The younger you start exercising regularly, the more bone mass you will retain. Women's death from hip fracture risk is equal to her combined risk of breast, uterine and ovarian cancer. Make sure you consume vitamin D with your calcium to aid calcium absorption. You'll need magnesium for strong bones too. Caffeine and soda can decrease your calcium level.
Caffeine increases calcium loss because it's a diuretic.
According to the National Osteoporosis Foundation, the phosphates in soda may interfere with calcium absorption. A soda with caffeine hits you from both angles. Medications which reduce bone density include steroids such as prednisone and Flovent. Hormone replacement does have side effects. Done properly, exercise has no side effects.