Researchers at Seoul National University Bundang Hosptial (SNUBH) have discovered that childbirth and abortion can affects the risk of Alzheimer's disease in women, the hospital said Monday.

Women have a higher risk of developing Alzheimer's than men and have more severe symptoms. Such increased risk is known to be the cause of rapid change in sex hormone experienced during pregnancy, childbirth and abortion. Until now, however, there have been no significant researches to back the theory.

The team, led by Professor Kim Ki-woong of the department of neuropsychiatry at the hospital, examined 3,574 women aged 60 years or older in Korea to see how their experience of birth and heritage affects the risk of Alzheimer's diseases.

The team also cooperated with a Greek research team and added 1,074 Greek women aged 65 years and older to include Western data.

As a result, women who had more than five births had a 70 percent higher risk of suffering from Alzheimer’s disease than women who had one to four births. Also, women who have experienced abortions were found to have half the risk of Alzheimer's disease compared to women who did not, which came as a surprise for the related community. The effects of birth and abortion on the risk of Alzheimer's disease were similar for Korean and Greek women.

The team also conducted a mini-mental state examination (MMSE) to investigate if childbirth and abortion can affect the cognitive abilities of women who do not have dementia.

The data showed that even if the women do not develop dementia, those who give more than five births experience the decrease of cognitive function, while the experience of abortion increases cognitive function.

“The estrogen level in a woman’s blood, which is known to protect the nerves, gradually increases to 40 times before pregnancy and return to pre-pregnancy levels within days after birth,” Professor Kim said. “However, the team’s studies have shown that excessively high levels or a sudden decrease in estrogen can cause neurotoxicity.”

Moreover, repeated experiencing such rapid hormonal changes with multiple births can adversely affect cognitive function, Kim added.

The journal Neurology published the results of the study.