Thursday, February 5, 2009

How Selenium Helps Protect Against Cancer

Selenium is a powerful mineral. Needed only in very small amounts, it plays a crucial role in your cells' defenses against cancer. It is a central part of the enzymes that knock out free radicals, the unstable molecules that can attack your cells and ultimately lead to cancer. It also plays a role in recycling antioxidants through the body. These antioxidants, such as vitamin E, then lower the risk of cancer by preventing free radicals from damaging cells.

Selenium may also protect the body against contaminants such as mercury, cadmium, and silver, help speed the elimination of cancer cells, and slow tumor growth.1 A selenium deficiency is very serious and can cause nerve and heart dysfunction. Fortunately, most people in the world get plenty of selenium, except, perhaps, in unusual areas where soil selenium is low and food fortification is inadequate.

Studies have shown that selenium intake above the recommended dietary allowance (RDA), while not necessary for normal body function, may protect against certain cancers. In one region of China, where epidemic rates of esophageal and gastric cancers occurred, the risk was cut in half after large dose of selenium were given.2 In populations at higher risk for prostate cancer, selenium supplements decreased risk and growth rate of tumors.3 Selenium supplements may also be able to halt the growth of polyps in the colon and reduce the risk of lung and liver cancers.4,5 However, it's still best to get your selenium from foods, because too much can be toxic.

Food Sources

The richest sources of selenium are cereals, grains, and Brazil nuts. Vegetables and fruits also provide small amounts of selenium. How much we consume is almost entirely dependent on levels of selenium in the soil where crops are grown. Fortunately, for U.S. residents and those who consume exported U.S. foods, there is generally enough in the soil to promote health. The amount of selenium needed for normal body function is only 40 micrograms per day with the RDA being 55 micrograms. Intakes of most U.S. residents easily surpass both of these values. Countries that remain at risk for selenium deficiency are China, Denmark, Finland, and New Zealand. So, if you are consuming food grown mostly in the United States, you probably don't need to worry about selenium.5

Tips for Increasing Selenium in Your Diet

While the U.S. RDA for selenium is 55 micrograms, studies show that for maximum protection against cancer, intake of selenium as high as 100 to 300 micrograms per day is necessary. To increase your intake of selenium for maximum cancer protection, base your meals on a variety of grains. For an added bonus have a serving of tofu (40 micrograms) or a single Brazil nut (120 micrograms).

References
1. Yoon SO, Kim MM, Chung AS. Inhibitory effect of selenite on invasion of ht1080 tumor cells. J Biol Chem 2001;276:20085-92.

2. Mark SD, Qiao Y, Sanford DM, et al. Prospective study of serum selenium levels and incident esophageal and gastric cancers. J Natl Cancer Inst 2000;92:1753-63.
3. Costello AJ. A randomized, controlled chemoprevention trial of selenium in familial prostate cancer: Rationale, recruitment, and design issues. Urology 2001;57(Suppl):182-4.
4. Chigbrow M, Nelson M. Inhibition of mitotic cyclin B and cdc2 kinase activity by selenomethionine in synchronized colon cancer cells. Anticancer Drugs 2001;12:43-50.
5. Combs GF Jr. Selenium in global food systems. Br J Nutr 2001;85:517-47.

硒是什么?

硒是什么?

您知道吗?目前全世界科学机构、卫生组织一致公认,毫无争议的人体必需微量元素共有八种:硒、铁、锰、铜、钴、锌、钼、碘,而其中硒(SELENCE希腊语为月亮女神)被誉为抗癌之王、心脏的守护神,对此许多中外媒体都做过报道。

那么硒是什么呢? 世界闻名营养学家,全球生物化学会主席巴博亚罗拉博士称“硒”是延长寿命最重要的矿物质营养素。它是一种珍贵稀有的矿物质营养素。它只存在于少量的天然食物中。日本科学家也指出,现在 最受到全世界注目的微量元素就是 硒。日本医学界对硒的临床研究也证实硒对癌症、糖尿病、高脂质血症、动脉硬化、皮肤不良、白内障、肾脏病、心脏病、肝病、风湿病、过敏性体质、胃溃疡、肥胖病、高血压……都具有很高的防治效果。硒是一种多功能的生命营养素。是防治功能的生命营养素。其防治疾病机理有清除自由基、抗氧化(是VE的50—100倍)、强力抑制过氧化脂质的产生、增强免疫功能(20-30倍)、保护生物细胞膜、增强前列腺调节功能、防止血凝块、清除胆固醇、具有与胰岛素相同的作用,能明显促进细胞摄取糖的能力、血液循环防止皮肤老化、降低致癌物质的诱癌性、消除体内突变的异常细胞、阻止癌细胞的分裂与生长等。

目前已知的与缺硒有关人类的疾病有40多种。包括癌症、脑心血管疾病、糖尿病、肝病、甲状腺激素失衡……等。

1996年12月24日美国权威科学机构公布经多年临床实验证实补硒能大大降低癌症的发生率及死亡率。另外,除防治癌症外,硒对防治脑血管疾病、糖尿病以及抗衰老都有很好的作用;而且硒还有些其他营养素无法具备的特殊功能,例如它能解除重金属的质癌与毒害。它还可以减轻放射线、微波对人体的伤害。 目前“硒”已成为美国人防治癌症及保健的最风行的营养素,美国医学家称硒是至今发现最强烈也最潜力的抗癌营养素。在美国,目前施行的营养剂防癌计划中,硒就是一个主角。

中国微量元素与健康学会理事长于若木指出:中国是一个缺硒大国,72%地区属于缺硒地区。天津、北京、东北都属于低硒地区。科学家更郑重呼吁:若长期低于每日50微克,就容易引起包括癌症在内的多种疾病。因此每日适量补硒能够大大降低癌症疾患,提高生命质量。

微量元素对于生命的作用要比维生素、蛋白质、氨基酸重要得多,因为后者可以在体内自行合成、制造;但微量元素却无法被制造出来。微量元素的缺乏和人类生命质量密切相关。

阮笑芬

硒缺乏的危害

硒缺乏的危害

人类硒缺乏会导致癌症、糖尿病、心脑血管疾病,已取得世界各国医学界的共识,并且确定了每4年召开一次有关硒的国际研讨会。

由于我国呈一带状的低硒地区生产的粮食含硒量极低,从而导致人体缺硒,研究发现 ,缺硒者心肌中各种成分的硒含量极低,致使心脏功能发生障碍。国外最新研究表明,低硒食物喂养的动物,心脏抗病能力减弱,容易诱发心肌类疾病。而且还认为,缺硒是冠心病的诱因。国外的资料还报道。食物中含硒越低,癌症的发生和残疾率越高。据报道, 缺 硒是引起心肌缺血, 心绞痛, 心肌梗塞的重要因秦。

在我国缺硒地区,人体缺硒影响骺板软骨变形坏死,形成大骨节,使这一地区许多入骨节变形,大骨节病患者出奇地多。通过我国医学专家于树玉历经16年的肝癌高发地区流行病学调查及大规模的人群补硒实验得到证实,肝癌的居民血液中的硒含量均低于肝癌低发区,肝癌的发生率与硒水平呈负相关。饲料中补硒使鸭子的乙肝病毒感染率及肝癌癌前病变下降77%;在江苏启东县13万居民中进行补硒预防肝癌实验证实,补硒可使肝癌发生率下降35%;使有肝癌家族史者发病率下降50%;此外还观察到补硒可增强人体免疫力,抵抗人群中病毒性肝炎的传播。

基础研究还发现,硒有调查细胞分裂、分化及癌基因表达,使癌细胞行为向正常转化的作用;动物及人的肝癌细胞株体外培养亦表明,补充硒阻断癌物的致癌作用。

我国营养学及微量元素研究专家杨光新、俆光禄教授从60年代起对缺硒地区以心肌坏死为主的克山病进行研究,对10多个省区、310个病区共900多万人进行补硒,使流行于缺硒地区克山病得到了控制。 近几年的研究还发现,在一些长寿地区,自然环境中硒含量较高,从而证实,硒有一定的预防保健及益寿的作用。

当前,人类生存环境中大气污染、农药污染、重金属及化工厂产品的有毒物质以及射线等,都会造成人体内机体环境紊乱,导致各种疾病。通过对细胞实验测定结果表明,硒有直接清除抑制人体有害物质"自由基"的作用,世界各国医学专家认为,硒是人体的"清道夫",适量补充硒有利人体健康。


阮笑芬