Low milk supply associated with menstruation: Calcium/magnesium supplement
Some women experience a drop in milk supply from ovulation (mid-cycle) until the first day or two of the next menstrual period. A woman's blood calcium levels gradually decrease during this period of time, and for some women the drop in blood calcium causes a drop in milk supply. For women who have this problem, calcium/magnesium supplements may be helpful. This practice has also been reported to eliminate most uterine cramping and some premenstrual discomfort such as water retention.
The recommended calcium supplement dosage is between 500 mg calcium/250 mg magnesium and 1500 mg calcium/750 mg magnesium (the higher dosage is generally more effective). Calcium dosages this high should not be taken alone, but as a calcium/magnesium (or calcium/magnesium/zinc) combination. Otherwise the calcium will not be adequately absorbed into your body. The amount of supplement depends on the composition of your diet -- the more animal protein, the more calcium/magnesium needed. If you are a vegetarian or vegan, the lower dosage may work fine for you.
Start the supplement when you ovulate, and continue through the first few days of your menstrual period. If periods are irregular, then begin calcium/magnesium at 14 days after the beginning of your last menstrual cycle, or simply take the supplement every day.