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BUN

Kidney Unit: mg/dL

Kidney filtration marker

Also known as: Blood Urea Nitrogen,Urea Nitrogen

Reference Ranges

Clinical Reference 7.0 – 20.0 mg/dL
Optimal Range 8.0 – 18.0 mg/dL
Critical Range > 100.0 mg/dL

Affected by protein intake and hydration

Related Conditions

Kidney Disease High

Food & Lifestyle Recommendations

🍎 Food If due to dehydration: increase water intake; if due to high protein: moderate protein intake BUN rises with high protein intake and falls with hydration
🍎 Food Reduce excessive protein intake if above 1.2g/kg/day High protein intake increases urea production; moderate protein is appropriate for kidney health
🍎 Food Stay well-hydrated — dehydration elevates BUN disproportionately to creatinine Dehydration increases BUN more than creatinine, raising the BUN/creatinine ratio
🍎 Food Limit processed meats and high-purine foods if gout is a concern High purine intake can stress kidney function and increase nitrogenous waste
💡 Other Stay well-hydrated — aim for pale yellow urine as a hydration guide Dehydration concentrates BUN disproportionately to creatinine

Evidence-Backed Supplements

When High

  • Probiotics Tier A May Decrease

    Moderate evidence; probiotics may reduce uremic toxins by modifying gut microbiota. Shown to lower BUN in some CKD trials.

    Multi-strain probiotic (Lactobacillus + Bifidobacterium) 5–50 billion CFU/day Morning on empty stomach
    PMID 36001877 PMID 25927096 PMID 32128794
  • Omega 3 Tier A May Decrease

    Limited evidence; omega-3 may have renoprotective effects. Some studies show modest BUN reduction in CKD patients.

    Fish oil (EPA+DHA) 1000–2000 mg EPA+DHA/day With meals
    PMID 30019766 PMID 32114706 PMID 30480773

When Low

  • Zinc Tier A May Increase

    Limited evidence; zinc supplementation may help in malnutrition-related low BUN. Low BUN usually indicates liver disease or malnutrition.

    Zinc picolinate or bisglycinate 15–30 mg/day Evening, away from iron/calcium
    PMID 33724446 PMID 36994923 PMID 27996088

Questions to Ask Your Doctor

  • Is my elevated BUN due to kidney issues, dehydration, or high protein intake? BUN:Cr ratio >20 suggests dehydration or GI bleed
  • Does my elevated BUN indicate kidney problems, or could it be from dehydration? High BUN can indicate kidney dysfunction, dehydration, or high protein intake. BUN-to-creatinine ratio helps differentiate.

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