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Ethnic differences in titratable acid excretion and bone mineralization.
Henrikas Vaitkevicius1, Richard Witt, Matthew Maasdam
1Department of Medicine, Wayne State University School of Medicine, Detroit, MI, USA.
Medicine and Science in Sports and Exercise
|February 6, 2002
Summary
Racial differences in urinary acid excretion influence calcium and sodium levels. These variations in titratable acid excretion may explain ethnic differences in bone health and stress fracture risk.
Area of Science:
- Nephrology
- Bone Metabolism
- Human Physiology
Background:
- Urinary calcium excretion varies between ethnic groups.
- Ethnic differences in acid metabolism may underlie variations in calcium and sodium excretion.
- Understanding these differences is crucial for bone health and stress fracture prevention.
Purpose of the Study:
- To investigate if ethnic variations in acid (H+) metabolism contribute to differences in urinary calcium excretion between Black and White individuals.
- To determine if increased titratable acid excretion is associated with a predisposition to stress fractures.
Main Methods:
- Acute administration of ammonium chloride (NH4Cl) to healthy Black and White volunteers to measure urinary sodium, calcium, and acid excretion.
- Assessment of Na+/H+ antiporter activity using acid-loaded platelets as surrogate markers.
- Comparison of titratable acid excretion in athletes with and without a history of stress fractures.
Main Results:
- Increased titratable urinary acid excretion correlated with changes in renal calcium and sodium excretion.
- Whites exhibited significantly higher basal and NH4Cl-induced acid excretion and higher baseline calcium excretion compared to Blacks.
- Blacks showed attenuated Na+/H+ exchange activity, while whites experienced decreased sodium excretion post-acid loading.
- Athletes with stress fractures had enhanced basal H+ and phosphate excretion compared to those without.
Conclusions:
- Ethnic differences in sodium and calcium excretion may stem from racial variations in renal H+ excretion.
- Blacks may possess a greater endogenous buffering capacity than Whites.
- Heritable differences in titratable acid excretion likely mediate ethnic variations in bone mineralization and integrity, as well as stress fracture risk in athletes.