And he answered and said unto them,
Have ye not read,
that he which made them at the beginning made them male and female,
Matthew 19:4
"The team reviewed data on the 534 people to have flown in space at the time of the study, including 57 women, and studied cardiovascular, reproductive, musculoskeletal, immunological and behavioral health. 
Changes in zero gravity included worse vision problems among some men, calcium loss for both
sexes, and for some female astronauts, an inability to stand for long periods without fainting after landing back on earth, according to the study.
Dr. Saralyn Mark, a lead author on the study and a senior medical adviser at NASA, told ABC News that one ongoing problem for those flying in space is that the eye and even eyeball can be affected by zero gravity.
While only a small portion of astronauts were studied, 82 percent of male astronauts, or 14 out of 17, were found to have suffered from changes to their vision that researchers called visual impairment intracranial pressure, or VIIP.
They called the impairment "one of the most serious spaceflight-related health risks."
While a large majority of the male astronauts had a problem, statistically fewer women were struck with the same symptoms. Only 62 percent, or 5 out of 8 female astronauts reported the same symptoms and none had as severe symptoms as some of the male astronauts. Researchers were examining if the women’s age, hormones or vascular health helped them fare better in space.
While male astronauts battled to keep their eyesight, female astronauts have faced other difficulties back on terra firma. Female astronauts were more likely to faint while standing when they initially come back to earth, the study found.
In other cases, both men and women have faced similar problems, including “space motion sickness.” Women in space tend to report more motion sickness as they leave earth and enter the space station, whereas men report feeling queasy more often as they return to earth, the study found." ABC