尿路結石症の分析疫学的考察

Abstract

In this paper, urolithiasis is reviewed from the standpoint of analytical epidemiology, which examines a statistical association between a given disease and a hypothesized factor with an aim of inferring its causality. Factors incriminated epidemiologically for stone formation include age, sex, occupation, social class (level of affluence), season of the year and climate, dietary and fluid intake and genetic prodisposition. Since some of these factors are interlinked, they are broadly classified into five categories and epidemiologically looked over here. Genetic predisposition is essentially endorsed by the more frequent episodes of stone formation in the family members of stone formers, as compared to non-stone formers. Nevertheless, some environmental factors (likely to be dietary habits) shared by family members are believed to be relatively more important than genetic predisposition. A hot, sunny climate may influence stone formation through inducing dehydration with increased perspiration and increased solute concentration with decreased urine volume, coupled with inadequate liquid intake, and possibly through the greater exposure to ultraviolet radiation which eventually results in an increased vitamin D production, conceivably correlated with seasonal variation in calcium and oxalate excretion to the urine. Urinary tract infections are importantly involved in the formation of magnesium ammonium phosphate stones in particular. The association with regional water hardness is still in controversy. Excessive intake of coffee, tea and alcoholic beverages seemingly increase the risk of renal calculi, though not consistently confirmed. Many dietary elements have been suggested by numerous clinical and experimental investigations, but a few elements are substantiated by analytical epidemiological investigations. An increased ingestion of animal protein and sugar and a decreased ingestion of dietary fiber and green-yellow vegetables are linked with the higher probability of stone formation in the industrialized countries. No trace elements in foodstuffs and liquids have been epidemiologically associated. The dietary guidelines for avoiding stone formation and/or recurrence are summarized in this paper, including other daily-life recommendations.