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Global stats show rise in strokes in younger people

“Strokes in under 64s soar by 25%,” reports the Daily Mail.

The headline was prompted by a major study looking at stroke statistics from across the world.

A striking finding is that strokes in the 20–64 age group, for example, now make up nearly a third of the total number of strokes compared with a quarter in 1990. This led the research team to write that “stroke should no longer be regarded as a disease of old age”.

The overall amount of disability, illness and premature death caused by stroke is also projected to more than double by 2030. This caused The Independent to warn of a “looming stroke epidemic”.

Although this study has some limitations, the results are likely to be reliable, and the figures on strokes among younger people make for worrying reading.

Not all the news is bad, however. For example, death rates from stroke have decreased worldwide in the past two decades, although strokes can often lead to long-term disability.

The study found that there were wide differences in stroke incidence between poor and rich countries, such as the UK, with strokes becoming more widespread in the poorer countries.

They also found that the UK falls behind both Germany and France in terms of mortality rates from stroke, measured against incidence, prompting calls for improvements in acute care.

Where did the story come from?

The study was carried out by an international team of researchers from academic institutions in New Zealand, the US, the UK, South Africa, Denmark, Ireland, Singapore, China and Japan. It was funded by the Bill and Melinda Gates Foundation in the US.

The study was published in the peer-reviewed medical journal The Lancet.

The study was covered fairly in the media, with some reports including comments from independent UK experts. The word “epidemic” was perhaps a little strong as it may imply that strokes are spreading from one person to another.

Also, many headlines used the term “young” in relation to the findings while those affected in the UK may more appropriately be described as “middle-aged”.

What kind of research was this?

This was an analysis of 119 studies looking at stroke statistics in individual countries in the world’s 21 regions during 1990 to 2010. It is part of a major study called the Global Burden of Diseases, Injuries and Risk Factors Study 2010. 

The authors point out that stroke is the second leading cause of death and third most common cause of disability worldwide. However, there have been no estimates assessing and comparing the incidence, prevalence, mortality and disability caused by stroke in most world regions.

What did the research involve?

The authors searched all appropriate databases to identify relevant studies published between 1990 and 2010. The databases used were Medline, Embase, LILACS, Scopus, PubMed, Science Direct, Global Health Database, the WHO library and WHO regional databases from 1990 to 2012.
 
To ensure their analysis was based on high quality studies they established a number of criteria for inclusion. For example, they only included studies that:

  • used WHO’s definition of stroke
  • reported their methods for defining stroke cases
  • distinguished between first-ever and recurrent stroke (only the former were included in these analyses)
  • reported relevant age-specific data in enough detail to enable accurate estimates 

Also, studies from high-income countries had to include complete details of stroke cases (that is, whether they were admitted to hospital or not, whether the stroke was fatal or non-fatal) from several overlapping sources of information.

These included family physicians and other community health services, nursing homes, hospital admissions and discharges, neuroimaging and rehabilitation services and death certificates. Using multiple sources is regarded as best practice for population-based studies.

However, the researchers allowed less rigorous criteria for studies from low-income and middle-income countries in which no other relevant data was otherwise available.

They used a validated analytical technique to calculate estimates of stroke incidence (the number of strokes annually as a proportion of the population), prevalence (proportion of strokes overall) and mortality.

They also looked at disability-adjusted life years (DALYs) lost to stroke. DALYs are a measure of the number of years lost due to ill health, disability or early death, in this case from stroke.

These calculations were made by age group (below 75 years, or 75 years and over) and in total, by country income level (high-income, and low-income and middle-income combined) for 1990, 2005 and 2010.

What were the basic results?

The authors included 119 studies (58 from high-income countries and 61 from low-income and middle-income countries). Below are the main findings on stroke:

  • From 1990 to 2010, the incidence of stroke decreased by 12% (95% Confidence interval (CI) 6–17) in high-income countries, and increased by 12% (-3 to 22) in low-income and middle-income countries. This last increase was not statistically significant.
  • Mortality rates decreased by 37% in high-income (95% CI 31–41) countries and by 20% in low-income and middle-income countries (95% CI 15–30).
  • In 2010, worldwide, there were 16.9 million people who had a first stroke (incident strokes), 33 million stroke survivors (prevalent strokes), 5.9 million stroke-related deaths and 102 million disability adjusted life years (DALYs) lost. These numbers had significantly increased since 1990 (by 68%, 84%, 26% and 12%, respectively).
  • Most of the stroke burden (68.6% incident strokes, 52.2% prevalent strokes, 70.9% stroke deaths and 77.7% DALYs lost) occurred in low-income and middle-income countries.
  • In 2010, 5.2 million (31%) strokes were in children (defined as less than 20 years old) and young and middle-aged adults (20–64 years).
  • 89% of strokes in children and 78% of strokes in young and middle aged adults occurred in low-income and middle-income countries.
  • There were significant differences in overall stroke burden between different regions and countries.
  • More than 62% of new strokes, 69.8% of prevalent strokes, 45.5% of deaths from stroke and 71.7% of DALYs lost because of stroke were in people younger than 75 years.

How did the researchers interpret the results?

The researchers say that although mortality rates from stroke have decreased worldwide in the past two decades, the absolute number of people who have a stroke every year, the number of stroke survivors, related deaths and the overall global burden of stroke (DALYs lost) are “great and increasing”.

Stroke, they point out, has traditionally been seen as a condition affecting elderly people, but the proportion of younger people affected by stroke is increasing and is likely to continue unless effective prevention strategies are implemented.

An editorial accompanying the paper says that a rise in the prevalence of diabetes, unhealthy cholesterol levels, obesity, cigarette smoking, alcohol abuse and the use of illicit drugs may explain the findings for increased stroke among young people.

Despite some improvements in stroke prevention and management in high-income countries, the growth and ageing of the global population is leading to a rise in the overall number of people who have a stroke. Urgent preventive measures and acute stroke care should be promoted in low-income and middle-income countries, the editorial argues.

Conclusion

This study is comprehensive in its global coverage of stroke and is based on the largest stroke dataset available to date. It is also the first to provide systematic regional and country-specific estimates of the burden of the disease. 

As the authors point out, the main limitations include a scarcity of high-quality data from low-income and middle-income countries especially, which may affect the reliability of some of the figures. Other limitations include a potential underestimation of the burden of stroke. This may have come about because “silent strokes”, which are those not based on diagnosis using clinical criteria, and strokes from vascular dementia were not included.

The study has some interesting findings at regional level. For example, in 2010, Australia and parts of Central and South America had the lowest incidence of stroke, followed by Western Europe. Eastern Europe and Asia had the highest incidence. Australia and North America had the lowest death rates from stroke followed by Western Europe.

Within Western Europe, the UK falls behind both Germany and France in terms of mortality rates from stroke, measured against incidence.

Despite an overall reduction in stroke, the findings on younger people are worrying. 

It is impossible, based on the available data, to draw firm conclusions about what is causing this trend. There are several factors that increase risk of stroke, which include smoking, drinking too much, not exercising enough and eating a poor diet.

Read more about stroke.

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