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Calcium Oxalate: Properties, Sources, Prevention

Sep 2, 2022

You have heard about kidney stones. Do you know what they are? Kidney stones are hard bunches of minerals and other matter that form in the kidneys. These contain a chemical compound called oxalate. The main cause of kidney stones is some green leafy vegetables combined with calcium.

Do you know about the cause of kidney stones? What food items increase the chances of kidney stones in your body? They are caused due to excess calcium oxalate in the body. In this article, you will know more about calcium oxalate dihydrate crystals, their sources, and their causes.


What Is Calcium Oxalate?

Calcium oxalate is simply the calcium salts of oxalic acid. It has the molecular formula CaC₂O₄. The other name given to calcium oxalate is oxalate of lime. It generally occurs in the hydrated form. It is a colourless compound whether found in anhydrous form or hydrated form.

It is also found naturally in many plants. Calcium oxalate accumulation is linked to the plant’s detoxification of calcium (Ca²⁺). Upon decomposition, it is oxidised by fungi, bacteria, or wildfire and produces soil nutrient calcium carbonate (CaCO₃).


Some plants contain an excess amount of calcium oxalate. If such plants are consumed, it may result in uncomfortable symptoms. Insoluble calcium oxalate crystals are found in plant roots, stems, and leaves.

Properties of Calcium Oxalate

Calcium oxalate is also known as calcium salt of ethanedionic acid or calcium salt of oxalic acid. It shows various physical and chemical properties. Some of them are

  • The molecular or chemical formula of calcium oxalate is CaC₂O₄.
  • Calcium oxalate has 128.096 g/mol as its molar mass.
  • It appears colourless or white crystal, whether in anhydrous or hydrated form.
  • The density of monohydrate calcium oxalate is 2.20 g/cm³.
  • Its melting point is 200°C. It means the monohydrate form of calcium oxalate starts decomposing at this temperature.
  • It is highly insoluble in water.
  • Due to the basicity of oxalate ions, it is basic in aqueous solutions.
  • Due to its lower solubility than sodium oxalate, its basicity is lower than sodium salt of oxalic acid.
  • It is a coordination polymer in which oxalate ions are in a planar geometry. The whole molecule is ligated with water ligands.

What Are Calcium Oxalate Dihydrate Crystals?

When the amount of oxalate in the body reaches a very high level or you are facing a problem with urine, i.e., there is an issue of too little urine, it may lead to the calcium oxalate present in your body crystallising and forming clusters.

As a result, these clusters of calcium oxalate become stones in your kidney. They can be very painful and can cause complications in your body. Even the most general cause of kidney stones is calcium oxalate dihydrate crystals.


What Are the Sources of the Formation of Calcium Oxalate Dihydrate Crystals in the Body?

There are many calcium oxalate foods, as many plants contain oxalate. So, it is hard to avoid them entirely. Some food is rich in oxalate, while some have a low amount of calcium oxalate.

Some high calcium oxalate foods:

OkraWheat branGrits
Miso soupNavy beansBaked potatoes with skin
BeetsChocolateFrench fries
Nuts and SeedsSoy ProductsStrawberries
RaspberriesTeaSweet Potatoes
Stevia sweetenersAlmondsSwiss chard

Some other calcium oxalate foods that can cause kidney stones are

  • Salt
  • Animal protein
  • Vitamin C
  • Sesame seeds
  • Green leafy vegetable

What Does Calcium Oxalate in Urine Indicate?

Although excess calcium oxalate in the body gives rise to kidney stones, it is not confirmed in every case. The kidneys appropriately remove calcium oxalate. Stone formation occurs when there is sufficient concentration to make it come out of solution and build upon itself or another nidus in the kidney, perhaps a crystal of uric acid, calcium carbonate, or calcium phosphate.

Some symptoms of calcium oxalate in urine are

  • pain when you urinate
  • pain in your back and side that can come in waves or intense
  • cloudy urine
  • blood in your urine, which can look pink, red, or brown
  • constant and an urgent need to urinate
  • foul-smelling urine
  • feel chills and fever if you suffer an infection
  • vomiting and nausea

What Are the Causes of the Formation of Calcium Oxalate?

Urine contains certain chemicals that usually prevent oxalate molecules from binding together, and as a result, crystals do not form. However, if you have too much oxalate or too little urine, it may crystallise and form stones. Causes of these are:

  • Lack of fluid absorption, i.e., being dehydrated.
  • Including a lot of oxalates, salt, or protein in your diet.

In other cases, a fundamental disease causes the crystals to form stones. 


Calcium oxalate stones are the most fundamental among others. 

They are only because of

  • Having too much parathyroid hormone or hyperparathyroidism.
  • Suffering from IBD (Inflammatory Bowel Diseases), such as Crohn’s disease or ulcerative colitis.
  • Having an inherited disorder that damages the kidneys, i.e., Dent disease.
  • Obesity.
  • Diabetes.
  • Gastric bypass surgery for weight loss.

How Are Calcium Oxalate Stones Diagnosed?

Normally, the following tests are prescribed by the doctors to verify the presence of calcium oxalate stones in the body:

  • Blood test: A blood test helps with gene mutation. It aids in knowing the cause of Dent disease. Doctors usually prescribe a blood test to know better results.
  • Urine test: It is also requested to take a 24-hour urine sample. By examining your urine sample, doctors verify the oxalate levels in your urine. Generally, the oxalate level in normal urine is less than 45 mg/day.
  • Imaging tests: A CT scan or X-ray shows the location of stones in your kidney. It assists a doctor in operating them properly.

How to Prevent Calcium Oxalate Crystals?

The following tips or steps can aid you in preventing calcium oxalate crystals from forming in your kidney or your urine.

  • Limit your salt intake: A high-sodium diet can increase the amount of calcium in your urine, which can assist in stone formation.
  • Increase liquid intake: Drinking 2.5 litres of water every day is usually suggested by doctors for people to avoid kidney stone issues. The right intake of a liquid diet is necessary.
  • Maintain your calcium absorption through diet: Reducing calcium absorption in your diet can increase the amount of oxalate in the body. This imbalance will cause stone problems. So, it is best to turn to a nutritionist and get an appropriate calcium intake chart. Generally, food like milk, cheese, and milk products are suggested as these are rich in calcium.
  • Avoid high oxalate-containing food items: If you are eating high oxalate-containing food items, try to take them with calcium-containing items, such as a glass of milk. This way, oxalate from your diet binds with calcium before reaching the kidney. As a result, it would not crystallise in your urine and cause kidney stones.
  • Have a look at your protein ingestion: Protein is also known as a body-building food. It is a vital component of maintaining health and body tissues. However, the over-ingestion of protein also leads to many diseases. Too much intake of protein can result in the formation of stones in your kidney. Do not let your protein intake exceed 30% of your total daily calories as a daily requirement.

Point To Remember

If you doubt having calcium oxalate stones in your kidney or have stones symptoms, visit your doctor or a urologist. Ask for their suggestions and best treatment plans. Consult your diet plans to prevent these stones in future again.


Oxalates are found in many food items, and it is hard to avoid them from eating. But, the formation of calcium oxalate in the body can cause many complications such as urinary tract infections, kidney stones, etc. However, taking certain dietary changes can aid you in preventing them.

Various types of kidney stones depend on the mineral they combine. Calcium oxalate stones are the most common among them. You can visit your healthcare providers if you suffer from any of the symptoms mentioned above. They can test your stone, identify the type, and recommend your treatment accordingly.

Frequently Asked Questions

1) How can intake of high salt cause kidney stones?

 A) The high salt intake increases the amount of sodium in the body. It ultimately raises the amount of calcium in the urine. Once you finish eating, the oxalate from food items reacts with this calcium in the kidney. Then it forms calcium oxalate. This calcium oxalate in urine indicates the presence of kidney stones.

So limit canned foods, fast foods, packaged meats, and condiments in your diet.

2) What is the procedure for forming calcium oxalate dihydrate crystals in the body?

 A) When you eat oxalate-rich food items, your gastrointestinal tract breaks them and absorbs nutrients. The remaining waste travels from the gastrointestinal to your kidneys. From there, the waste is removed from your urine. This waste is in the form of oxalates. It combines with calcium and forms calcium oxalate dihydrate crystals in the urine.

3) What is the function of calcium oxalate crystals in plants?

A) Calcium oxalate is a general biomineral present in plants. It occurs in the form of various shaped crystals. In plants, it is found in any tissue or organ. Calcium oxalate crystal formation in plants appears to play a central role in a variety of vital functions, including

  • tissue calcium regulation
  • protection from herbivory
  • metal detoxification


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