<prompt> Smoking has which effect on Uterine leiomyoma formationHigher risk of fibroid uterusLowers risk of leiomyoma formationNo change compared to general populationHigher risk of fibroid uterus in postmenopausal women  <response>: Smoking alters estrogen metabolism and lowers physiologically active serum estrogen levels. This explains lower risk of leiomyoma formation in smokers. 