The report, which was put together by a team of geneticists and cited by The New York Times, used the genetic signatures of people in Spain and Portugal to prove that some 20 percent of the Iberian Peninsula's current population has Sephardic Jewish ancestry.
The results of the study also found that a high percentage of Jews during the 15th and 16th centuries converted to Islam, under the Arab Umayyad dynasty.
The research was based on an analysis of Y-chromosomes, which experts say remains the same as passed down from father to son.
Researchers examined the genetic codes of 1,140 males from the Iberian Peninsula and Balearic Islands, focusing on the distinct differences between the Y-chromosomes of north African Muslims and Sephardic Jews.
The results could not determine whether people had been forced to convert or had converted voluntarily.