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 The company's formulation, called TA-65 and licensed from Geron Corp., of Menlo Park, Calif., has been shown in unpublished work to boost the immune system, says TA Sciences.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.

    據銷售黃耆的公司稱，這種中草藥能夠提高人體的免疫力，幫助預防從普通感冒到甲型H1N1流感在內的各種傳染病。科學家們說，黃耆能夠改善人體的免疫系統，但還不清楚是否能夠給人體健康帶來好處。

    黃耆屬多年生草本植物，長期以來在中藥中一般都同其它草藥一起用來提高人體的抵抗力。在美國，可在茶飲、藥酒和膳食補充劑中見到它的蹤影。

    科學研究發現黃耆能夠改善免疫系統，但這些研究基本上都是亞洲進行的，西方國家的相關研究很少。馬薩諸塞州劍橋的天然標準研究協會（Natural Standard Research Collaboration）評估了黃耆提高免疫能力的證據，并按照從A到F的評分標準給黃耆打分為C.這個協會是一家評估天然療法的科學家組織。天然標 準協會的創始人之一、波士頓馬薩諸塞州總醫院的主治藥劑師烏爾布里奇（Catherine Ulbricht）說，C的評分意味著沒有明確的或存在沖突性的科學信息，還沒有定論。

    在西方對黃耆提高免疫能力特性為數不多的研究當中，有一項2007年公布的研究，這是一個有16人參加的人體試驗。在24小時內，接受黃耆酊劑的試驗者與接受安慰劑的試驗者相比，前者的白細胞活躍性有顯著提高。白細胞是人體免疫系統的重要組成部分。

    研究報告的共同作者之一、俄勒岡州波特蘭美國自然醫學院（National College of Natural Medicine）的免疫學家茨維奇（Heather Zwickey）說，顯然黃耆確實能夠刺激人的免疫系統。但她又說，這不一定就意味著黃耆能夠提高人體抵御疾病的能力。茨維奇是美國自然醫學院旗下非盈利 性機構赫夫戈特研究院（Helfgott Research Institute）的研究主管。她介紹說，免疫細胞通常針對的都是非常具體的病原體，因此整體提升免疫活性并不一定就能帶來特定的益處，比方說提高防御 甲型H1N1流感的能力。

    黃耆價格不貴，可以從很多制藥商處買到。紐約制藥商Telomerase Activation Sciences Inc.銷售的一種藥濃縮提煉出了黃耆的一種有效成分。這家公司說，研究顯示，它得到加州企業Geron Corp.授權后生產的藥劑TA-65可以促進免疫系統。該公司認為，這種藥的功效原理是刺激一種能夠延長端粒的酵素，端粒是染色體尾端的序列。TA Sciences說，當端粒太短的時候，細胞就不能再了；研究顯示，TA-65能夠幫助延長免疫細胞的端粒。TA-65目前被用于一種包含多種檢測的 綜合性治療，6個月的治療費用為6,725美元。TA Sciences表示，這些檢測可以幫助公司積累數據，向客戶顯示治療正在提高他們的健康狀況。

    患有紅斑狼瘡和多發性硬化癥等自身免疫性疾病的人不建議使用黃耆；對他們而言，刺激免疫系統可能是有害的。烏爾布里奇補充說，對豌豆過敏的人群也可能會對黃耆產生過敏。與其他草藥一樣，在和其他藥物一起使用黃耆之前需咨詢醫生的意見。