New research is challenging previous medical notions that "apple-shaped" people with more fat around their waist are at higher risk of heart attacks and strokes than "pear-shaped" people with fatter bottoms and hips.

A study of 220,000 people published on Friday confirmed that being obese -having a body mass index (BMI) of 30 or more - is a major risk factor for heart disease, but found the distribution of fat on the body has no impact on that risk.

"Regardless of how you measure it, being obese is bad for your heart. This study suggests that measuring your waist is no better than calculating your BMI," says Mike Knapton, associate medical director at the British Heart Foundation charity, which part-funded the study.

BMI is widely used by researchers and doctors to determine people's health risks. It is calculated by dividing weight in kilograms by height in meters squared. A person who is 165 cm has a BMI of 25 and is classified as overweight at 68 kg, and has a BMI of 30 and is classified as obese at 82 kg.

According to researchers writing in The Lancet medical journal, previous studies have suggested that people with "central obesity" - often described as apple-shaped people - have a three times greater risk of heart attack than people with general obesity as measured by BMI. But other experts have questioned those findings, so a large international consortium of scientists set out to try and settle the issue.

Their results suggest that while monitoring weight and fat levels may be important to try to get people to change their lifestyles, the best predictors of future heart risk are measures of blood pressure, cholesterol and history of diabetes.

The Lancet study involved taking weight, hip, waist, blood pressure, cholesterol and other key data from more than 220,000 adults - who had no previous history of heart disease - and tracking them for almost a decade. During that time, around 14,000 of them had heart attacks or strokes.

John Danesh of Britain's Cambridge University, one of the almost 200 scientists from 17 countries who worked on the study, says the findings showed that "basically, all obesity types are broadly as bad as each other" when it comes to heart health.

Danesh says the findings should help guide medical practice worldwide because at the moment, national and international guidelines provide differing recommendations about the value of assessing obesity levels to predict future heart risk.

"This study very clearly shows that if conventional risk factors (such as blood pressure and cholesterol) have already been measured, then measures of levels of fat add very little," he says.

Obesity has become a global epidemic, with more than half a billion people, or one in 10 adults worldwide, now considered obese - more than double the number in 1980.

Cardiovascular diseases - which can lead to heart attacks, strokes and other fatal events - are the top cause of death worldwide, killing around 17.1 million people a year, according to the World Health Organization (WHO).