The Human Body Maintains a Tightly Regulated Alkaline Blood pH
The human body's blood is slightly alkaline, with a normal pH range of 7.36-7.44, and deviations from this narrow range represent life-threatening metabolic or respiratory acidosis or alkalosis. 1, 2
Blood pH Regulation
The blood pH is maintained within the tight range of 7.36-7.44 through multiple buffering systems, with serum bicarbonate (normal range 22-26 mmol/L) serving as the primary buffer to maintain acid-base balance. 2
Blood pH below 7.35 indicates acidemia (whether from metabolic or respiratory causes), while pH above 7.44 indicates alkalemia, both representing pathological states requiring intervention. 3, 4
pH Variation Across Body Compartments
While blood is alkaline, pH varies dramatically across different body compartments:
- Stomach: pH 1-2 (highly acidic for digestion) 5
- Blood: pH 7.36-7.44 (slightly alkaline) 1, 2
- Skin surface (stratum corneum): pH 4.1-5.8 (acidic for antimicrobial barrier and barrier function) 5
- Urine: pH typically 5.5-6.5, varying with diet and metabolic state 6
Dietary Impact on Acid-Base Balance
Western diets high in animal protein and low in fruits/vegetables create chronic low-grade metabolic acidosis by producing nonvolatile acids from sulfur-containing amino acids, while fruits and vegetables provide potassium citrate salts that generate alkali to buffer acids. 2, 7
The body compensates for dietary acid load by borrowing alkaline reserves from bone and increasing renal acid excretion, but with aging and declining kidney function, this compensation becomes less effective, risking chronic interstitial acidosis. 7, 8
Clinical Significance
Maintaining serum bicarbonate ≥22 mmol/L is critical to prevent metabolic acidosis complications including bone demineralization, protein catabolism, muscle wasting, and chronic kidney disease progression. 2
In chronic kidney disease patients, serum bicarbonate should be monitored monthly and maintained at or above 22 mmol/L, as impaired renal function reduces the kidney's ability to excrete hydrogen ions and synthesize ammonia. 2
Common Pitfall
Do not confuse the body's overall acid-base status with localized pH variations—while blood must remain alkaline (pH 7.36-7.44) for survival, other body compartments like the stomach and skin surface are intentionally acidic for their specific physiological functions. 5