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Oxalic Acid and Oxalates: Health Effects and Kidney Stones

Linda Crampton is a writer and teacher with a first-class honors degree in biology. She often writes about the scientific basis of disease.

A healthy salad; the beets are high in oxalate, however

A healthy salad; the beets are high in oxalate, however

What Is Oxalic Acid?

Oxalic acid is a colorless, crystalline substance that is poisonous to humans in its pure form or when it’s dissolved in a liquid to make a concentrated solution. Potentially dangerous levels of the chemical are found in products such as certain wood cleaners, metal cleaners, rust treatments, bleaches, disinfectants, and pesticides.

Oxalic acid is also found in many plants, but at much lower concentrations than in synthetic products. Most of these plants are safe for human consumption and are healthy foods. Some contain enough oxalic acid (generally in the form of oxalate) to cause health problems in sensitive people, however. The best known of these problems is the production of calcium oxalate kidney stones.

A model of an oxalic acid molecule: the black balls represent carbon atoms, the red ones represent oxygen atoms, and the white ones represent hydrogen atoms

A model of an oxalic acid molecule: the black balls represent carbon atoms, the red ones represent oxygen atoms, and the white ones represent hydrogen atoms

What Are Oxalates?

Oxalic acid often exists as oxalate in plants. When an oxalic acid molecule loses its two hydrogen atoms, it forms an oxalate ion. Oxalate ions join with certain metal ions to form salts, such as calcium oxalate and magnesium oxalate.

Calcium oxalate has very low solubility in water and tends to form crystals instead of dissolving. In some people, these crystals form stones in the kidneys. People at risk for forming the kidney stones are often advised to follow a low oxalate diet.

This is a nutritious and delicious salad, but the spinach contains oxalates.

This is a nutritious and delicious salad, but the spinach contains oxalates.

Oxalic Acid Poisoning From Commercial Products

Oxalic acid is also known as ethanedioic acid. It can be useful in commercial products, but it must be treated with care. Oxalic acid cleaners are used to remove rust, paint, varnish, and ink stains from surfaces. They are also used as disinfectants to clean toilets and as pesticides to kill varroa mites in beehives. The acid is an important reactant in certain chemical reactions and is used in some industries and chemistry laboratories.

Synthetic oxalic acid products are more likely to be poisonous than oxalic acid in plants. The concentrated acid is corrosive and can burn the skin and eyes, irritate the lungs, and make breathing difficult. It can also cause a headache, nausea, vomiting, dizziness, and convulsions. In addition, it can lower the calcium level in the body and cause kidney damage. The acid enters our bodies by ingestion, inhalation, and skin absorption.

It's very important to use oxalic acid and products containing it with great care, using all the safety precautions listed on the product label. The products should be kept in a secure location so that children and pets can't get to them. It's a good idea to use a less toxic substance if this is possible.

Cocoa is high in oxalate.

Cocoa is high in oxalate.

Oxalates in Plants

Plants are healthy foods and according to dietitians and nutritionists should form a large part of our diet. A lot of plants contain a significant amount of oxalic acid or oxalates, however. This isn't a problem for many people, but for others the chemicals may cause health problems.

An example of a plant containing a large amount of oxalic acid is rhubarb. Rhubarb stalks make a nice meal when cooked and sweetened. Rhubarb leaves shouldn't be eaten, however. They are so rich in oxalic acid that they are considered to be poisonous for everyone, whether or not they are sensitive to the chemical.

Determining accurate oxalate levels in plants is hard, as described below. This is why the lists of low oxalate foods from different sources vary. In general, though, plant foods that are considered to be high in oxalates include:

  • sorrel
  • beets
  • leeks
  • spinach
  • Swiss chard
  • okra
  • sweet potatoes
  • tea
  • cocoa
  • certain legumes or pulses, including soybeans and peanuts
  • some nuts
  • seeds
  • berries

More detailed lists are given in the links at the end of this article. As noted below, however, although the links go to health and medical sources, a health professional should be consulted in person before a low oxalate diet is started. A person shouldn't start the diet without professional advice due to the danger of avoiding nutritious foods unnecessarily and of not eating suitable substitutes for the eliminated foods.

Rhubarb stalks make a nice dessert when sweetened, but the leaves of the plant are very high in oxalic acid and shouldn't be eaten.

Rhubarb stalks make a nice dessert when sweetened, but the leaves of the plant are very high in oxalic acid and shouldn't be eaten.

Determining the Amount of Oxalic Acid in Plants

Determining the amount of oxalate provided by a particular plant is quite difficult. It depends on variable conditions such as the environment in which the plant was grown, the age of the plant when it was harvested, and the way in which the plant is prepared for eating. The serving size is important, too.

In addition, the form of the oxalate in the plant is significant. The more soluble types, such as magnesium oxalate, may be absorbed into the body from the small intestine, while the less soluble ones, such as calcium oxalate, may stay in the intestine and be passed harmlessly out of the body. Foods from animals don't contain as much oxalate as foods from plants.

Oxalates in the Diet and Nutrient Absorption

There are some concerns that eating plants rich in oxalates can decrease our mineral intake. For example, spinach is a healthy food and contains a lot of iron and some calcium too, but it’s also high in oxalate. The chemical binds to both iron and calcium, preventing the substances from being absorbed from our small intestine.

Some researchers say that provided we eat a wide variety of food and don't eat a huge amount of food that is rich in oxalates, we don't need to worry about a lower intake of nutrients. Spinach and many other plants are great additions to the diet for most of us.

In the urinary system diagram above, 2 = kidney, 3 = renal pelvis, 4 = ureter, 5 = urinary bladder and 6 = urethra. The other numbers represent nearby structures and blood vessels.

Calcium Oxalate Kidney Stones

The kidneys extract waste and excess water from blood to make urine. The urine is sent to the urinary bladder through tubes called ureters. When the bladder is full, urine is released from the body through the urethra.

About 80% of kidney stones are made of calcium oxalate. A kidney stone often causes no pain if it remains in the kidney. If it's very small, it may pass through a ureter and out of the body without difficulty. A larger stone trying to pass through a ureter may cause severe pain, however.

A stone can be removed by a variety of medical treatments. Once a person has experienced one kidney stone, the chance of developing another one is increased.

Urine is produced inside the kidney. It eventually drains into a tube called the ureter, which transports the urine to the urinary bladder. Stones generally form in the kidney but may enter or be produced in the ureter, as shown in the illustration above. Stones may also be produced in the urinary bladder.

Diet and Kidney Stones

In some people, there is a genetic basis for the tendency to develop kidney stones and the stones run in the family. This isn't always true, however. Diet plays an important role in the creation or prevention of a calcium oxalate kidney stone in people who are sensitive to oxalates.

  • Dehydration increases the risk of kidney stone development, since it causes a concentrated urine to be produced. In a person who is well hydrated, water dilutes the calcium oxalate in the urine and make the development of a kidney stone less likely.
  • A diet that is high in oxalates may increase the risk of kidney stones, since it increases the probability that the chemicals will be excreted into the urine.
  • A diet high in salt promotes kidney stone formation by causing calcium to enter the urine. The calcium then binds with oxalate in the urine, potentially leading to the production of a stone.
  • We make oxalate in our bodies. Researchers have discovered that taking high doses of vitamin C supplements increases our production of the chemical.
  • Eating a lot of animal protein reduces the amount of citrate in the urine. Citrates and citric acid are inhibitors of kidney stone development. Citrate binds to calcium in the urine, preventing it from binding to oxalate. Doctors may prescribe citrate supplements to their patients who have a tendency to develop kidney stones.

Anyone with kidney stones, with symptoms suggesting the presence of a stone, or who is at risk for stone development should seek a doctor's advice.

Calcium in the Diet

Interestingly, doctors often say that patients who are susceptible to calcium oxalate kidney stones don't need to follow a diet that's low in calcium. Calcium in the body isn't a problem, as long as it doesn't collect in urine containing a high level of oxalate. In fact, calcium in food seems to be helpful to people who tend to develop kidney stones.

Some researchers recommend that calcium supplements be avoided or be taken with a meal. Some of the calcium binds with oxalate in food, forming insoluble calcium oxalate and preventing the oxalate from being absorbed from the digestive tract. The use of calcium supplements by someone susceptible to kidney stones should be discussed with a doctor.

Remember that if you form kidney stones made from a substance other than calcium oxalate, the dietary steps to prevent stone formation will be different. A doctor's advice should be sought when dealing with any type of kidney stones. Drinking a sufficient quantity of water and reducing salt intake are good steps for everyone to follow, though.

A Kidney Stone Poll

References

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2012 Linda Crampton

Comments

Linda Crampton (author) from British Columbia, Canada on November 21, 2014:

Hi, emmy. As far as researchers know, oxalate has no function in the body. It's just a by-product of chemical reactions in our body and must be excreted.

emmy on November 21, 2014:

oxalate is harmful for body so why our body makes it from vitamin c or other compounds?? i mean is there any beneficial effect of this oxalate

Linda Crampton (author) from British Columbia, Canada on June 19, 2012:

Thank you very much for the comment, toomuchmint. Your salad sounds delicious!

toomuchmint on June 19, 2012:

Great informative hub! I eat dandelion, clover and plantain from my yard. I used to eat sorrel, too but someone warned me that it was high in oxalic acid. I was pretty sure the oxalic acid wasn't harmful (I'm not sensitive), but I've been wary of it since.

I think I'll celebrate this new information with a sorrel-clover-dandelion salad. Thanks!

Linda Crampton (author) from British Columbia, Canada on June 07, 2012:

Hi, DanaTeresa. Thank you very much for the comment and the vote.

Linda Crampton (author) from British Columbia, Canada on June 07, 2012:

Thank you for the visit and the comment, snowdrops!

Dana Strang from Ohio on June 07, 2012:

very interesting information. i am impressed by the level of detail, yet it was still enjoyable to read. voted up and interesting.

snowdrops from The Second Star to the Right on June 07, 2012:

This is very interesting! Great write!

Linda Crampton (author) from British Columbia, Canada on June 05, 2012:

Hi, Tina. Thank you very much for the comment, the vote and the share! It is good to be aware of the problem, especially since the incidence of kidney stones is increasing in some countries.

Christina Lornemark from Sweden on June 05, 2012:

Very interesting article as always in your corner and I learned many new things. I knew about rhubarb and Oxalic acid but not so much about the other things to avoid. This a fabulous hub with good content and so well designed. I have never had any problem with kidney stones but one just never know and it is better to be informed. Voted up, interesting and shared!

Tina

Linda Crampton (author) from British Columbia, Canada on June 05, 2012:

Thank you so much for the wonderful comment, Sharyn!! I appreciate your comment and the share very much! Good luck with your diet - I hope you avoid another kidney stone.

Sharon Smith from Northeast Ohio USA on June 05, 2012:

Alicia ~ I must say I am totally impressed with this hub. Awesome research and information. The photo, the poll, the video, the links, are all great too. Just a few weeks ago, my doc had me go see a dietician. I have been having problems with my kidneys and have a history of kidney stones. Tests have shown high oxalate. So I went to "get a low oxalate diet." Well crap, I wish I just had your hub here. It is WAY better than any information I have received from the medical specialists. Thank you so much! I am bookmarking so I can refer to the article and the food chart too. I am also sharing this great work.

Sharyn

Linda Crampton (author) from British Columbia, Canada on June 05, 2012:

Thank you for the vote and the share, Nell! Your reaction to cleaning liquids sounds very scary. It may not be oxalic acid that you're responding to, but in any case your plan to use natural cleaning products sounds like an excellent idea! I wouldn't worry about vitamin C supplements, provided they're taken in a moderate dose. Deciding what supplements to take and in what dose is a difficult job, though!

Linda Crampton (author) from British Columbia, Canada on June 05, 2012:

Thank you, Peggy. I appreciate the comment, the vote and the share! By a strange coincidence, two days after I published this hub I was talking to a student of mine and discovered that her mother had just gone through a very painful time with a kidney stone. I'm going to keep drinking lots of water myself, just in case!

Nell Rose from England on June 05, 2012:

Hi, thats a good idea to take the calcium to stop it collecting in the body, I remember reading about rhubarb leaves being poisonous but didn't realise why. It does make sense though when you mention the cleaning stuff, I am absolutely terrible with anything like varnish or remover, and even oven cleaning liquids, my body starts to shake, I feel as though I am going to pass out and I can't breath, now I know why! thanks for this informative hub, I am definitely sticking to my natural cleaning products from now on, and the vitamin c? Wow! I take them all the time! voted up and shared, nell

Peggy Woods from Houston, Texas on June 05, 2012:

Hi Alicia,

Fortunately I have never had a kidney stone...at least one of which I was aware. I do drink lots of water. I also love spinach and other foods that contain oxalic acid. Very informative hub! Up votes and SHARING so that other people can become informed. Good work!

Linda Crampton (author) from British Columbia, Canada on June 04, 2012:

Thank you very much for the comment and the share, denisemai! I appreciate them both.

Denise Mai from Idaho on June 04, 2012:

I've always wondered what causes kidney stones. This is very useful. Well done!I'm sharing this with my followers.

Linda Crampton (author) from British Columbia, Canada on June 04, 2012:

Thank you for another lovely comment, drbj. I appreciate your visits very much!

drbj and sherry from south Florida on June 04, 2012:

As usual, Alicia, fascinating information about oxalates and oxalic acid that may also be very helpful to people at risk for kidney stones. Thank you for your excellent research and documentation.

Linda Crampton (author) from British Columbia, Canada on June 03, 2012:

Thanks for the visit and the comment, rahul0324.

Jessee R from Gurgaon, India on June 03, 2012:

Very useful and very interesting... I found the hub very useful

Linda Crampton (author) from British Columbia, Canada on June 03, 2012:

Thank you for the comment, mary. I enjoy creating salads!

Mary Hyatt from Florida on June 03, 2012:

Many thanks! BTW: that salad makes my mouth water!

Linda Crampton (author) from British Columbia, Canada on June 03, 2012:

Hi, Mary. I'm sorry that you actually lost a kidney because of a stone! I'm going to read your hub on the topic right now - and yes, you may certainly link this hub to your hub. I appreciate the link and the votes!

Linda Crampton (author) from British Columbia, Canada on June 03, 2012:

Thanks for the visit and the comment, Tom. I appreciate the votes, too!

Mary Hyatt from Florida on June 03, 2012:

Very good article on kidney stones. I lost a kidney due to a large stone that actually took over the the kidney. I drink lots of water to protect my one kidney now. When you have time read my Hub about losing a kidney. May I link this Hub into that one I wrote? Thanks in advance. I voted this Hub UP, etc.

Linda Crampton (author) from British Columbia, Canada on June 03, 2012:

Hi, Joyce. That's the interesting thing about oxalates - some people are sensitive to them and some people aren't, and researchers aren't always clear why! The only people who should follow a low-oxalate diet are those who have already produced a kidney stone that has been proven to be made of calcium oxalate, and perhaps people with other disorders in which sensitivity to oxalates is a suspected - but not a proven - cause. The rest of us don't need to worry about oxalates and oxalic acid in food (except for the oxalic acid in rhubarb leaves)! Thanks for commenting and for the votes.

Thomas Silvia from Massachusetts on June 03, 2012:

Thanks for all this great and well written information, i learned something new today !

Vote up and more !!!

Joyce Haragsim from Southern Nevada on June 03, 2012:

I grew up eating home grown rhubarb and no kidney stones for me. We eat a lot of spinch and dark green vegetables, which are supposed to be the best.

So what is that panic about?

Voted useful and interesting, Joyce.

Linda Crampton (author) from British Columbia, Canada on June 02, 2012:

Thank you, Augustine! Kidney stones can be extremely painful - I'm glad that you've managed to go for twenty years without getting another one!

Augustine A Zavala from Texas on June 02, 2012:

Outstanding article! I had a kidney stone about twenty years ago, and do what I can to prevent recurrence. Thank you for sharing.