Surgery on ovaries is a factor. Fluoride is a negative factor. Smoking is a negative factor. Osteoporosis is not from low estrogen after menopause. Soft drinks with phosphorus pull calcium out of the bones.
Caffeine takes calcium out of the bones, as does alcohol.
Fat in the diet combines with calcium to create soaps which are unabsorbable. Sugar also takes calcium out of the bones. Milk increases the ionized calcium that is better utilized. The higher the protein, the higher should be the calcium intake. Vegetarians have less osteoporosis.