The effect of dietary factors on the risk of developing urinary tract infection

Abstract

Sirs, In a recent paper in the April 2004 issue of Pediatric Nephrology, Kontiokari et al.[1] reviewed epidemiological and interventional trials evaluating the effect of dietary factors on the risk of urinary tract infection (UTI). They concluded that some food items were associated with a lower risk of UTI in an adult population, probably due to an impact on the bacterial composition of stools. We would like to stress a further possible mechanism, namely the effect of alimentary acid load on urine pH.Average net endogenous acid excretion of common mixed western diets, measured as urinary net acid excretion, varies from~40 to 80 mEq/day. Although scientists have known for several decades that the composition of the diet influences the urine pH, only recently has experimental and theoretical evidence been provided that it is possible to reliably calculate the potential renal acid load of foods and thus to estimate its influence on urine pH [2]. Patients with reduced renal function (e.g., preterm neonates and elderly persons) have a risk of suffering pathophysiological sequelae ("incipient late metabolic acidosis", chronic low-grade metabolic acidosis) of a food with a high acid load [3]. A possible chronic impact of food-borne acid load on urinary stone disease is generally accepted [4], and, for example, the effect on osteoporosis is still under discussion [5].Acidification of urine by special dietary elements has been recommended as a therapy to reduce the risk of UTI. Dietary additives, already investigated in the "pre-antibiotic" era for this purpose, and partly still in use today (especially in patients with a high risk of recurrent UTI), include methionine [6], methenamine (formation of formaldehyde in acidic urine) [7], vitamin C [8], and cranberry juice (acidification of urine, reduction of bacterial adherence) [9]. Only recently was acidification of urine presented as a "new therapeutic strategy" for the treatment of UTI caused by nitrate-reducing bacteria (bacteriostatic effect due to generation of nitric oxide and other toxic reactive nitrogen intermediates in acidic urine) [10].The food items in the epidemiological and interventional trials reviewed by Kontiokari et al. [1, Table 1] include cranberry juice (involved in seven trials; five found to be protective) and vitamin C or "vitamins including vitamin C", respectively (three trials, one protective). Thus, taking into account the effect of dietary elements on urine pH (and/or on the bacterial adherence in the urinary tract [9]) may result in a broader interpretation of this interesting analysis of data pointing to a possible linkage between nutrition (e.g., functional food) and susceptibility for UTI. References1. Kontiokari T, Nuurinen M, Uhari M (2004) Dietary factors affecting susceptibility to urinary tract infection. Pediatr Nephrol 19:378-383 2. Remer T, Manz F (1995) Potential renal acid load of foods and its influence on urine pH. J Am Diet Assoc 95:791-797 3. Kalhoff H, Manz F (2001) Nutrition, acid-base status and growth in early childhood...