There is a difference between fresh fruit juices and those made from concentrate. Image © Public domain, CC0, via Wikimedia Commons.

A study of 27,000 people globally has found that fizzy drinks, fruit juices and fruit drinks, and coffee can markedly increase the chance of stroke in later life. Here ScienceVega talks to the University of Galway’s Professor Andrew Smyth, one of the key researchers behind the findings.

The results of new research from the University of Galway in Ireland and McMaster University in Canada are stark: increased consumption of fizzy drinks, fruit juices and fruit drinks and coffee can increase the risk of stroke in later life.

In particular, frequently drinking fizzy drinks can double the risk of stroke, more than four cups of coffee a day increases the chances of a stroke by a third, whilst drinking water and tea may reduce the risk of suffering a stroke.

ScienceVega spoke to the University of Galway’s Professor Andrew Smyth, one of the scientists involved in the near-global study, INTERSTROKE, on the reasons for, and methodology behind, the research. He also discussed the key findings of the work and what considerations we should all make when deciding on our beverage of choice.

Too much coffee might not be good for you. Image © Edward, CC0, via Wikimedia Commons.

ScienceVega: Can you tell me a little bit more about INTERSTROKE and how you and the University of Galway started to or came to lead it?

AS: INTERSTROKE is a worldwide study that was setup multiple years ago in partnership between the University of Galway (Ireland) and McMaster University in Canada. The lead investigator is Professor Martin O’Donnell, now the Dean of Medicine here in Galway.

Our interest was in getting a better idea of risk factors for stroke and to quantify the level of risk with each item, and how that varied across the world. The reason for that is a lot of previous research focused on one country or one region and the majority of the literature tends to focus on North America or western Europe, often where there is better funded research and there’s more information, which doesn’t represent the whole of the globe.

The idea with INTERSTROKE was to build on a previous study called INTERHEART that looked at risk factors for heart attack and involved a network of doctors and scientists across the world who were particularly interested in cardiovascular disease. Through all those different centres, we recruited around 13,500 people who had had their first ever stroke. They were recruited in hospitals across the world, so that we had people from North America, Europe, South America as well as China, south and southeast Asia, and the Middle East. We also had a limited number of people from Australia and Africa, which meant quite a range of people across the world.

Also, every time a person had a stroke and came into the study, the group in the local hospital then tried to find somebody who didn’t have a stroke but was similar in age and sex, so that we could have a control in the study that came from a similar area. Across the globe there are lots of major healthcare, social or cultural factors that impact health and healthcare. We wanted to make fair comparisons between those who did and did not have a stroke; for example we did not want to directly compare somebody who had a stroke in India aged 45 to a 70-year-old in Canada.

We asked people in the study about ten main cardiovascular risk factors (which include risk factors for stroke), such as hypertension (high blood pressure), smoking, and diabetes. The risk factors for different cardiovascular diseases overlap a lot, although there are subtle differences: high blood pressure is perhaps a more important risk factor for stroke than it probably is for heart attack for instance. As all that information was being collected, we also had the chance to look at a participant’s medical records and asked people about their diet, lifestyle, history, family history and beverage intake: how many cups of coffee or tea or water were they drinking a day, for instance.

We also had to look at the differences between types of coffee, black teas and green teas. For instance in Ireland and the UK, when we talk about ‘black tea’ we mean tea without milk in it, but an English breakfast tea is still a black tea regardless of milk. The main difference in types of tea is in how they are processed (leading to the oxidation they experience). There are also important cultural differences in how and when people drink black tea or herbal tea. Where we didn’t have the capacity was to ask people about the type of coffee; it is important to remember that there are key effects from coffee that differ by the way the beans were made, the brew, whether it was instant, whether there were milk, non-dairy additions, sugars or syrups included, (e.g. drinking instant coffee, americano, flat white, etc.). We did ask a general question about whether they added milk to their tea or their coffee.

When it came to fizzy drinks, fruit juices or fruit drinks, that was part of our dietary assessment which included a lot of questions. We asked people whether they consumed fizzy drinks (including sodas), iced tea (which differs between cultures), or tonic waters (we put sparkling water in the water section). We asked how often they consumed fizzy drinks (once a day, twice a day or more) and asked the same question for fruit juices or fruit drinks. Again, there were challenges. For example with fizzy drinks, we didn’t ask whether it was the full sugar version or if it was the ‘healthier’ zero sugar or diet versions, and we didn’t ask if it was energy drinks. We just didn’t have scope to ask that question in the scale of the study.

When it comes to fruit juices and fruit drinks again, being able to differentiate what a fruit juice is from a fruit drink is something that would have been helpful. If you walk around a supermarket in Ireland or the UK, the majority of fruit juice, even the juice in the refrigerators, is made from a concentrate. It’s not 100% freshly squeezed juice that you might have to go to a deli counter to get, for example. Even just within fruit juice itself, not all fruit juices are the same. From a biological perspective, something that is 100% freshly squeezed fruit juice (with no additives, preservatives or sugars) is likely to have many of the vitamins, minerals and the benefits that you tend to get from eating an actual fruit (although it doesn’t have the fibre or other nutrient content). Whereas if you pick up a carton of orange juice that has quite a long shelf life, that’s a very different thing, and more likely to contain additives, chemicals and other substances to ensure it has longer life on the shelf, is cheaper in production and made from a concentrate. We understand there are important economic factors (including the availability and affordability of different drinks), but the biological effects of those types of fruit drinks are probably different.

Finally, some fruit drinks are labelled as ‘flavoured with fruit’, but they’re probably not containing fresh fruit juice. Similarly, for cordials and squash, there may be some fruit juice, but also sugars and other substances. Being able to tease that out would be very helpful, but it would be easier to do country by country rather than in a standardised way across the world. For example, the availability of cordials and squash is very different between countries. While Ireland and the UK would be similar in that sense, they aren’t easily available in Canada, for example.

The findings:

• Fizzy drinks, including both sugar-sweetened and artificially sweetened such as diet or zero sugar, were linked with a 22% increased chance of stroke, and the risk increased sharply with two or more of these drinks a day;
• The link between fizzy drinks and chance of stroke was greatest in eastern/ central Europe and the Middle East, Africa, and South America;
• The research noted that many products marketed as ‘fruit juice’ are made from concentrates and contain added sugars and preservatives, which may offset the benefits usually linked with fresh fruit, and actually increase stroke risk;
• Fruit juice drinks were linked with a 37% increase in chance of stroke due to bleeding (intracranial haemorrhage). With two of these drinks a day, the risk triples;
• Women show the greatest increased chance of stroke due to bleeding (intracranial haemorrhage) linked to fruit juice/ drinks; and
• Drinking more than seven cups of water a day was linked with a reduced odds of stroke caused by a clot.

Regular consumption of fizzy drinks increases your risk of stroke in later life. And is probably not good for your teeth. Image © www.Pixel.la Free Stock Photos, CC0, via Wikimedia Commons.

ScienceVega: How are you hoping to get this message across to younger people?

AS: The first thing to say with our study is that what we’re looking at is a relative increase in your risk of stroke compared to what your actual risk of stroke is. Typically older people, who are at high risk of stroke, need to be very conscious of their beverage intake and the choices they’re making.

When it comes to younger people and teenagers, ultimately, we are saying that everybody needs to be aware that there are potential harms from these things, although they might not have an impact on them until much further down the line. Most people see having a stroke as something that happens to older people. When it comes to fizzy drinks, perhaps it’s important to think about your lifetime exposure and how that may ultimately lead to risks further down the line.

We are trying to encourage people to make healthier choices. It’s not expected or feasible for every teenager to never consume a fruit juice drink or to never consume a fizzy drink, but we need people to be aware that consuming lots of them over time is likely to be linked with poorer health outcomes, far beyond stroke.

If you’re going to have a cold drink and you want to have something that’s not water, read the labels and choose something that has the least amount of additives, preservatives and chemicals. Be careful with the total amount of sugar that you’re consuming, because that can impact your dental health immediately, and it can impact your diabetes and cardiovascular risk in the not-too-distant future. If you want to have a fizzy drink as a treat, then have a fizzy drink as a treat, but also then try to make other choices at other times. Know that it’s important to keep yourself well-hydrated and healthy from that perspective.

ScienceVega: There are so many different variables and you already have something like 27,000 people involved, so what are the next logical steps?

AS: We focused on getting a clear public health message that might be useful and could be applied on a global scale. We acknowledge there are limitations with our study and limits on how strong our messaging can be. With fizzy drinks, we say that people should avoid them as much as you possibly can and, in particular, you really need to be avoiding them completely if you’ve got additional risk factors or things that increase your overall background risk of stroke. That applies to people currently at high risk of stroke, but also to a lot of younger people as the lifetime cumulative exposure to some of these substances has important potential to do some damage.

When it comes to fruit juices and fruit drinks, it’s a harder call to make, because of the differences in availability and affordability of these drinks within and between villages, communities, towns and countries. Fruit juices or drinks aren’t available everywhere and they may not be affordable to everyone. Ultimately the message we want to get across is to encourage people to make as healthy a choice as they possibly can. For example, picking up a carton of a fruit drink or a can of fizzy drink is probably not the best choice, as both were linked with an increased chance of stroke.

Instead we’re encouraging people in that if they want a cold drink, the safest and probably best cold drink for you is water (assuming the water available is safe to drink).

Water: The healthiest beverage. Image © W.J.Pilsak, CC BY-SA 3.0 http://creativecommons.org/licenses/by-sa/3.0/, via Wikimedia Commons.

ScienceVega: When considering different countries and ethnicities, are you talking primarily of where that person has lived, so a person with Indian heritage born and raised in Ireland, for example, would have a different dietary history compared with an Indian person born and raised in India, rather than their actual ethnicity?

AS: It is probably mostly to do with your geographical location. There are some studies that look at whether it’s your genetic ethnicity versus the environment in which you live – as we believe that it’s a combination of both your genetics and your environment that impact health – called the genotype/ phenotype interaction. A very specific but relevant example is that there are genetic tendencies whereby some genetic ethnicities or races are at a higher risk of metabolic conditions. For example, south and southeast Asia are areas of the world where there are increases in risk of diabetes and the complications of diabetes.

That said, there are some other things that triangulate with culture. For example, immigrant communities (including subsequent generations) often have cultural factors that transfer with them, and are passed down through the generations about food and drink, including what you are given as a child. For example, when I was a child growing up in Ireland, coffee was something that not many people drank, and if they did, it was instant coffee. When you look at Ireland now (similar to the UK), there are coffee shops everywhere.

In this study, we found a strong direct correlation between both geographical region and self-identified ethnicity. In some countries, like India, for example, the vast majority identified their ethnicity as south Asian. Other countries, such as Canada, for example, have a very multi-ethnic diverse population. Overall, we didn’t have enough people of ethnicities that were very different to their geographical region to look into this further.

Ultimately for INTERSTROKE, where we were focused on lifestyle and behaviours, we were really looking at the individual, at the family unit, at the choices they we’re making, that may be dictated by culture, socioeconomic factors and what’s available to you.

Green tea can be a good source of antioxidants. Image © Alessandro Martini. Creative Commons Zero, Public Domain Dedication.

ScienceVega: Why is there a geographical difference to drinking tea, which reduces the risk of stroke in China and South America, but raises it in south Asia?

AS: In the analysis that we did for this study, we did include in our statistics other cardiovascular risk factors (for example, diabetes) and we had a similar number of case and controls from each country or region. Tea intake varied a lot between different regions, for instance, and one of the variables is the proportion of people in the country who are drinking tea in the first place. Tea is very common in China, for example, but it’s almost non-existent in South America where coffee is almost ubiquitous. And then when you break that down further into looking at the types of tea, in China it was mostly green tea or other types of tea, whereas in the UK and Ireland, the majority was black tea. Green tea and black tea are essentially the same plant, but they are processed differently and therefore oxidise differently, which means that as you go from green tea to black tea to others, that impacts the level of antioxidants, or potentially beneficial compounds that are in the tea, which then perhaps starts to explain a little bit as to why we see differences between regions. Secondly, and specifically for tea, if you’re adding things to it, that makes a big difference. In Ireland the vast majority of black tea is consumed with milk or with some kind of non-dairy substitute. Whereas if you look at green tea, it’s very rarely got milk added to it. The additions are going to be different and the types and levels of what you add makes a difference. When we divided people into whether they added milk or not, across the whole world, the reduced chance of stroke with tea somewhat disappeared.

Adding things to tea is probably blocking some of the positive effects of the antioxidants and other beneficial things that are in the tea. The same logic applies to coffee if you’re adding lots of sugar or syrup or milk.

Professor Andrew Smyth

Professor of Clinical Epidemiology

University of Galway.

and

Consultant Physician 

Galway University Hospitals.

The findings come from two analyses of the INTERSTROKE research project which have been published – the effects of fizzy drinks, fruit juice/ drink and water; and the findings related to tea and coffee both of which were published in the International Journal of Stroke.

A series of findings have been released as part of the wider INTERSTROKE project and can be accessed here.