This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Smoking has which effect on Uterine leiomyoma formation 
Select and explain. 
A. Higher risk of fibroid uterus, B. Lowers risk of leiomyoma formation, C. No change compared to general population, D. Higher risk of fibroid uterus in postmenopausal women
B: Lowers risk of leiomyoma formation
Answer: B: Lowers risk of leiomyoma formation 
Explanation: Smoking alters estrogen metabolism and lowers physiologically active serum estrogen levels. This explains lower risk of leiomyoma formation in smokers.