What happens when one twin drinks more than the other twin? Does the one who drinks more have a higher or lower risk of heart disease?

Alcohol doesn’t prevent heart disease

Numerous studies show that people who drink moderate amounts of alcohol have the lowest risk of heart disease. But according to a new study on Norwegian twins, alcohol is not the protective factor.

Alcohol is going through hard times at the moment.

More and more research suggests that even low alcohol consumption might increase the risk of several types of cancer. One study published in The Lancet Oncology last year found that around 740 000 cases of cancer were attributable to alcohol consumption.

But what about heart disease? A large number of studies have shown that people who drink moderate amounts of alcohol have a lower risk of cardiovascular disease than those who abstain.

Does alcohol protect the heart from disease?

Well, it turns out that question does not have an easy answer. Studies have shown that alcohol is not the only factor that separates people who drink from those who don’t.

Eivind Ystrøm is a professor at the University of Oslo and the Norwegian Institute of Public Health.

For example, people who consume moderate amounts of alcohol often have a higher education level than those who drink less. They tend to come from families with higher social and economic status.

Maybe they're smarter, even.

A previous study has shown that people with a high IQ at the age of 18 more often drank more in their 40s than individuals with a lower IQ.

Natural experiments

Maybe it's not the alcohol but another lifestyle factor that protects against cardiovascular disease.

This question has not been easy to figure out.

Running 50-year-long trials – where some people are given cases of beer and wine and told to drink every day, while others are directed to abstain – is impossible for ethical and practical reasons.

Nevertheless, there are ways to get more conclusive answers, says Eivind Ystrøm, a professor at the Department of Psychology, University of Oslo (UiO), and a senior researcher at the Norwegian Institute of Public Health.

“Using natural experiments is one such method,” he says.

These are situations that are similar to what would be done in a study, but that occur naturally. In this case, the experiment involves identical twins.

Twin study

“Identical twins have the same genes, and they’ve grown up in the same family environment. This means you can eliminate the effect of the family,” Ystrøm says.

In other words: The researchers can compare sets of twins where the two siblings have different levels of alcohol consumption. Does this result in differences in their risk of dying from cardiovascular disease? If so, this difference cannot be explained by inheritance or environment in their growing up, but probably has something to do with the drinking itself.

Ystrøm and his colleagues from UiO and the Norwegian Institute of Public Health have used this method for their experiment.

The researchers compared data from the Norwegian Twin Registry and the Norwegian Cause of Death Registry for over 14 000 Norwegian twins born between 1915 and 1960.

The participants in the twin registry had provided information about lifestyle, including alcohol consumption, on two occasions during their lives. During the follow-up period, more than 3600 of the participants had died. Approximately 1200 had died of cardiovascular disease.

This made it possible to see if there was any connection between drinking and the cause of death.

Flipped from lower to higher risk

When the researchers examined the individual risk of dying from heart disease, a well-known pattern emerged.

“Individuals who came from a family that drank quite a lot, had an almost 50 per cent lower risk of dying from cardiovascular disease, as compared to people from families who drank less,” says Ystrøm.

Something in these families was thus providing strong protection against heart disease.

But when the researchers compared both twins in the twin pairs with each other, the picture changed.

In many cases, one of the twins drank significantly more than the other.

“Then we saw that the twin who drank a lot had more than a 30 per cent higher risk of dying from cardiovascular disease than the twin who drank less," Ystrøm says.

Ystrøm believes that there must be some underlying factor in these families that protects against heart disease, but at the same time increases the tendency to drink a lot. The researcher believes this protective effect probably hides the negative effect of alcohol.

But what exactly is the protective element?

Related to education

Ystrøm admits that it's a bit of a mystery, but he has a few thoughts about what might be going on.

“We’re seeing that the genetic factors that increase the risk of drinking often and a lot, are related to higher education and intelligence. These aren’t the same genes as the ones that carry the risk of destructive drinking, mental illness and drug addiction,” he says.

Could there be something about having an academic bent that also makes you like the effect of alcohol?

Education and intelligence might lead to healthier choices on other fronts, such as healthier foods or less smoking.

Higher education typically offers a profession with less strain and shift work, which can affect your health. The connection could also involve these families having more money and resources.

Valuable addition to research

What do these results tell us regarding our knowledge of alcohol and health?

“The results are a valuable addition to the literature on alcohol and cardiovascular disease,” writes Per Magnus, who is a department director at the Norwegian Institute of Public Health.

“They show that the connection between alcohol consumption and heart disease disappears once you adjust for shared genetic and environmental factors in families.”

Magnus believes that the study has some weaknesses.

“Other non-genetic factors that could cause one identical twin to drink more alcohol have not been taken into account,” he says.

A lot of possible reasons could exist as to why one twin drinks more, such as different social and work circles or traumatic accidental events. The question then becomes whether these factors in and of themselves might also affect the risk of heart disease.

No increased risk of other diseases

Interestingly, higher alcohol consumption did not affect other causes of death than heart disease, such as cancer. Although many of the twins died of other diseases, this did not seem to be related to how much they drank.

Nor was it the case that twins who drank a lot had a greater risk of dying during the study period. This must mean that individuals who drank a lot had slightly fewer deaths from other causes.

However, Ystrøm believes that alcohol is unlikely to have any protective effect. Other statistical connections, such as competing risk, are more likely.

“Sometimes you can get paradoxical findings. For example, previous studies have found that smoking seemed to protect against Alzheimer's. But the reason was simply that the smokers died of other diseases before they had time to get Alzheimer's,” says Ystrøm.

Doesn’t believe in prohibition

So, should we be aiming to abstain from all use of alcoholic beverages in light of these and other findings on alcohol and health?

“Numerous other studies indicate that frequent alcohol consumption is associated with an increased risk of a number of injuries and diseases,” Magnus writes from FHI.

However, he refrains from saying that because of medical reasons people shouldn’t indulge in an occasional drink.

“Each individual has to do their own cost-benefit analysis based on the pleasure of using alcohol versus its disadvantages,” he writes.

Ystrøm does not believe that banning alcohol is a good idea.

“That’s been tried before, with unfortunate consequences. But maintaining Vinmonopolet, Norway’s state-owned alcohol retailer, and a restrictive policy with low availability and high prices could add many years of life,” he says.

“People also need to know that there’s a link. Alcohol is addictive, and you can end up in a lifestyle where you drink a lot multiple days a week.”

Ystrøm thinks we can probably enjoy life just as much even if we cut our consumption a little.

“The third glass doesn’t necessarily add that much extra enjoyment,” he says.

Translated by: Ingrid P. Nuse


Eivind Ystrom et.al.: Alcohol consumption and lower risk of cardiovascular and all-cause mortality: the impact of accounting for familial factors in twins. Psychological Medicine, 2022.

The study is supported by the Research Council of Norway and is a collaboration between the Department of Mental Disorders at the Norwegian Institute of Public Health, the Department of Community Medicine and Global Health at UiO, the Department of Clinical Medicine at the University of Tromsø and the PROMENTA Research Centre at UiO.

What constitutes moderate alcohol consumption?

Moderate alcohol consumption in Norway is defined as drinking between six and 12 units per week. One unit is equivalent to a small bottle of beer or a small glass of wine.


Read the Norwegian version of this article at forskning.no

Powered by Labrador CMS