TOKYO - THE monthly discomfort many women see as a curse could pay off someday as Japanese researchers say menstrual blood can be used to repair heart damage.

Scientists obtained menstrual blood from nine women and cultivated it for about a month, focusing on a kind of cell that can act like stem cells.

Some 20 per cent of the cells began beating spontaneously about three days after being put together in vitro with cells from the hearts of rats. The cells from menstrual blood eventually formed sheet-like heart-muscle tissue.

The success rate is 100 times higher than the 0.2-0.3 per cent for stem cells taken from human bone marrow, according to Shunichiro Miyoshi, a cardiologist at Keio University's school of medicine, who is involved in the research.

Separate in-vivo experiments showed that the condition of rats who had suffered heart attacks improved after they received the cells derived from menstrual blood.

Dr Miyoshi said women may eventually be able to use their own menstrual blood.

'There may be a system in the near future that allows women to use it for their own treatment,' Dr Miyoshi said on Thursday.

The cells can be stored for a long time in a tube the size of a pinky finger and cultivated when necessary, he said.

He also said menstrual blood could be used to build stockpiles of cells which have a variety of immune types.

This could help people with matching HLAs, or human leukocyte antigens, a key part of the human immune system, he said.

'In proper storage, we would be able to stock up a tremendous count of cells in a small space. If they are not used for 100 years, they could stay there for 200 years or 300 years' waiting for a perfect match, he said.

In a strict sense, the connective cells harvested from menstrual blood cannot be called stem cells, which can turn into any type of cell in the body, Dr Miyoshi said.

But they also have high potential to develop into muscle cells, suggesting the blood could in time be used to treat muscular dystrophy, he said.

The study has been conducted jointly by researchers from private Keio University and the National Institute for Child Health and Development.

Initial results were recently published in the online edition of the US journal Stem Cell. -- AFP