Smoking leads to an increased risk for osteoporosis (among other things, such as lung cancer). For starters, the tobacco in cigarettes decreases bone density because it adversely affects your bone cells. The more cigarettes you use in your lifetime, the higher your fracture risk when you're older (past 65).

Women, who are already very vulnerable to osteoporosis, should avoid smoking because it can limit how much estrogen you produce. From a bone health standpoint, that's bad for two reasons: first of all, estrogen helps protect your bones, and secondly, the effect of smoking on your estrogen levels may put you into menopause earlier than non-smokers—another potential risk factor for osteoporosis.