Calcium Prevent Menstrual Cramps

Dysmenorrhea, or painful menstruation, is classified as either primary or secondary. Primary dysmenorrhea generally occurs within a couple of years of the first menstrual period. The pain tends to decrease with age and very often resolves after childbirth. Secondary dysmenorrhea is commonly a result of endometriosis, starts later in life, and tends to increase in intensity over time.
As many as half of menstruating women are affected by dysmenorrhea, and of these about 10% have severe dysmenorrhea, which greatly limits activities for one to three days each month.

Calcium may help prevent menstrual cramps by maintaining normal muscle tone. Muscles that are calcium-deficient tend to be hyperactive and therefore more likely to cramp. Calcium has been reported to reduce pain during the menstrual phase of the cycle and reduce water retention during the premenstrual phase.5 Calcium supplementation of 1,000 mg per day can be taken throughout the month. During acute menstrual cramps, calcium can be taken in the amount of 250–500 mg every four hours for pain relief, up to a total of 2,000 mg per day.

References:
Galeao R. La dysmenorrhee, syndrome multiforme. Gynecologie 1974;25:125

Penland J, Johnson P. Dietary calcium and manganese effects on menstrual cycle symptoms. Am J Obstet Gynecol 1993;168:1417–23.