Stroke: World’s second leading cause of death

Stroke is the second leading cause of death around the world and the third leading cause of disability-adjusted life-years, which is the number of years lost due to ill-health, disability or early death.

In a study into the global burden of strokes, researchers found that between 1990 and 2010, the number of stroke-related deaths increased by 26%.

A systematic review of 56 population-based studies of the incidence and early case fatality of strokes, published from 1970 to 2008, showed that in 10 low-income and middle-income countries, the age-adjusted incidence of stroke more than doubled – from 52 per 100,000 person-years in 1970–79 to 117 per 100,000 person years in 2000–08 – an increase of 5.6% a year.

Yet the incidence of stroke in 18 high-income countries almost halved, from 163 to 94 per 100,000 person-years, a decrease of 1% per year.

The researchers say these data suggest divergent patterns of stroke epidemiology in different socioeconomic regions of the world but that they might also be subject to selection or sampling bias because of sampling only 10 of the world's low-income and middle-income countries over four decades.

Writing in The Lancet Global Health journal, researchers from the Global Burden of Diseases, Injuries, and Risk Factors Study and the Stroke Expert Group estimated the incidence, mortality, and years lost to strokes in all 21 regions of the world in 1990, 2005 and 2010.

The investigators derived the estimates from a systematic review of all relevant studies published over that period and found 119 studies where the pathological subtypes of stroke were confirmed by brain imaging or autopsy in at least 70% of cases.

Surprisingly, the major finding was that in 2010, most of the global burden of strokes was due to haemorrhagic, not ischaemic, strokes (Ischaemic strokes are caused by interruption of the blood supply to the brain, while haemorrhagic strokes result from the rupture of a blood vessel in the brain; and about 87% of strokes are normally caused by ischaemia, the remainder by haemorrhage).

Yet in The Lancet study, the researchers found that haemorrhagic strokes constituted nearly a third of the 16.9 million incident stroke events (20% in the high-income countries and 37% in the low-income and middle income countries).

They say that this is higher than had previously been realised. But despite being only half as common as ischaemic strokes, haemorrhagic strokes caused more than half of the 5.9 million stroke-related deaths, and 61.5% of the 102.2 million lives lost early throughout the world.

“The years of life lost were greater with haemorrhagic stroke because it affected people at a younger age than did ischaemic stroke and had a higher case fatality,” the researchers say.

“The second major finding is that most of the burden of ischaemic and haemorrhagic stroke is in low-income and middle-income countries, which bear 63% of incident ischaemic strokes and 80% of haemorrhagic strokes. The average age of incident and fatal ischaemic and haemorrhagic strokes was six years younger in low-income and middle-income countries than in high-income countries.”

The researchers say their results suggest that key priorities in the quest to reduce the global and regional burden of strokes are prevention of haemorrhagic strokes, particularly in low-income and middle-income countries, and in people younger than 75 years.

Most haemorrhagic strokes can be attributed to hypertension and an unhealthy lifestyle such as physical inactivity, obesity, an unhealthy diet, alcohol excesses and smoking, they write.

“Population-based mass strategies to reduce consumption of salt, calories, alcohol and tobacco by improving education and the environment will complement high-risk strategies of identifying those at risk of haemorrhagic (and ischaemic) stroke,” the researchers say, adding that this will “empower these individuals to improve their lifestyle behaviours and, if necessary, lower their mean blood pressure and blood pressure variability with appropriate doses of antihypertensive drugs”.