The silent but deadly cervical cancer is more common among poor women because they begin sex earlier than their more affluent counterparts, a new report says.

Until now, experts thought that the difference in cases of the disease could be just because poorer women were less likely to go for cervical screening. However, researchers from the International Agency for Research on Cancer (IARC) investigated the link between deprivation and higher cervical cancer risk.

IARC's Silvia Franceschi, who led the study said: "We weren't sure why cervical cancer is more common in poorer women. We now think that it's because in our study, poorer women had become sexually active on an average four years earlier."

Cervical cancer is caused by the sexually transmitted HPV (Human Papillomavirus) virus and usually has no obvious symptoms, except in its later stages. The sypmtoms include abnormal bleeding, vaginal discharge and painful intercourse.

The latest study looked at many countries without screening programmes and found that poorer women were still more likely to develop the disease, an IARC release said.

Researchers found that less educated women were more likely to develop cervical cancer than educated women.

The study also showed that the age at which a woman starts having sex and the age at which she has her first baby are the most important factors explaining this increased risk.

Franceschi suggested that this exposure to HPV at an earlier age may give the virus "more time to produce the long sequence of events that are needed for cancer development."