It is clear that oral contraceptives increase a woman's risk of developing breast cancer

Dr Merethe Kumle, study co-ordinator

However, the highest increased risk (144%) was among women aged over 45 who were still using the Pill.

Dr Merethe Kumle, who carried out the research, said: "It is clear that oral contraceptives increase a woman's risk of developing breast cancer, particularly when they are used in the later period of reproductive life."

The study, presented at the third European Breast Cancer Conference in Barcelona, used data collected from 103,000 women aged between 30 and 49.

Dr Kumle from the Institute of Community Medicine in Tromso, Norway, collaborated with researchers in Sweden and France to assess data from the Women's Lifestyle and Health study carried out in Norway and Sweden.

The women were originally contacted in 1991/92 and followed through to December 1999.

During that time, 1,008 cases of breast cancer had been detected.

Most of the women who had taken the Pill had used the more modern brands that are currently prescribed by doctors.

Lower dose Pills

Dr Kumle stressed the Pill also has health benefits.

She said: "Oral contraceptives have a lot of advantages as well as disadvantages.

"The total number of deaths from any cause among women who use oral contraceptives is likely to be lower than women who have never used the Pill - just as with hormone replacement therapy."

She added: "The Pill has made it possible for women to decide when and how many children they will give birth to - something which has revolutionised women's lives and is an important issue in women's rights."

The absolute risk of a woman developing breast cancer under the age of 40 is very low, says Dr Kumle.

She also stressed that modern oral contraceptives have much lower hormone doses in them than the older ones, which caused an unacceptably high number of adverse effects.

Professor Valerie Beral, who is head of Cancer Research UK's Cancer Epidemiology Unit in Oxford, said this study was in line with previous research, although the figures differed.

She said: "We have done a study of 54,000 women with breast cancer and found there is a small increased risk of developing the disease from taking the Pill.

Breast cancer trends

"We found a 24% increase in risk while women were currently taking the Pill.

"However the risk fell away to the same as women who had never taken the Pill, within 10 years of them discontinuing its use."

The incidence of breast cancer has been rising in Western countries over the past 30 years.

The use of oral contraceptives is one reason, but girls starting their periods earlier, women having fewer and later births, later menopause and a tendency to being overweight are also influential.

Dr Kumle said: "We found a slightly increased risk of breast cancer among users of the Pill, but it is important to underline that young women using the Pill are not playing hazard with their health.

"As contraception, the Pill should still be the drug of choice for young women."