Widening Ethnic Inequalities in Stroke Incidence: A 30-Year Population-Based Analysis of the South London Stroke Register

This 30-year population-based study reveals that while overall stroke incidence in South London initially declined, recent sharp increases driven by Black-African and Black-Caribbean populations have reversed earlier progress, resulting in widening ethnic inequalities that persist even after adjusting for socioeconomic status.

The Gist

Imagine the human body as a city, and a stroke as a sudden, catastrophic traffic jam that stops the flow of life (blood) to a specific neighborhood (the brain). For decades, researchers have known that this traffic jam happens more often and at younger ages in certain ethnic neighborhoods compared to others.

This paper acts like a 30-year time-lapse camera, watching South London from 1995 to 2024 to see how these traffic jams changed over time for different groups of people.

Here is the story the data tells, broken down into simple concepts:

1. The Big Picture: A Rollercoaster Ride

For the first 25 years of the study, the city was getting safer. The number of strokes dropped significantly, like a city successfully fixing its potholes and traffic lights. However, in the last five years (2020–2024), the trend flipped. The number of strokes started climbing again.

The Twist: This rise wasn't happening everywhere equally.

• The White population: Their stroke rates stayed relatively flat or continued to drop slightly.
• Black African and Black Caribbean populations: Their stroke rates didn't just stay high; they spiked.

2. The "Gap" is Getting Wider

Imagine two runners on a track. For a while, the gap between them seemed to shrink. But recently, the runner in the lead (the White population) slowed down or stopped, while the other runner (Black African and Black Caribbean populations) actually sped up.

• The Result: The gap between these groups is now wider than it has been in decades.
• The Numbers: In the most recent period, Black African people were 2.3 times more likely to have a stroke than White people, and Black Caribbean people were 2 times more likely. This is a much bigger difference than we saw 30 years ago.

3. The "Younger" Problem

Think of a clock. For White people, the "stroke clock" usually starts ticking loudly in their 70s. For Black African people, that clock starts ringing much earlier, often in their late 50s or early 60s.

• The study found that Black African people are having their first stroke about 12 years earlier than their White neighbors.
• This means they are losing a decade of life before the "typical" retirement age.

4. The "Deprivation" Factor (The Neighborhood Effect)

The researchers asked: "Is this just about money? If we look at rich and poor people within the same ethnic group, does the gap disappear?"

• The Answer: No.
• The Analogy: Imagine two houses. One is in a poor neighborhood, one in a rich one. If you live in a poor neighborhood, your risk of a stroke goes up, no matter who you are.
• The Double Whammy: However, being Black and living in a deprived (poor) area creates a "double whammy." The risk is highest for Black African and Black Caribbean people living in the most deprived areas.
• The Reality: Even when researchers adjusted for poverty, the ethnic gap remained. Being Black in this city still carries a higher risk, suggesting that factors beyond just income—like systemic barriers, stress, or how healthcare is delivered—are at play.

5. The "Type" of Crash

Not all traffic jams are the same. Some are blockages (Ischaemic), and some are burst pipes (Haemorrhagic).

• The study found that the inequalities were most severe for burst pipes (Primary Intracerebral Haemorrhage).
• Black African and Black Caribbean populations had significantly higher rates of this specific, often more dangerous, type of stroke compared to White populations.

6. Why is this happening? (The "Why" behind the "What")

The paper suggests that while we have tools to prevent strokes (like managing blood pressure and diabetes), these tools aren't reaching everyone equally.

• The "Too Late" Alarm: Current health checks in the UK often start at age 40. But for Black African populations, the risk starts building much earlier. It's like checking your car's engine only after the warning light has been flashing for years.
• The "Trust" Barrier: The paper notes that historical mistrust in healthcare and unequal treatment (like not getting strong enough medication for high blood pressure) contribute to the problem.
• The Pandemic Effect: The recent rise in strokes coincides with the pandemic, which disrupted healthcare. The study suggests that Black and deprived communities were hit harder by these disruptions, losing access to the routine care that keeps blood pressure in check.

The Bottom Line

The paper concludes that we cannot just say "we are all getting older" or "poverty is the only cause." The gap is widening because the specific groups that need help the most (Black African and Caribbean communities, especially those in poor areas) are falling further behind.

To fix this, the authors argue we need to:

1. Start the clock earlier: Check for risks in younger people (before age 40) in high-risk groups.
2. Fix the "Double Whammy": Target prevention programs specifically at the intersection of ethnicity and poverty.
3. Build Trust: Ensure that healthcare systems treat these communities fairly and effectively, so that the "traffic lights" work for everyone, not just some.

In short: The city is getting safer for some, but for others, the road is becoming more dangerous, and we need to change how we drive to keep everyone safe.

Technical Summary

Technical Summary: Widening Ethnic Inequalities in Stroke Incidence: A 30-Year Population-Based Analysis of the South London Stroke Register

Problem Statement
While ethnic inequalities in stroke incidence are well-documented, long-term trends over three decades and the specific impact of socioeconomic status (SES) on these disparities remain understudied. Previous research has established that minority ethnic groups, particularly Black populations, experience higher and earlier stroke incidence compared to White populations in high-income countries. However, it remains uncertain whether these inequalities have narrowed or widened over time, and to what extent socioeconomic deprivation explains these ethnic disparities. This study addresses the gap in long-term surveillance data by analyzing stroke incidence from 1995 to 2024 in a multi-ethnic urban population.

Methodology
The study utilized data from the South London Stroke Register (SLSR), a prospective, population-based cohort established in 1995 covering the London boroughs of Lambeth and Southwark.

• Study Population: The analysis included 7,726 residents aged ≥18 years with a first-ever stroke registered between January 1, 1995, and December 31, 2024.
• Case Ascertainment: Cases were identified through multi-source surveillance (hospitals, community sources, death certificates) and confirmed by clinicians using WHO ICD-10 criteria. Capture-recapture analysis previously indicated 88% ascertainment.
• Exposure and Outcomes: Ethnicity was self-reported using UK Office for National Statistics (ONS) categories, specifically distinguishing between Black African and Black Caribbean groups. The primary outcome was the age- and sex-standardized incidence rate of first-ever stroke per 100,000 person-years, calculated for all strokes and subtypes (ischemic, primary intracerebral haemorrhage [PICH], and subarachnoid haemorrhage [SAH]).
• Socioeconomic Status (SES): SES was measured using the area-level Index of Multiple Deprivation (IMD) quintiles, assigned based on the patient's Lower Super Output Area (LSOA) at the time of stroke onset.
• Statistical Analysis: Standardized incidence rates were calculated using the 2013 European Standard Population. Poisson regression models were employed to estimate Incidence Rate Ratios (IRRs) comparing ethnic minority groups to the White population, adjusting for age, sex, and IMD. Interaction terms between ethnicity and IMD were tested to assess whether the effect of deprivation varied by ethnicity. Marginal incidence rates were derived using the emmeans package, weighted by the observed age-sex distribution.

Key Results

• Temporal Trends: Overall standardized stroke incidence decreased by 34% between the 1995–1999 period and the 2010–2014 period (from 198 to 131 per 100,000). However, this trend reversed, with a 13% increase observed in the 2020–2024 period (rising to 152.7 per 100,000).
• Ethnic Disparities: Throughout the 30-year period, Black African and Black Caribbean populations consistently exhibited higher incidence rates than the White population.
  • In 1995–1999, the IRR for Black African vs. White was 1.57 (95% CI 1.23–2.00) and for Black Caribbean vs. White was 1.52 (95% CI 1.31–1.77).
  • By 2020–2024, these inequalities had widened significantly. The IRR for Black African vs. White increased to 2.31 (95% CI 2.03–2.62), and for Black Caribbean vs. White to 2.00 (95% CI 1.73–2.31).
  • The widening of inequalities for Black African populations between 2015–2019 and 2020–2024 was statistically significant (Ratio of IRRs = 1.30, p=0.01).
• Stroke Subtypes: Inequalities were consistent across subtypes but most pronounced for primary intracerebral haemorrhage (PICH). By 2020–2024, PICH incidence was 3.04 times higher in Black African and 2.59 times higher in Black Caribbean populations compared to White populations.
• Role of SES: Adjustment for IMD attenuated but did not eliminate ethnic inequalities. In 2020–2024, the adjusted IRR for Black African vs. White dropped from 2.31 to 2.03, and for Black Caribbean from 2.00 to 1.79.
• SES Gradients: Clear socioeconomic gradients existed within all ethnic groups, with steeper gradients observed among Black populations. In the most deprived quintile (IMD 1), Black African populations had the highest incidence (191.4 per 100,000).
• Age at Onset: Black African populations experienced their first stroke significantly earlier than White populations. In 1995–1999, the mean age was 58.6 years for Black African vs. 73.6 years for White. By 2020–2024, this gap narrowed to 9 years (61.6 vs. 70.1 years), though the difference remained significant.

Significance and Claims
The paper claims to extend existing evidence in three specific ways:

1. Long-term Quantification: It provides a quantification of how ethnic inequalities in stroke incidence have evolved over three decades using consistent methods and complete case ascertainment in a multi-ethnic UK population.
2. Widening Inequalities: It demonstrates that ethnic inequalities not only persisted but widened over time, particularly in the most recent five-year period, driven by rising incidence in Black African and Black Caribbean populations while rates in the White population remained stable or declined.
3. Joint Impact of Ethnicity and Deprivation: By incorporating SES gradients through interaction analyses, the study shows that ethnicity and deprivation act jointly rather than independently. Groups facing both disadvantages (e.g., Black African populations in the most deprived areas) experience the highest stroke incidence. This is reported as the first time such an interaction has been documented in the UK context.

The authors conclude that current prevention frameworks, such as the NHS Health Checks programme starting at age 40, may be failing to reach high-risk groups who develop stroke 10–12 years earlier than the general population. They argue that achieving equity requires ensuring the uptake of cardiovascular risk programmes across all socioeconomic and ethnic groups and implementing earlier risk management for these specific populations.