The effect of oral contraceptives on bone density is unclear. It might depend on dosage levels, the specific formulas, and timing. A Canadian study found that OCs resulted in lower bone density and higher risk for fractures in young women, possibly because taking OCs at younger ages interferes with achieving peak bone mass. Some evidence suggests, however, that low-dose OCs may protect against bone loss in women during the perimenopausal period. In addition, specific progestins (such as norethindrone or norgestimate) may be bone protective. More research is needed.