Oxalates and Chronic Kidney Disease: What You Need to Know

I was recently asked about the safety of collagen protein supplements and whether they could increase oxalate levels—a potential concern for people with chronic kidney disease (CKD). Since this is a big topic, I’ll cover it in a couple of posts.

Today, we’ll focus on oxalates and their role in non–stone-forming CKD. (Oxalates in kidney stone disease is a discussion for another day.)

Key reference: Oxalate Homeostasis in Non-Stone-Forming Chronic Kidney Disease: A Review of Key Findings and Perspectives

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What Are Oxalates?

Oxalates, or oxalic acid (C₂H₂O₄), are naturally occurring compounds found in many plant foods. Common high-oxalate foods include:

• Spinach
• Rhubarb
• Beet greens

Your body also produces oxalates as a normal byproduct of metabolism.

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How Does the Body Handle Oxalates?

Three main systems regulate oxalates:

• Kidneys – filter and excrete oxalates from the blood
• Intestines – excrete oxalates in stool, or use them as energy via gut bacteria

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How Does Diet Affect Oxalate Balance?

When calcium intake is adequate, about 20–40% of urinary oxalates come from diet.
When calcium intake is low, dietary oxalates can account for a much larger share.

Interestingly, diet has little impact on serum oxalic acid levels, since more than 75% of ingested oxalates are excreted within six hours.

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Which Amino Acids Contribute to Oxalate Production?

Around 40% of oxalates are produced from amino acid metabolism, specifically:

• Glycine
• Hydroxyproline
• Hydroxylysine

These amino acids form glyoxylate, which the liver converts—along with vitamin C—into oxalates.

Some people have genetic mutations that impair oxalate metabolism, leading to primary hyperoxaluria. (Read more here: Should Adults on HD With Oxalate Nephropathy Follow a Low-Oxalate Diet Before Transplant?)

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Factors That Impact Oxalate Absorption in the Gut

Several factors influence how much oxalate your body absorbs:

• Dietary fiber – high intake lowers absorption; low intake raises it
• Calcium intake – binds oxalates and increases fecal excretion
• Gut motility
• Antibiotics – alter gut bacteria that normally use oxalates for energy
• Medications – e.g., PPIs increase intestinal permeability and oxalate absorption

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Can Oxalates Affect Other Nutrients?

Yes. Oxalates are considered an anti-nutrient because they can reduce absorption of key minerals:

• Calcium
• Magnesium
• Zinc
• Iron

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Does Vitamin D Status Matter?

Vitamin D deficiency may raise parathyroid hormone (PTH) levels. This can lead to hypercalcemia and hypercalciuria, which in turn may increase the risk of hyperoxaluria.

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Are Oxalates Linked to CKD Progression?

Research suggests oxalates may play a role in non-stone-forming CKD progression, though mechanisms are not fully understood. Proposed effects include:

• Increasing inflammation, fibrosis, and cell injury in kidney tissue
• Contributing to low-grade systemic inflammation
• Disrupting the gut–kidney axis

Acidic urine is linked with higher oxalate and protein excretion, which could also contribute to CKD Progression. Additionally, Oxalates have also been linked to higher risks of CKD complications, including cardiovascular disease.

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Should People With CKD Follow a Low-Oxalate Diet?

Currently, there’s no clear evidence that a low-oxalate diet slows CKD progression.

Only one large prospective study has shown a link between higher oxalate intake and increased risk of hypertension and CKD—especially when calcium intake was low.

Bottom line: We don’t yet know if lowering oxalates will protect kidney function.

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So What Should We Recommend to Help Manage Oxalates in CKD?

Even though we don’t know if a low-oxalate diet improves outcomes, several strategies may help:

• Ensure adequate calcium intake
• Maintain good fluid intake (unless restricted for medical reasons)
• Engage in regular exercise

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Are There Supplements That Can Help?

This is still an active area of research. The four highlighted in the article were:

• Calcium supplements (calcium acetate or calcium carbonate): Used in CKD as phosphate binders, they can also reduce urinary oxalate. But balance is key—too much calcium may increase the risk of vascular calcification. Aim for a total calcium intake of ~1000 mg/day.
• Magnesium supplements (especially magnesium citrate): Magnesium binds oxalates in the gut and reduces absorption. More studies are needed to determine optimal dosing and long-term effects.
• Vitamin B6: Currently, there’s no strong evidence that B6 prevents hyperoxaluria or hyperoxalemia.
• Vitamin D: Similarly, evidence is lacking to support its role in preventing oxalate-related complications.

Key Takeaways

• Oxalates are naturally found in plant foods and produced by the body as part of normal metabolism.
• Calcium intake strongly influences oxalate absorption—adequate calcium reduces oxalate load.
• Factors like fiber intake, gut health, antibiotics, and PPIs can increase oxalate absorption.
• Evidence suggests oxalates could contribute to CKD progression and complications, but mechanisms are not fully understood.
• At present, there’s no clear proof that a low-oxalate diet prevents CKD progression.
• Helpful strategies include: ensuring adequate calcium, maintaining hydration, and exercising regularly.
• Supplements under study include calcium, magnesium, vitamin B6, and vitamin D—but evidence is limited.