actually running two versions of the story.
One story claims moderate alcohol consumption was linked to reduced heart failure risk, which is accurate.
The other story claims moderate alcohol consumption protects against heart attacks, which is not accurate, as a heart attack is an entirely different condition to heart failure.
What kind of research was this?
This was a large prospective cohort study looking at the relationship between alcohol consumption and the risk of heart failure.
Heavy alcohol consumption is known to increase the risk of heart failure, but the researchers say the effects of moderate alcohol consumption are not clear.
This type of study is the best way to look at the link between alcohol consumption and health outcomes, as it would not be feasible (or arguably ethical) to randomise people to consume different amounts of alcohol over a long period of time.
As with all observational studies, other factors (confounders) may be having an effect on the outcome, and it is difficult to be certain their impact has been entirely removed.
Studying the effects of alcohol intake is notoriously difficult for a range of reasons. Not least is what can be termed the "Del Boy effect": in one episode of the comedy Only Fools and Horses, the lead character tells his GP he is a teetotal fitness fanatic when in fact the opposite is true – people often misrepresent how healthy they are when talking to their doctor.
What did the research involve?
The researchers recruited adults (average age 54 years) who did not have heart failure in 1987 to 1989, and followed them up over about 24 years.
Researchers assessed the participants' alcohol consumption at the start of and during the study, and identified any participants who developed heart failure.
They then compared the likelihood of developing heart failure among people with different levels of alcohol intake.
Participants came from four communities in the US, and were aged 45 to 64 years old at the start of the study. The current analyses only included black or white participants. People with evidence of heart failure at the start of the study were excluded.
The participants had annual telephone calls with researchers, and in-person visits every three years.
At each interview, participants were asked if they currently drank alcohol and, if not, whether they had done so in the past. Those who drank were asked how often they usually drank wine, beer, or spirits (hard liquor).
It was not clear exactly how participants were asked to quantify their drinking, but the researchers used the information collected to determine how many standard drinks each person consumed a week.
A drink in this study was considered to be 14g of alcohol. In the UK, 1 unit is 8g of pure alcohol, so this drink would be 1.75 units in UK terms.
People developing heart failure were identified by looking at hospital records and national death records. This identified those recorded as being hospitalised for, or dying from, heart failure.
For their analyses, the researchers grouped people according to their alcohol consumption at the start of the study, and looked at whether their risk of heart failure differed across the groups.
They repeated their analyses using people's average alcohol consumption over the first nine years of the study.
The researchers took into account potential confounders at the start of the study, including:
- health conditions, including high blood pressure, diabetes, coronary artery disease, stroke and heart attack
- cholesterol levels
- body mass index (BMI)
- physical activity level
- educational level (as an indication of socioeconomic status)
What were the basic results?
Among the participants:
- 42% never drank alcohol
- 19% were former alcohol drinkers who had stopped
- 25% reported drinking up to 7 drinks (up to 12.25 UK units) per week (average consumption in this group was about 3 drinks per week, or 5.25 UK units)
- 8% reported drinking 7 to 14 drinks (12.25 to 24.5 UK units) per week
- 3% reported drinking 14 to 21 drinks (24.5 to 36.75 UK units) per week
- 3% reported drinking 21 drinks or more (36.75 UK units or more) per week
People in the various alcohol consumption categories differed from each other in a variety of ways. For example, heavier drinkers tended to be younger and have lower BMIs, but be more likely to smoke.
Overall, about 17% of participants were hospitalised for, or died from, heart failure during the 24 years of the study.
Men who drank up to 7 drinks per week at the start of the study were 20% less likely to develop heart failure than those who never drank alcohol (hazard ratio [HR] 0.80, 95% confidence interval [CI] 0.68 to 0.94).
Women who drank up to 7 drinks per week at the start of the study were 16% less likely to develop heart failure than those who never drank alcohol (HR 0.84, 95% CI 0.71 to 1.00).
But at the upper level of the confidence interval (1.00), there would be no actual difference in risk reduction.
People who drank 7 drinks a week or more did not differ significantly in their risk of heart failure compared with those who never drank alcohol.
Those who drank the most (21 drinks per week or more for men, and those drinking 14 drinks per week or more for women) were more likely to die from any cause during the study.
How did the researchers interpret the results?
The researchers concluded that, "Alcohol consumption of up to 7 drinks [about 12 UK units] per week at early middle age is associated with lower risk for future HF [heart failure], with a similar but less definite association in women than in men."
This study suggests drinking up to about 12 UK units a week is associated with a lower risk of heart failure in men compared with never drinking alcohol.
There was a similar result for women, but the results were not as robust and did not rule out the possibility of there being no difference.
The study benefits from its large size (more than 14,000 people) and the fact it collected its data prospectively over a long period of time.
However, studying the impact of alcohol on outcomes is fraught with difficulty. These difficulties include people not being entirely sure what a "drink" or a "unit" is, and reporting their intakes incorrectly as a result.
In addition, people may intentionally misreport their alcohol intake – for example, if they are concerned about what the researchers will think about their intake.
Also, people who do not drink may do so for reasons linked to their health, so may have a greater risk of being unhealthy.
Other limitations are that while the researchers did try to take a number of confounders into account, unmeasured factors could still be having an effect, such as diet.
For example, these confounders were only assessed at the start of the study, and people may have changed over the study period (such as taking up smoking).
The study only identified people who were hospitalised for, or died from, heart failure. This misses people who had not yet been hospitalised or died from the condition.
The results also may not apply to younger people, and the researchers could not look at specific patterns of drinking, such as binge drinking.
Although no level of alcohol intake was associated with an increased risk of heart failure in this study, the authors note few people drank very heavily in their sample. Excessive alcohol consumption is known to lead to heart damage.
The study also did not look at the incidence of other alcohol-related illnesses, such as liver disease. Deaths from liver disease in the UK have increased 400% since 1970, due in part to increased alcohol consumption, as we discussed in November 2014.
The NHS recommends that:
- men should not regularly drink more than 3-4 units of alcohol a day
- women should not regularly drink more than 2-3 units a day
- if you've had a heavy drinking session, avoid alcohol for 48 hours
Here, "regularly" means drinking this amount every day or most days of the week.
The amount of alcohol consumed in the study group with the reduced risk was within the UK's recommended maximum consumption limits.
But it is generally not recommended that people take up drinking alcohol just for any potential heart benefits. If you do drink alcohol, you should stick within the recommended limits.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.