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Don’t Forget the Acid Base Status When Studying Metabolic and Clinical Effects of Dietary Potassium Depletion

Research Institute of Child Nutrition D-44225 Dortmund, Germany

Address correspondence to: Thomas Remer, Ph.D., Research Institute of Child Nutrition, D-44225 Dortmund, Germany. E-mail: remer{at}fke-do.de

To the editor:

In the June 2001 issue of JCEM Coruzzi et al. (1) reported an increased systolic blood pressure and an elevated urinary calcium excretion in patients with essential hypertension after a 10-d period with low potassium intake.

It is now well established that reducing the alkali load (or increasing the acid load) in the diet can substantially increase urinary calcium excretion (2, 3, 4, 5, 6, 7). If, for example, 20 mmol (3.0 g/d) of the acidifying amino acid L-methionine is added to a diet (under controlled experimental conditions) a marked increase in urinary calcium excretion (averaging 36 mg/d) occurs in response to the rise in renal net acid excretion (of about 40 mEq/d) in healthy adult volunteers (3). Despite this known impact of changes in the acid base status on calcium metabolism, Coruzzi et al. (1) did not provide any information as to which kind of potassium salt was used in their study during the period of normal potassium intake.

Did the authors administer an alkalizing potassium salt (e.g. potassium bicarbonate or tripotassium citrate) or did they use potassium chloride instead? Potassium chloride has a small acidifying effect due to the lower intestinal net absorption of the potassium cation as compared with the chloride anion (7, 8).

The marked positive impact of oral administration of alkalizing potassium bicarbonate on the calcium and phosphorus balance (), bone resorption (), and bone formation () has been demonstrated especially by Sebastian et al. (4) in postmenopausal women. Similar effects on calcium metabolism in women have been observed after administration of alkalizing sodium (instead of potassium) bicarbonate (2). Thus, it is possible that the changes in urinary calcium excretion observed by Coruzzi et al. (1) may not be primarily due to the cation potassium per se, but could also have been caused by the alkalizing effect of the corresponding anion.

In principle, endocrine, metabolic and/or clinical effects resulting from an altered mineral intake are not necessarily due to the mineral cation itself but may result from an altered acid base status, too. Therefore, for similar studies it seems necessary to take potential renal acid loads (5, 8, 9) of both mineral salts and foods into account and to control parameters of acid base metabolism.

Received August 23, 2001.

References

1. Coruzzi P, Brambilla L, Brambilla V, Gualerzi M, Rossi M, Parati G, Di Rienzo M, Tadonio J, Novarini A 2001 Potassium depletion and salt sensitivity in essential hypertension. J Clin Endocrinol Metab 86:2857–2862[Abstract/Free Full Text]
2. Lutz J 1984 Calcium balance and acid-base status of women as affected by increased protein intake and by sodium bicarbonate ingestion. Am J Clin Nutr 39:281–288[Abstract/Free Full Text]
3. Remer T, Manz F 1994 Estimation of the renal net acid excretion by adults consuming diets containing variable amounts of protein. Am J Clin Nutr 59:1356–1361[Abstract/Free Full Text]
4. Sebastian A, Harris ST, Ottaway JH, Todd KM, Morris Jr RC 1994 Improved mineral balance and skeletal metabolism in postmenopausal women treated with potassium bicarbonate. N Engl J Med 330:1776–1781[Abstract/Free Full Text]
5. Barzel US, Massey LK 1998 Excess dietary protein can adversely affect bone. J Nutr 128:1051–1053[Abstract/Free Full Text]
6. Lemann Jr J 1999 Relationship between urinary calcium and net acid excretion as determined by dietary protein and potassium: a review. Nephron 81(Suppl 1):18–25
7. Remer T 2000 Influence of diet on acid-base balance. Semin Dial 13:221–226[CrossRef][Medline]
8. Remer T, Manz F 1995 Potential renal acid load of foods and its influence on urine pH. J Am Diet Assoc 95:791–797[CrossRef][Medline]
9. Trinchieri A, Zanetti G, Curro A, Lizzano R 2001 Effect of potential renal acid load of foods on calcium metabolism of renal calcium stone formers. Eur Urol 39(Suppl 2):33–36

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