Starting periods after the age of 14 was associated with a 17% higher risk when compared with starting them at the age of 13, while going through the menopause below the age of 45 was associated with 46 % heightened risk compared with going through it at the age of 50-51. Hysterectomy or removal of one or both ovaries (oophorectomy) was associated with 40 per cent and 21 per cent higher risks, respectively, although only a few women had these procedures.