Estrogen is the dominant sex hormone in females and is counterpart to testosterone, which is dominant in males. Estrogen is produced in the ovaries by the mature graffian follicle. The sex hormones are important for bone growth and strength; low estrogen is associated with weakening of bone. Calcium is the most important component of bone; a bone without calcium is very weak and prone to fracture.
Calcium Absorption
Calcium is absorbed mostly from foods that are high in calcium. Such foods include milk, cottage cheese, yogurt, soy beans and orange juice fortified with calcium. Calcium absorption takes place in the small intestine and is facilitated by vitamin D and PTH, or parathyroid hormone.
Calcium Regulation
Calcium is regulated by the thyroid and parathyroid glands, which are located in the neck. When calcium is high, the thyroid gland is stimulated to release calcitonin, a product of the thyroid para-follicular cells. When calcium is low, the parathyroid gland releases parathyroid hormone, which increases the re-absorption of calcium from kidneys and the absorption of calcium in the small intestine.
Estrogen Deficiency
Estrogen deficiency is common in women who are 50 years and older; it is referred to as menopause. Menopause is caused by failure of the ovaries to produces estrogen despite stimulation from the hypothalamus. Estrogen is responsible for growth of endometrial tissue within the uterus or the womb; a woman with low estrogen is infertile since estrogen is needed to prepare the womb for the possible implantation of a fertilized egg. Estrogen also facilitates bone mineralization and slows down the rate of bone resorption or breakdown; in menopause, there is decreased bone mineral density.
Menopause and Low Calcium
Estrogen prevents bone breakdown by inhibiting the apoptosis of osteoblasts, cells of the body that form bone with calcium. The ovarian failure in making estrogen results in a net loss of osteoblasts, thereby resulting in rapid bone density loss. Increased bone density loss can be treated by the use of bisphosphonates such as ibandronate, alendronate and zoledronic acid. Bisphosphonates are very effective in attenuating the rate of bone density loss. Vitamin D may be supplemented at 800mg per day to increase calcium absorption in the intestines.
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