Danish researchers bust popular 'fat myth'
There is no 'obesity paradox' for stroke, study finds.
In recent years, obesity researchers have discussed a strange paradox: overweight and obese people have a greater risk of having a stroke -- but according to statistics, their risk of dying from a stroke is considerably lower than for people within the normal weight range.
New Danish research shows that the paradox is based on a misunderstanding and when a number of factors are taken into account, having extra fat on your body is certainly not an advantage.
“Many doctors have been in doubt about how they should deal with obesity and overweight in stroke patients,” says Christian Dehlendorff, a statistician with the Danish Cancer Society Research Centre, who co-authored the new study. “Obese and overweight people don’t just have a higher risk of strokes, their risk of dying from the stroke is also greater.”
Over 71,000 Danes are in the study
The study is based on information from 71,617 Danish patients who were hospitalised with a stroke. Within a month 5,512 of them had died because of the stroke.
The term stroke (apoplexy) refers to patients with a brain haemorrhage or a blood clot in the brain.
In 85 per cent of stroke cases, the stroke is caused by a blood clot while in 15 per cent the cause is a haemorrhage.
Every year, around 12,000 Danes have either a blood clot or a haemorrhage in the brain.
Among the symptoms are speech disturbances, confusion, and paralysis in the arm, leg or face on one side of the body.
About one in three of the people who have a brain haemorrhage or a blood clot in the brain die within the first year of their stroke.
“While the patients were in hospital their Body Mass Index (BMI) was calculated; then they were placed in one of four groups: underweight, normal weight, overweight and obese,” says Dehlendorff.
“That means we had an opportunity to compare the patients' BMI and see whether fat people had a greater chance of surviving a stroke than people of normal weight,” he says.
Turns out, that wasn’t the case.
Fat people have fewer strokes
Earlier studies on the obesity paradox were revealed to be full of errors because they failed to take one important factor into account: the size of blood clots -- blood clots caused by obesity are not as large as clots caused by other factors.
When the researchers compared the results for fat people and people of normal weight, whose blood clots were precisely the same size, the obesity paradox simply melted away.
In fact, obese people had a higher mortality rate following a blood clot in the brain -- and the mortality rate increased as the overweight of the people increased.
“The misunderstanding -- that fat people recover more quickly after a stroke -- arose because the researchers were not in a position to make corrections for the fact that obese people actually have less severe strokes than people whose stroke is caused by another factor,” says Dehlendorff.
“But we had that opportunity in our study and it was extremely important when we started to calculate the patients' chances of survival.”
Obese people have strokes early on in life
If you are overweight you’re also extra exposed to having a stroke earlier in life, reveals the new study.
“Our study showed that if you are obese you will on average be six years younger when you have a stroke than if your weight is normal,” says Dehlendorff. “Our study certainly did not find any advantages of being fat.”
As well as age and BMI, the researchers also took the following factors into account:
How serious the stroke was.
Whether it was a brain haemorrhage or a blood clot -- a brain haemorrhage is more dangerous.
Risk factors that can lead to cardio-vascular diseases -- including diabetes, hypertension, smoking and alcohol.
- Education and income.
Medical consultant: It makes sense
Dehlendorff believes that their study is robust and good but as is always the case with scientific observation studies, other researchers must corroborate the results. He hopes this will happen.
Jan Kyst Madsen, a medical consultant at the cardiology department of Gentofte Hospital -- who has had nothing to do with the study -- believes that the results can be trusted.
“71,000 apoplexy patients is an unbelievably good database,” he says. “And the study was carried out by both statisticians and neurologists. It looks very, very sensible.”
The scientific study was recently published in JAMA Neurology.
Translated by: Michael de Laine
- Dehlendorff et al. Body Mass Index and Death by Stroke No Obesity Paradox. JAMA Neurol. Published online June 02, 2014. doi:10.1001/jamaneurol.2014.1017