A Chinese herb called astragalus can boost your immune system and help you fend off infections, from the common cold to swine flu, according companies that sell it. Scientists say astragalus boosts the immune system, but it isn't known if that translates to any health benefit.

The root of a perennial called astragalus has long been used in Chinese medicine to boost the body's defenses, often with other herbs. In the U.S., it is available in teas, tinctures and as a dietary supplement.

Scientific studies, mostly in Asia, have found the herb boosts the immune system in humans, but Western studies are scant. Natural Standard Research Collaboration, a Cambridge, Mass., scientist-owned group that evaluates natural therapies, reviewed the evidence for the immune-boosting properties of astragalus and gave it a 'C' on a scale from A to F. 'A grade of C means unclear or conflicting scientific information,' says Catherine Ulbricht, senior attending pharmacist at Massachusetts General Hospital in Boston and a co-founder of Natural Standard. 'The jury is still out.'

One of the few Western studies on the immune-boosting properties of astragalus was published in 2007, using 16 human subjects. Within 24 hours, biological markers in the group that took an astragalus tincture showed the activity of white blood cells, a key part of the body's defenses against invaders, rose significantly compared with a group on a placebo.

'Certainly it does work to stimulate your immune system,' says study co-author Heather Zwickey, an immunologist at National College of Natural Medicine in Portland, Ore. But that doesn't necessarily translate into a better resistance to disease, says Dr. Zwickey, who is director of research at the college's nonprofit Helfgott Research Institute. Immune cells often target very specific pathogens, so a general boost in immune activity doesn't necessarily translate into a specific benefit, such as a better ability to fight off swine flu, she says.

The herb is inexpensive and available from a variety of makers. A concentrated version that isolates one of its component ingredients is sold by Telomerase Activation Sciences Inc. of New York. The company's formulation, called TA-65 and licensed from Geron Corp., of Menlo Park, Calif., has been shown in unpublished work to boost the immune system, says TA Sciences. The company believes its supplement works by stimulating an enzyme that lengthens telomeres, sequences at the ends of chromosomes. When telomeres get too short, cells can no longer divide; research suggests TA-65 may help lengthen telomeres on immune cells, the company says. The herb is sold as part of a package that involves extensive testing; cost is $6,725 for six months. The testing helps the company accumulate data and show clients that it is improving their health, TA Sciences says.

Astragalus isn't recommended for people with autoimmune diseases such as lupus or multiple sclerosis, where activating the immune system could be harmful. Anyone allergic to peas is likely also to be allergic to astragalus, adds Dr. Ulbricht. Like other herbs, check with your doctor before using it with other medicines.

据销售黄耆的公司称，这种中草药能够提高人体的免疫力，帮助预防从普通感冒到甲型H1N1流感在内的各种传染病。科学家们说，黄耆能够改善人体的免疫系统，但还不清楚是否能够给人体健康带来好处。

黄耆属多年生草本植物，长期以来在中药中一般都同其它草药一起用来提高人体的抵抗力。在美国，可在茶饮、药酒和膳食补充剂中见到它的踪影。

科学研究发现黄耆能够改善免疫系统，但这些研究基本上都是亚洲进行的，西方国家的相关研究很少。马萨诸塞州剑桥的天然标准研究协会（Natural Standard Research Collaboration）评估了黄耆提高免疫能力的证据，并按照从A到F的评分标准给黄耆打分为C.这个协会是一家评估天然疗法的科学家组织。天然标 准协会的创始人之一、波士顿马萨诸塞州总医院的主治药剂师乌尔布里奇（Catherine Ulbricht）说，C的评分意味着没有明确的或存在冲突性的科学信息，还没有定论。

在西方对黄耆提高免疫能力特性为数不多的研究当中，有一项2007年公布的研究，这是一个有16人参加的人体试验。在24小时内，接受黄耆酊剂的试验者与接受安慰剂的试验者相比，前者的白细胞活跃性有显着提高。白细胞是人体免疫系统的重要组成部分。

研究报告的共同作者之一、俄勒冈州波特兰美国自然医学院（National College of Natural Medicine）的免疫学家茨维奇（Heather Zwickey）说，显然黄耆确实能够刺激人的免疫系统。但她又说，这不一定就意味着黄耆能够提高人体抵御疾病的能力。茨维奇是美国自然医学院旗下非盈利 性机构赫夫戈特研究院（Helfgott Research Institute）的研究主管。她介绍说，免疫细胞通常针对的都是非常具体的病原体，因此整体提升免疫活性并不一定就能带来特定的益处，比方说提高防御 甲型H1N1流感的能力。

黄耆价格不贵，可以从很多制药商处买到。纽约制药商Telomerase Activation Sciences Inc.销售的一种药浓缩提炼出了黄耆的一种有效成分。这家公司说，研究显示，它得到加州企业Geron Corp.授权后生产的药剂TA-65可以促进免疫系统。该公司认为，这种药的功效原理是刺激一种能够延长端粒的酵素，端粒是染色体尾端的序列。TA Sciences说，当端粒太短的时候，细胞就不能再了；研究显示，TA-65能够帮助延长免疫细胞的端粒。TA-65目前被用于一种包含多种检测的 综合性治疗，6个月的治疗费用为6,725美元。TA Sciences表示，这些检测可以帮助公司积累数据，向客户显示治疗正在提高他们的健康状况。

患有红斑狼疮和多发性硬化症等自身免疫性疾病的人不建议使用黄耆；对他们而言，刺激免疫系统可能是有害的。乌尔布里奇补充说，对豌豆过敏的人群也可能会对黄耆产生过敏。与其他草药一样，在和其他药物一起使用黄耆之前需咨询医生的意见。