赵吉福 博士，天然药物化学家从事新药、化妆品及健康食品研究30余年，现居美国，任天然产物大全(www.aznpbio.com)创始人、天然产物新闻(www.usahealthresource.blogspot.com)主编。赵博士拥有药学学士、中药化学分析硕士和药物化学博士学位，哥仑比亚大学博士后。历任日本东洋医学研究所和美国肿瘤研究中心研究员、制药公司化学部主任等职。赵博士完成了数百种天然活性成分的分离、鉴定及活性研究，并用于药物、功效性化妆品或健康食品的开发，建立了来源于世界各地(北美、中南美洲、非洲、印度和欧洲等)6000多种民间药用天然产物样品库。
草酸是存在于许多植物的有机酸, 有肾毒性和腐蚀性。草酸对大鼠的半致死剂量 (LD50) 为每公斤体重375mg, 换算成一个约65kg的人，大约是25g。另外，口服的最低致死剂量 (LDLo) 约为600mg/kg 。草酸有非常刺激性的味道，长久接触草酸的水溶液，可引发关节痛。在一般人的尿液里，亦有微量草酸，大约为数毫克。草酸对混凝土、木材和玻璃均具腐蚀性。草酸盐是草酸形成的盐类, 含有草酸根离子 [C2O42-或(COO)22-], 草酸盐如: 草酸钠 (Na2C2O4), 草酸钙 (CaC2O4，肾结石的主要成分), 草酸铁钾 [K3[Fe(C2O4)3], 草酸铵[(NH4)2C2O4] 。草酸根离子属于还原性阴离子, 可被氧化剂如高锰酸钾氧化为二氧化碳。含草酸盐高的食物有菠菜、草莓、甜菜、芹菜、青椒、羊肉、土豆、核果、甜菜、核桃、巧克力等。 大豆食品含草酸盐和磷酸盐也挺高。草酸盐对粘膜具有较强的刺激作用，大量摄入草酸盐可刺激胃肠道粘膜，从而引起腹泻，甚至胃肠炎。草酸盐可被反刍动物的胃微生物降解，转化为碳酸盐和重碳酸盐, 因此反刍动物对草酸盐的耐受力较非反刍动物强。草酸盐可在血管中结晶, 并渗入血管壁, 引起血管坏死, 导致出血。草酸盐晶体可在脑内形成, 而引起中枢神经系统机能紊乱。草酸一般在人体的小肠中被吸收, 在小肠液中, 大部分草酸与游离的钙离子结合生成草酸钙结晶。被吸收入血的草酸与血液中的钙离子形成草酸钙, 它的溶解度非常低, 在肾脏中尿液被浓缩之后, 如果超过了草酸钙的溶解度, 就沉淀下来, 导致尿路结石。菠菜的草酸含量为0.97%左右。在蔬菜中, 草酸有两种存在形式，一种是结合型的不溶性草酸盐，如草酸钙；一种是易溶于水的可溶性草酸盐。有研究证明，热水焯煮能去除菠菜中50%至80%的草酸，焯煮时放的水要多一些，煮的时间长一些，焯出来的草酸就多一些。一般焯煮时间约为1分钟左右。对消化能力正常、身体健康的人来说，草酸在肠道中的吸收率并不高，而少量的草酸被吸收后一般无多大影响，甚至人体自身也会在代谢中产生少量草酸。所以，在钙摄入量充足的情况下，即便菠菜不焯水直接煮汤也没关系。只要多饮水，冲淡血液中草酸的浓度，便可防止尿路结石的发生。菠菜的草酸含量因品种、栽培方式和栽培时间有很大的不同。冬天的菠菜草酸含量低，涩味比较少，不焯也不觉得难吃。夏天的菠菜草酸多，涩味比较浓，不焯烫觉得涩嘴。菠菜和高钙食物一起吃，能够降低草酸吸收率，有利于预防肾结石。代价就是损失点钙。西方人钙摄入量高，故而不怕这种损失。Dietary oxalates are plant-derived and the component of vegetables, nuts, fruits, and grains. In normal individuals, approximately half of urinary oxalate is derived from the diet and half from endogenous synthesis. The amount of oxalate excreted in urine plays an important role in calcium oxalate stone formation. Large epidemiological cohort studies have demonstrated that urinary oxalate excretion is a continuous variable when indexed to stone risk. Thus, individuals with oxalate excretions >25 mg/day may benefit from a reduction of urinary oxalate output. To limit calcium oxalate stone growth, people should maintain appropriate hydration, avoid oxalate-rich foods, and consume an adequate amount of calcium.Hyperoxaluria occurs when you have too much oxalate in your urine. It can be caused by inherited (genetic) disorders, an intestinal disease or eating too many oxalate-rich foods. Oxalosis happens after the kidneys fail in people who have primary and intestinal causes of hyperoxaluria, and excess oxalate builds up in the blood. This can lead to oxalate deposits in blood vessels, bones and body organs. Symptoms include severe or sudden back pain, pain in the area below the ribs on the back (flank) that doesn't go away, blood in the urine, frequent urge to urinate, pain when urinating, chills or fever.Following is the list of OTC-Drugs containing herbal extracts that may cause oxalate toxicity if taking them together with oxalate-rich vegetables such as spinach:
The total and soluble oxalate contents of commonly used herbal medicines were measured:
1. Twenty-two medicinal herbs were extracted in both acid and water prior to determination of total and soluble oxalate, respectively.
2. Oxalate was assayed in herbal extracts using a well-established enzymatic procedure.
3. Results: Among the 22 medicinal herbs, there was significant variation in oxalate content; Houttuynia cordata (鱼腥草) contained the highest amount of soluble oxalate (2146 mg/100 g) and Selaginella doederleinii (卷柏) contained the lowest amount (71 mg/ 100 g).
Conclusion: The results indicated that different medicinal herbs, even from the same family, contain significantly different amounts of oxalate. In susceptible individuals, the use of medicinal herbs with the highest oxalate contents could increase risk of kidney stone formation.
Following is the oxalate content measurement result of herbs that are commonly found in OTC-Drugs:
REFERENCES:
Am J Physiol Renal Physiol. 316(3): F409–F413, 2019
Journal of Traditional Chinese Medicine, 35(5):594-599, 2015
BMC Nephrol, 13: 141, 2012
J Am Soc Nephrol 28: 876–887, 2017
Am J Respir Crit Care Med 169: 836–841, 2004
Am J Physiol Renal Physiol 300: F311–F318, 2011
J Pediatr 167: 1155–1158, 2015
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