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How diet and air pollution impact stroke risk and cardiovascular health

Priscilla Lynch reviews the findings of two new major studies published in European Society of Cardiology journals, which highlight the impact of diet and air pollution on stroke and cardiovascular health

Study of 418,000 Europeans finds different foods linked to different types of stroke

Different types of food are linked to risks of different types of stroke, according to the largest study to investigate this, published in the European Heart Journal recently.

Until now, most studies have looked at the association between food and total stroke, or focused on ischaemic stroke only. However, the current study of more than 418,000 people in nine European countries investigated ischaemic stroke and haemorrhagic stroke separately.

The study found that while higher intakes of fruit, vegetables, fibre, milk, cheese or yoghurt were each linked to a lower risk of ischaemic stroke, there was no significant association with a lower risk of haemorrhagic stroke. However, greater consumption of eggs was associated with a higher risk of haemorrhagic stroke, but not with ischaemic stroke.

About 85 per cent of strokes are ischaemic and 15 per cent are haemorrhagic. Stroke is the second-leading cause of deaths worldwide.



Dr Tammy Tong, the first author of the paper and a nutritional epidemiologist at the Nuffield Department of Population Health, University of Oxford, UK, said: “The most important finding is that higher consumption of both dietary fibre and fruit and vegetables was strongly associated with lower risks of ischaemic stroke, which supports current European guidelines. The general public should be recommended to increase their fibre and fruit and vegetable consumption if they are not already meeting these guidelines.

“Our study also highlights the importance of examining stroke subtypes separately, as the dietary associations differ for ischaemic and haemorrhagic stroke, and is consistent with other evidence, which shows that other risk factors, such as cholesterol levels or obesity, also influence the two stroke subtypes differently.”

The total amount of fibre (including fibre from fruit, vegetables, cereal, legumes, nuts and seeds) that people ate was associated with the greatest potential reduction in the risk of ischaemic stroke. Every 10g more intake of fibre a day was associated with a 23 per cent lower risk, which is equivalent to around two fewer cases per 1,000 of the population over 10 years.

Fruit and vegetables alone were associated with a 13 per cent lower risk for every 200g eaten a day, which is equivalent to one less case per 1,000 of the population over 10 years. No foods were linked to a statistically significant higher risk of ischaemic stroke.

The European Society of Cardiology (ESC) and the World Health Organisation Regional Office for Europe recommend consuming at least 400g of fruit and vegetables a day; the ESC also suggests people should consume 30-to-45g of fibre a day.

The researchers found that for every extra 20g of eggs consumed a day, there was a 25 per cent higher risk of haemorrhagic stroke, equivalent to 0.66 extra cases per 1,000 (or around two cases per 3,000) of the population over 10 years. An average large-sized egg weighs approximately 60g. Egg consumption in the EPIC study was low overall, with an average of less than 20g eaten a day.

The researchers say the associations they found between different foods and ischaemic and haemorrhagic stroke might be explained partly by the effects on blood pressure and cholesterol.

Dr Tong and her colleagues analysed data from 418,329 men and women in nine countries (Denmark, Germany, Greece, Italy, The Netherlands, Norway, Spain, Sweden and the UK) who were recruited to the European Prospective Investigation into Cancer and Nutrition (EPIC) study between 1992 and 2000.

The participants completed questionnaires asking about diet, lifestyle, medical history and socio-demographic factors, and were followed-up for an average of 12.7 years. During this time, there were 4,281 cases of ischaemic stroke and 1,430 cases of haemorrhagic stroke.

Food groups studied included meat and meat products (red meat, processed meat and poultry), fish and fish products (white fish and fatty fish), dairy products (including milk, yogurt, cheese), eggs, cereals and cereal products, fruit and vegetables (combined and separately), legumes, nuts and seeds, and dietary fibre (total fibre and cereal, fruit and vegetable fibre).

Major strengths of the study include the large numbers of people studied in several different countries and long follow-up period. Most types of food were included in the study, although information on diet was collected at only one point in time, when the participants joined the study. As the study is observational, it cannot show that the foods studied cause an increase or decrease in risk of ischaemic or haemorrhagic stroke, only that they are associated with different risks. Information on medication use (including statins) was not available.

Reference: The associations of major foods and fibre with risks of ischaemic and haemorrhagic stroke: A prospective study of 418,329 participants in the EPIC cohort across nine European countries, by Tammy Tong et al. European Heart Journal 2020. doi:10.1093/eurheartj/ehaa007.

Cardiovascular deaths most affected by air pollution — landmark study

Air pollution is responsible for shortening people’s lives worldwide on a scale far greater than wars and other forms of violence, parasitic and vector-born diseases such as malaria, HIV/AIDS and smoking, according to a new study published in Cardiovascular Research.

Using a new method of modelling the effects of various sources of air pollution on death rates, the researchers estimated that globally, air pollution caused an extra 8.8 million premature deaths a year in 2015. This represents an average shortening of life expectancy of nearly three years for all persons worldwide.

The researchers looked at the effect of air pollution on six categories of disease: Lower respiratory tract infection; chronic obstructive pulmonary disease; lung cancer; heart disease; cerebrovascular disease leading to stroke; and other, non-communicable diseases, which include conditions such as high blood pressure and diabetes. They found that cardiovascular diseases (heart disease and cerebrovascular disease combined) are responsible for the greatest proportion of shortened lives from air pollution: 43 per cent of the loss in life expectancy worldwide.

They also found that air pollution had a greater effect on shortening lives in older people, with the exception of deaths in children aged under five in low-income countries such as Africa and South Asia.

Globally, about 75 per cent of deaths attributed to air pollution occur in people aged over 60 years.

This is the first study to show the effects of air pollution on deaths according to age, type of disease and also its effect on life expectancy at the level of individual countries and regions.

Professors Jos Lelieveld and Thomas Münzel, of the Max Planck Institute for Chemistry and the Department of Cardiology of the University Medical Centre Mainz in Mainz, Germany, who led the research, said the findings suggest the world is facing an air pollution “pandemic”.

Prof Münzel said: “Policy-makers and the medical community should be paying much more attention to this. Both air pollution and smoking are preventable, but over the past decades, much less attention has been paid to air pollution than to smoking, especially among cardiologists.

“In this paper, we distinguished between avoidable, human-made air pollution and pollution from natural sources such as desert dust and wildfire emissions, which cannot be avoided. We show that about two-thirds of premature deaths are attributable to human-made air pollution, mainly from fossil fuel use; this goes up to 80 per cent in high-income countries. Five-and-a-half million deaths worldwide a year are potentially avoidable.

“It is important that policy-makers and the medical community realise that air pollution is an important risk factor for heart and blood vessel disease. It should be included as a risk factor, along with smoking, diabetes and high blood pressure and cholesterol, in the guidelines of the European Society of Cardiology and the American Heart Association on the prevention of acute and chronic heart syndromes and heart failure.”

Prof Lelieveld noted that air pollution causes damage to the blood vessels through increased oxidative stress, which then leads to increases in blood pressure, diabetes, stroke, heart attacks and heart failure.

The researchers estimate that if air pollution was reduced by removing fossil fuel emissions, the average life expectancy worldwide would increase by just over a year, and by nearly two years if all human-made emissions were removed.

However, there are large differences between regions due to the diversity in emissions. In East Asia, which has the highest loss of life expectancy due to avoidable air pollution, three of the average of four years of lost life expectancy could be prevented by the removal of human-made emissions; whereas in Africa, where population growth is rapid and pollution from dust predominates, only 0.7 of 3.1 years lost could be prevented. In Europe, there is an average of 2.2 years of lost life expectancy, 1.7 of which could be prevented, and in North America there is an average of 1.4 years of lost life expectancy, of which 1.1 could be prevented, mostly by phasing-out fossil fuels.

The researchers used exposure data from a model that simulates atmospheric chemical processes and the way they interact with land, sea and chemicals emitted from natural and human-made sources such as energy generation, industry, traffic and agriculture. They applied these to a new model of global exposure and death rates and to data from the Global Burden of Disease, which included information on population density, geographical locations, ages, risk factors for several diseases and causes of death. They estimated the death rates and loss of life expectancy from different causes of air pollution compared to other causes of premature death for countries and regions around the world.

Limitations of the study include the fact that there is uncertainty surrounding the estimates, so the size of the effect of air pollution on deaths could be larger or smaller. Nevertheless, such uncertainty also applies to other health risk factors, including smoking. More research is needed to understand fully the mechanisms involved in the associations seen between air pollution and a variety of diseases.

Reference: Loss of life expectancy from air pollution compared to other risk factors: A worldwide perspective, by Jos Lelieveld et al. Cardiovascular Research 2020. doi:10.1093/cvr/cvaa025.

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