The study found that up to two thirds of women carry male DNA in their brain, which was most likely passed on to them while they were pregnant with sons.
Researchers said the exact medical consequences of the transfer from foetus to mother was unclear, but it was less common in women who suffered from Alzheimer's, suggesting that it could offer protection against the condition, 'The Telegraph' reported.
Earlier studies indicate that similar processes of DNA transfer could raise the risk of some cancers, such as breast cancer, and lower the risk of others including that of colon.
The new study of brain tissue taken from 59 women who died aged 32 to 101 found male DNA in 63 per cent of specimens.
The study also showed that the male DNA was less common in the parts of the brain most severely damaged by Alzheimer's.
However, the researchers, from the Fred Hutchinson Cancer Research Centre in Seattle, emphsaised that the small scale of the study and the lack of data on the women's pregnancy history meant the evidence was not conclusive.
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"Currently, the biological significance of harbouring male DNA and male cells in the human brain requires further investigation," Dr William Chan, who led the project, said.
The findings are published in the journal 'Science ONE'.