Washington: Each five-unit increase in BMI raises incidence of heart disease in women by 23 per cent, a study has claimed. A team of researchers from Oxford University followed the health of 1.2 million women in England and Scotland with an average age of 56, over the course of a decade.

They found that on average, one in eleven lean, middle aged women with an average BMI of 21 are going to be hospitalized or die of heart related disease between the ages of 55 and 74, media reported. The study also found that as women's BMI increased, so did the risk of heart disease reaching one in six for obese women, whose BMI was 34 on average.

According to the World Health Organization, a "normal" BMI is between 18.5 and 25 but the research found that even within this range; the risk of developing heart disease grew steadily higher as BMI increased.

The risk of dying from heart disease was lowest at BMIs between 20 and 25, then increased steadily until 32.5 when it began to accelerate much more rapidly.

Dr Dexter Canoy, who led the study, said that the risk of developing CHD was raised even with small incremental increases in BMI, and this is seen not only in the heaviest but also in women normally not considered obese.

He said that small changes in BMI, together with leading a healthy lifestyle by not smoking, avoiding excess alcohol consumption, and being physically active could potentially prevent the occurrence of CHD for a large number of people.

The study has been published in the BMC Medicine journal.