What is Blood Urea Nitrogen?
BUN measures the amount of nitrogen in your blood that comes from urea. When you eat protein or muscle tissue is broken down, nitrogen waste is produced. The liver converts this waste into urea, which is then filtered by the kidneys and excreted in urine.
Because urea is highly dependent on fluid volume in the blood, BUN is a sensitive marker for both kidney filtration rate and hydration.
Why Does BUN Matter?
BUN is a useful metabolic biomarker for:
- Tracking whether your kidneys are effectively removing nitrogen waste from the bloodstream
- Gauging protein metabolism by showing the nitrogen load created by your diet and muscle turnover
- Evaluating hydration status, since urea levels rise when you’re dehydrated
- Assessing liver function, since the liver needs to convert ammonia into urea for safe disposal
- Identifying muscle breakdown to determine if training intensity is exceeding your body’s ability to clear tissue byproducts
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How to Interpret BUN?
(Ranges may vary slightly by lab)
Standard reference ranges represent the middle 95% of healthy individuals but don’t necessarily reflect levels associated with longevity. Optimal ranges are derived from clinical guidelines, peer-reviewed research, and real-world outcomes data, with an emphasis on levels associated with peak functioning and reduced disease risk.
Benefits of Optimizing BUN
- Improved mental clarity
- Efficient waste removal
- Improved cardiovascular efficiency1
- Lower risk of chronic kidney disease and cardiovascular strain
- Improved blood glucose control2
- May lower risk of depression3
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Low BUN Levels
Low BUN levels typically indicate a systemic lack of protein or a breakdown in the liver’s ability to process nitrogen.
Symptoms:
- Muscle loss
- Poor strength
- Slow recovery
- Fatigue
- Brain fog (in more severe, prolonged cases)
Causes:
- Pregnancy (this is normal)
- Low-protein diets
- Malnutrition
- Overhydration
- Liver disease
Healthspan Impacts:
- Increased risk of sarcopenia (muscle loss)4
- Reduced ability to adapt to metabolic stress
- Higher risk of cirrhosis (scarring of the liver)5
- Increased risk of frailty in older adults6
High BUN Levels (Uremia)
Elevated BUN indicates nitrogen waste is accumulating in the blood, most commonly due to dehydration, reduced kidney clearance, increased protein intake or muscle tissue breakdown.
Symptoms:
- Fatigue and weakness
- Nausea and poor appetite
- Headaches
- Dizziness
- Insomnia
- Ammonia-like breath
- Itchy skin
Causes:
- Dehydration
- High-protein diets
- Kidney issues
- Heart failure
- Gastrointestinal bleeding
- Certain medications that impair kidney function
- Diabetes
- High blood pressure
Healthspan Impacts:
How Hone Treats Out of Range BUN
Your Hone physician will interpret your BUN levels with creatinine, BUN/Creatinine ratio, albumin, and electrolytes, alongside your symptoms and health context to map out a personalized treatment plan.
- IV fluids* – to correct high BUN levels due to dehydration
- Medication adjustments *- stopping or starting certain medications such as NSAIDs or diuretics
- Condition management* – treating the underlying condition (e.g., kidney disease)*
*Your Hone Physician does not prescribe these treatments but will recommend further evaluation and help coordinate care with your primary care provider when medical treatment is indicated.
- Consume an antioxidant-rich, purine-low diet13, 14
- Stay hydrated
- Make sure you’re getting optimal dietary fiber (whole grains, legumes, vegetables)15
- Aim for ~0.35–0.55 g of protein per pound of body weight per day (moderate protein intake if dealing with elevated BUN levels)
- Prioritize sleep, as short sleep can cause a rise in BUN16
Jiang, R., et al. (2025). Blood urea nitrogen and cardiovascular disease risk: Evidence from the CHARLS cohort study. Medicine.
↑Xie, Y., et al. (2018). Higher blood urea nitrogen is associated with increased risk of incident diabetes mellitus. Kidney International.
↑Mao, Y., et al. (2022). Associations between urea nitrogen and risk of depression among subjects with and without type 2 diabetes: A nationwide population-based study. Frontiers in Endocrinology.
↑Kameda, M., et al. (2021). Reduced uremic metabolites are prominent feature of sarcopenia, distinct from antioxidative markers for frailty. Aging (Albany NY).
↑Lin, H., et al. (2021). U-shaped relationship between urea level and hepatic decompensation in chronic liver diseases. Clinical and Molecular Hepatology.
↑Chen XX, et al. (2023). Blood urea nitrogen to creatinine ratio is associated with physical frailty in older-aged Chinese: a cross-sectional study. Aging Clin Exp Res.
↑Li, R., & Li, C. (2025). Association between blood urea nitrogen concentration and diabetic foot ulcer: A retrospective cross-sectional study based on NHANES. Medicine.
↑Mei, T., et al. (2025). Exploratory Genome-Wide association study of blood urea nitrogen levels in elite Chinese winter sports athletes. Gene.
↑Jiang, R., et al. (2025). Blood urea nitrogen and cardiovascular disease risk: Evidence from the CHARLS cohort study. Medicine.
↑Lan, Q., et al. (2021). The Value of Blood Urea Nitrogen in the Prediction of Risks of Cardiovascular Disease in an Older Population. Frontiers in Cardiovascular Medicine.
↑Bandeira Fagundes, et al. (2018). Probiotics in the treatment of chronic kidney disease: A systematic review. Jornal Brasileiro de Nefrologia.
↑Zeinalabedini, M., et al. (2025). The Effect of Omega-3 Supplements on Renal Function Indices in Chronic Kidney Patients Undergoing Hemodialysis. Nutrition and Metabolic Insights.
↑Omid, N., et al. (2024). Association of dietary antioxidant indices with kidney function indicators in patients with type 2 diabetes: A cross-sectional study. Scientific Reports.
↑Chen Z, et al. (2024). Effect of low-purine diet on the serum uric acid of gout patients in different clinical subtypes: a prospective cohort study. Eur J Med Res.
↑Wathanavasin, W., et al. (2025). Effects of Dietary Fiber Supplementation on Modulating Uremic Toxins and Inflammation in Chronic Kidney Disease Patients: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Toxins.
↑S. Onvani, M. et al. (2019). Short sleep duration is related to kidney-related biomarkers, but not lipid profile and diet quality in diabetic nephropathy patients. International Journal for Vitamin and Nutrition Research.
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Reviewed for Accuracy by Our Medical Review Board
This biomarker information has been reviewed by a member of Hone’s medical review board. As part of the medical review team, physicians fact-check this content against the latest research and their own experience treating their patients.
Ashley Winter, M.D., is a board-certified urogynecologist trained at Weill Cornell and Cleveland Clinic. She specializes in female and male sexual dysfunction, urinary issues, genital pain, and hormone therapy.
James Staheli, D.O., is the Medical Director for Broad Health, Hone Health’s affiliated medical practice and a family medicine doctor in Atlanta, Georgia.
