Junk food 'fuelling stroke crisis for young people'

Young people who binge on fast food are "at risk of developing a stroke", according to a Daily Express report.

This news is based on a large study carried out in the US that examined trends in stroke over the course of a decade. It found that the overall rate of stroke decreased over time, but that the proportion of stroke patients under the age of 55 increased during this time significantly.

This suggests that stroke, previously thought a condition belonging to the elderly, is now increasingly a middle-aged health problem too.

Researchers found a corresponding rise in risk factors related to bad diet such as high cholesterol and high blood pressure. However, while it is easy to speculate what is driving this pattern towards younger people having a stroke, the claim that bingeing on fast food has directly fuelled the trend is not supported by the data presented by this study.

The results may also not necessarily apply to the UK as rates of obesity are higher in the US. However, data collected by the NHS in England shows a similar rise. From 1998 to 1999 there were 9,321 people under the age of 55 admitted to hospital due to a stroke. This figure rose to 16,415 during 2010 to 2011.

This study also found a stark difference in stroke rates between the white and black populations, and the reasons for this – whether genetic or socioeconomic – are worthy of further investigation.

Where did the story come from?

The study was carried out by researchers from the University of Cincinnati College of Medicine and Cincinnati Children’s Hospital Medical Center in the US. The research was funded by the US National Institutes of Health.

The study was published in the peer-reviewed journal Neurology.

The results of the study were covered accurately by BBC News and the Express. However, some news coverage made the seemingly reasonable assumption of a direct cause and effect (causal) relationship between junk food and the observed trend in stroke rates, but is not supported by the research.

What kind of research was this?

The researchers carried out a time trend study to examine changes in the number and characteristics of first-time strokes between 1993 and 2005. They conducted the study in the Greater Cincinnati/Northern Kentucky region of the US. Data was collected at three different points in time: 1993-1994, 1999 and 2005.

While time trend studies can bring to light changing patterns in a population, and help generate hypotheses for future research, they can’t tell us what factors cause the observed changes.

What did the research involve?

The Greater Cincinnati and Northern Kentucky region has a population of approximately 1.3 million people (roughly the population of Glasgow). The researchers examined death certificates, medical records of all the area hospitals and other healthcare records to identify cases of stroke. They only included cases of first-ever stroke in people over the age of 20 during three distinct periods (1993-1994, 1999 and 2005).

Using medical records, the researchers collected data on stroke symptoms, medical and social history, medication use and other patient characteristics.

The researchers calculated the incidence rate, or number of new cases of stroke over time, across the population and examined changes in this rate over the study period. They then calculated age-, race- and gender-specific rates, making adjustments so that the rates in populations with different age structures, for example, could be directly compared.

The study authors also collected information on stroke risk factors among people aged 20 to 54, and examined trends in these factors over time. They collected this data from the wider study population and also identified stroke patients within the region. To do this, they used data from telephone surveys conducted in 1995, 2000 and 2005. This included data on several known risk factors, including hypertension, diabetes, high cholesterol, coronary heart disease and smoking. Regional data on obesity, an important risk factor for stroke, was not available for all periods.

Finally, the researchers also collected data on a number of diagnostic tests, including rates of first-ever stroke patients undergoing computed tomography (CT) and magnetic resonance imaging (MRI) scans.

What were the basic results?

The authors found that the number of first-ever strokes in people over the age of 20 years old was:

• 1,942 in 1993-1994
• 2,034 in 1999
• 1,916 in 2005

Of these patients, the proportion of first-ever strokes in people under the age of 55 increased significantly between 1993-1994 and 2005. This proportion was:

• 12.9% in 1993-1994
• 13.3% in 1999
• 18.6% in 2005

Overall, the average age of first-ever stroke significantly decreased during the study period. Across the course of the study, the average age of stroke patients was:

• 71.2 years in 1993-1994
• 72.1 years in 1999
• 69.2 years in 2005

The researchers also found that black people were more likely to experience a stroke than white people. In 2005, 128 per 100,000 people in black populations experienced a stroke compared with 48 per 100,000 in white populations.

Over time, the researchers found:

• significant increases in the number of people reporting high cholesterol
• no significant differences in the number of people with high blood pressure, diabetes, coronary heart disease or smokers

When examining time trends in risk factors among participants who had suffered a stroke, the researchers found:

• significant increases in the number of stroke patients reporting coronary heart disease
• no significant differences in the number of stroke patients with high blood pressure, diabetes, high cholesterol or who were smokers

When the researchers analysed data on the use of CT and MRI scans in first-ever stroke patients, they found that:

• There was no significant difference in CT scans over the course of the study.
• There was a significant increase in MRI scans over the course of the study, across all ages, with 18% undergoing an MRI in 1993-1994 compared with 27% in 1999 and 58% in 2005.
• There was a significant age difference in the percentage of patients undergoing a stroke, where younger patients were more likely to have the scan in 2005 compared with other time periods.

How did the researchers interpret the results?

The researchers concluded that between 1993 and 2005 there was a significant increase in the proportion of stroke patients under the age of 55. They said that overall, stroke incidence has been found to be declining, and any decline “is positive from a public health prospective, but reduced incidence in older ages is counterbalanced by the worrisome trend of younger strokes with substantial productive life years lost and immense healthcare expenses over time”.

Conclusion

This large population-based study indicates that among people having a first-time stroke, the proportion made up of people under the age of 55 is increasing. Unfortunately, this study cannot tell us conclusively what is causing such an increase.

The researchers said: “The reasons for our incidence trends are not clear,” but went on to discuss several trends that may have contributed to the observed increase in stroke among younger people, including:

• increasing rates of drug abuse during the study period
• increases in the number of young people with coronary heart disease among young stroke patients
• trend towards increasing cases of diabetes and high cholesterol, although these were not statistically significant in the study population

They said that: “increasing stroke risk factors in the young should lead to earlier strokes, assuming that stroke is often the end result of sustained risk factors”. They suggested, however, that “stroke prevention treatments may have been applied preferentially to the elderly where physicians expect stroke to occur, and less so in younger adults where stroke is considered unlikely”, and that “this may partially explain trends in incidence seen over time, but it is not possible to make causal inferences from our population-level data”.

Finally, the authors discussed the possibility that the increasing proportion of strokes in younger people may be the result of changing medical technology.

They said that their “data show substantially increased MRI use over time, and younger patients were more likely to receive MRI than older patients”. It may be the case that, in the “pre-MRI era”, some strokes in younger people were misdiagnosed.

Applying these results to a UK population should be done with caution. While the UK and US share many social, economic and demographic variables, there are differences between the populations that may limit the possibility of generalising the study’s findings.

One of the inherent weaknesses of a time trend study is that it can never prove a direct cause and effect association between risk factors and disease. It can only highlight trends.

But knowing what we do, both about risk factors for stroke and changes to Western lifestyles, it is not unreasonable to assume that factors such as poor diet, obesity and lack of exercise are placing more middle-aged people at risk of stroke.

This study could suggest that none of us should be complacent about our own personal stroke risk, whatever age we are. The best advice is to take steps to reduce this risk, such as quitting smoking if you smoke, eating a healthy diet and taking regular exercise.

Read more about reducing your stroke risk.