吸烟将严重影响生育能力

2005年10月17日，首席研究员Loni Burkman博士在魁北克蒙特利尔招开的美国生殖医学学会年会中谈到：几乎有2/3的长期吸烟者的精液没能通过一项评价精液受精能力的测试。长期吸烟者的精子受精能力较不吸烟者下降了75%。

Burkman教授是UB医学和生物医学学院的男科学、妇产科生殖医学的带头人，也是泌尿外科学的助理教授。 他说：“象人体内其它细胞一样，人的精子携带有一种尼古丁受体，也就是说精子可以识别尼古丁，并对它产生反应。这是因为烟草中的尼古丁与人体内产生的一种最重要的神经化学物质相似。我们之前曾报道将尼古丁加到非吸烟者的精液中，可以改变三种受精所必需精子功能”

Burkman还说：“我们在一项新的研究中检测了长期吸烟者的精子是否存在与卵子周围的透明带结合能力下降。我们的结果显示大量吸烟使得人精子及睾丸中尼古丁受体超载，从而使得受精的能力下降。

这项研究调查了18名男性，他们均吸烟每天至少4支，烟龄至少2年，平均烟龄约为15年，并将生育能力正常的非吸烟志愿者作为对照组。

运用Burkman发明的透明带劈裂测试法（Hemizona测试法），将透明带分为两半，将其中一半与吸烟者的精子一起培养，另一半与对照组精子共培养。2~3小时后，计算与透明带紧密结合的精子数。

通过将吸烟者结合的精子数与对照组的相比得出一个比或指数的方法，Hemizona测试法可以预测体外受精时的生育缺陷。

Burkman指出：“这个指数低于65的话则不能通过这项检测，也就意味着吸烟者的生育能力低于正常志愿者的65%，而这个指数低于36的话则意味着生育能力的严重下降。”

结果显示将近2/3的吸烟者不能通过这项测试，而其它1/3吸烟者的正常。而且几乎所有不能通过这项测试的人这个指数为36或更低，平均为25。

Burkman说：“在这项研究中没有哪个的受精能力为零，但结果却意味着他们的精子仅有非吸烟者25%的受精能力。这些数据也显示与通过这项测试的人相比，未能通过者每天要吸两倍多的烟，平均为每天19支。

为了更好地理解吸烟的影响，研究者为每个吸烟者计算“吸烟负荷”，将吸烟者每天吸烟的支数乘以吸烟年数。在这18个人中“吸烟负荷”由16到750不等。

结果显示吸烟数量及时间更少的人（吸烟负荷由16到200）的人中，71%的通过了Hemizona测试，即受精功能正常。其余有更高的吸烟负荷的人中仅有18%的人通过了这个测试。

最后Burkman指示：“特殊的检测清晰地揭示了大量吸烟者生育能力的明显下降。吸烟者也应意识到吸烟还可能损害精子的DNA，甚至将错误的基因传给其下一代。关注这个问题的吸烟者应该及早戒烟或到当地的生殖实验室检查。”

Sperm from nearly two-thirds of the chronic smokers in the study failed a special test that measures the ability of sperm to fertilize an egg. On average, those men showed a 75 percent decline in fertilizing capacity when compared to nonsmokers. Lead researcher Loni Burkman, Ph.D., presented the results today (Oct. 17, 2005) at the American Society of Reproductive Medicine annual meeting in Montreal, Quebec.

Burkman is associate professor and head of the Section on Andrology, Department of Gynecology and Obstetrics in the UB School of Medicine and Biomedical Sciences and an assistant professor of urology.

"Like other cells in the body, human sperm carry a receptor for nicotine, which means they recognize and respond to nicotine," said Burkman. "This happens because nicotine from tobacco mimics one of the most important neurochemicals produced in the body. "Using sperm of nonsmokers, we reported previously that the addition of nicotine changed three sperm functions required to fertilize an egg.

"In this new study, we examined whether sperm from chronic tobacco smokers are defective in binding to the zona, the cover surrounding an egg," said Burkman. "Our results could mean that heavy smoking overloads the nicotine receptor in human sperm and in the testes, leading to a decline in fertilizing potential."

The study involved 18 men who reported smoking at least four cigarettes a day, every day, for more than two years. On average, these men had smoked for about 15 years. Their sperm function was compared to that of non-smoking donors who served as controls and whose fertilizing capacity had been confirmed.

Using a test called the Hemizona Assay developed by Burkman, the researchers cut a zona in half, placing one half with a smoker's sperm and the matching half with control sperm. After two to three hours of incubation, researchers counted the number of sperm attached tightly to the outside of each half.

The number of attached sperm from the smoker was compared to the control number, which gave a ratio or index. The Hemizona Assay has been shown to predict fertilization failure during in vitro fertilization.

"To fail, the index must be less than 65, meaning that the smoker's sperm had less than 65 percent of the fertilizing capacity found in the donor," Burkman said. "An index below 36 identifies a severe loss in fertilizing capacity."

Results showed that the sperm from almost two-thirds of the smokers failed the test, while the remainder showed normal function. Almost all the smokers whose sperm failed the test had an index of 36 or less, with an average of 25.

"None of these men had a zero fertilizing potential," said Burkman, "but the results mean that their sperm had only 25 percent of the fertilizing function found in nonsmoking men. The data also showed that the men who failed were smoking about twice as many cigarettes per day, an average of 19 per day, compared to the smokers who passed the assay."

As another way to understand the impact of smoking, the researchers calculated a "smoking load" for each smoker by multiplying the number of cigarettes smoked per day by the number of years smoked. The load varied from 16 to 750 for the 18 men.

Results showed that the men who smoked fewer cigarettes for fewer years had smaller smoking loads, ranging from 16 to 200. In this group, 71 percent passed the Hemizona Assay, indicating normal fertility. The remaining men had a high smoking load, and only 18 percent passed the assay.

"Specialized testing clearly reveals a significant drop in fertility potential for men who are heavy tobacco smokers," said Burkman. "Smoking men also should be aware that smoking can damage their sperm DNA, passing on faulty DNA to their baby. Concerned smokers should quit or be tested in a local andrology laboratory."