A woman's period may be shortened by various chemical or behavioral factors, according to The Access Project and WebMD. Chemical factors consist of substances that effect hormone levels, such as the ones in birth control pills or different plants, while behavioral factors include exercise, sexual intercourse and drinking enough water.
WebMD mentions that the fertility cycle is greatly affected by the level of hormones such as estrogen and progesterone, so it may be shortened by chemicals that effect these hormones. Behavioral methods of reducing the duration of menstruation are daily physical exercises and activities that induce orgasm, such as sexual intercourse or masturbation, which stimulate the discharge of the lining inside the uterus. Finally, the Mayo Clinic reports that the menstrual cycle tends to become shorter with aging.