"Both NK and lumbrokinase (derived from earthworms), unlike most proteins, are more resistant to the highly acidic gastric fluids in the stomach and can be absorbed in the later sections of the digestive tract. In 1995, Fujita and colleagues demonstrated that NK could be absorbed from the rat intestinal tract in an intact form and degraded fibrinogen in plasma blood samples [3]. Subsequently, in 2013, a research team in the United States detected intact NK in the serum of healthy humans after they were administrated a single, oral dose of NK (2000 FU/100 mg) in a capsule [16]. Other studies have also shown that oral administration of NK can enhance fibrinolytic activity in plasma [3,16]. The mechanism by which NK is transported from the digestive tract into the circulatory system still needs to be elucidated. NK can resist high temperature (50 °C) and pH (to 10), which certainly contributes to the ability of this enzyme to remain intact in the gastrointestinal tract [6]."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5372539/
"Both NK and lumbrokinase (derived from earthworms), unlike most proteins, are more resistant to the highly acidic gastric fluids in the stomach and can be absorbed in the later sections of the digestive tract. In 1995, Fujita and colleagues demonstrated that NK could be absorbed from the rat intestinal tract in an intact form and degraded fibrinogen in plasma blood samples [3]. Subsequently, in 2013, a research team in the United States detected intact NK in the serum of healthy humans after they were administrated a single, oral dose of NK (2000 FU/100 mg) in a capsule [16]. Other studies have also shown that oral administration of NK can enhance fibrinolytic activity in plasma [3,16]. The mechanism by which NK is transported from the digestive tract into the circulatory system still needs to be elucidated. NK can resist high temperature (50 °C) and pH (to 10), which certainly contributes to the ability of this enzyme to remain intact in the gastrointestinal tract [6]."理化特点 编辑
https://www.ncbi.nlm.nih.gov/m/pubmed/22040882/
不止纳豆激酶，一些别的小蛋白，多数是水解蛋白酶，可以穿越肠道进入血液。蛋白只有被降解成氨基酸才能被吸收的说法过于简单化。而且纳豆激酶的片段进入血液也有生物活性。
是个孝子，很爱他的父亲，给他老父亲买了阿司匹林预防血栓。不料后来他父亲脑血管破裂，出血多，加重了病情。
一个人是否适合用阿司匹林，多听听医生的意见，不能盲目跟风。
是否服用，要仔细考虑自己的情况。
但是这纳豆属于食品，如果不是用作药物，多一点少一点估计没多大关系。没听说日本人吃纳豆吃出问题。如果要用作药物，就必须考虑剂量。
抗血栓生成的药物有两大类: 抗血小板药物及抗凝血药物。血小板聚集是产生血栓的重要起因，抗血小板药物抑制血小板聚集。除了血小板聚集这个因素之外，血栓的形成还涉及很多其它蛋白因子。抗凝血药通过作用于那些蛋白因子抑制血栓形成。
前列腺素可以转化为血栓素，血栓素促进血小板聚集，促使血栓生成。阿司匹林使环氧化酶失活，抑制前列腺素的产生，进而减少血栓素，降低血小板聚集。因此阿司匹林属于抗血小板药物。但阿司匹林对已经形成的血栓不起作用。
纳豆激酶可以降低纤维蛋白原、凝血因子VII、和凝血因VIII在血液中的水平，抑制血栓形成。属于抗凝血类。但纳豆激酶又能直接水解纤维蛋白，化解已经生成的血栓。具有对抗血栓的多重作用。
另外，纳豆激酶还有降低血压的功能。大鼠实验显示，纳豆激酶降低血压的机理与降低纤维蛋白原和血管紧张素II有关联。临睡前服用阿司匹林也可以降血压。
我最近回国旅行，当时手头没有阿司匹林，来回乘坐飞机前，服用纳豆激酶和 diosmin complex，借以降低血栓风险。
参见：
1. Nattokinase decreases plasma levels of fibrinogen, factor VII, and factor VIII in human subjects.
Hsia CH1, Shen MC, Lin JS, Wen YK, Hwang KL, Cham TM, Yang NC.
Nutr Res. 2009 Mar;29(3):190-6. doi: 10.1016/j.nutres.2009.01.009.
https://www.ncbi.nlm.nih.gov/pubmed/19358933
2. Nattokinase: An Oral Antithrombotic Agent for the Prevention of Cardiovascular Disease
Yunqi Weng,1 Jian Yao,1 Sawyer Sparks,2 and Kevin Yueju Wang2,*
Int J Mol Sci. 2017 Mar; 18(3): 523. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5372539/
3. Antihypertensive effects of continuous oral administration of nattokinase and its fragments in spontaneously hypertensive rats.
Fujita M1, Ohnishi K, Takaoka S, Ogasawara K, Fukuyama R, Nakamuta H.
Biol Pharm Bull. 2011;34(11):1696-701. https://www.ncbi.nlm.nih.gov/pubmed/22040882
4. Aspirin Administered at Bedtime, But Not on Awakening, Has an Effect on Ambulatory Blood Pressure in Hypertensive Patients
Ramón C.HermidaPhD?Diana E.AyalaMD, PhD?CarlosCalvoMD, PhD†José E.LópezMD, PhD†
Journal of the American College of Cardiology, Volume 46, Issue 6, 20 September 2005, Pages 984-985
https://www.sciencedirect.com/science/article/pii/S0735109705015603