Volume of Menstrual Blood Loss

Menstrual blood loss occurs in many primates, including humans and apes. The volume of blood lost varies substantially across species. Normal human females lose approximately 80 ml of fluid per menstrual cycle, with blood comprising about half of that volume. This volume is significantly greater in humans than in gorillas and orangutans. Anecdotal evidence suggests the human volume is also greater that of chimpanzees, although these claims have not been specifically quantified. The volume of blood lost through human menstruation is thought to underlie the high rate of iron deficiency found in women. It has also been suggested to cause significant predator risk. A number of speculative theories have been put forward to explain the reasons for the high volume of human menstrual blood loss, including that it provides protection from pathogens in semen, that it is an incidental result of characteristics of endometrial vasculature or the hemochorial placenta, that it is caused by the relatively large size of the human uterus, that it reduces the energy cost of endometrial regression, or that it defends against uterine neoplasm. Many human societies have strong menstrual taboos, regulating the activities of menstruating women.