Correspondence should be addressed to Dr. Li-Chen YANG, Room 103, Nanwei Road 29, Xuanwu District, Beijing, 100050. Tel: 86-10-83132906. Fax: 86-10-83132021.E-mail: Lichenjang@yahoo.com.cn;Biographical note of the first author: Li-Chen YANG, female, born in 1974, associate professor, majoring in micronutrients and health.