The epidemiology of gallstones in women
A survey of 652 nonvegetarian and 130 vegetarian women aged 40-70 years using real-time ultrasonography was carried out to determine the prevalence of gallstones. 24.6% of nonvegetarian women were found to have gallstones compared with 11.5% of vegetarian women (p < 0.05). Each participant completed a postal questionnaire on general health aspects and dietary habits. Aetiological factors shown to have a strong influence on the development of gallstones included increasing age, obesity and positive family history. The prevalence of gallstones increased steadily with age (p < 0.01) and obesity (p < 0.001). Women with gallstones were much more likely to have a first degree relative with a history of gallstones (p < 0.01). The vegetarian participants were younger and less likely to be obese than the nonvegetarian participants but/ even after correction for these confounding influences/ gallstones were significantly less prevalent in vegetarian women (p < 0.05). Other aetiological factors that have been purported to to be risk factors in the pathogenesis of gallstones but were not shown to be so in this study were parity, exogenous oestrogen intake and a history of smoking. In order to further study the effect of diet in the pathogenesis of gallstones, an age-matched case-control study was carried out using the women with gallstones identified in the prevalence survey as cases and women proven to be free of gallstones as the controls. 107 nonvegetarian and 12 vegetarian pairs completed a four-day dietary diary and were subsequently interviewed about their dietary habits, exogenous oestrogen intake and upper gastrointestinal symptomatology. There were no significant differences in energy intake/ total protein and animal and vegetable protein, fat and cholesterol, carbohydrate, simple sugars and fibre intake in the diet consumed by cases compared with controls. Vegetarian women, however, ate a very different diet to the nonvegetarian women suggesting that diet does play an important role in the pathogenesis of gallstones. Failure to demonstrate a dietary association in the case-control study may be due to the fact that the overwhelming majority of people in western communities consume a diet that is too high in fat, animal protein and simple sugar content and too low in unrefined starches to be able to detect any dietary differences between cases and controls - the threshold effect. Another important aspect of gallstone disease revealed by the study was the proportion of cases shown to be asymptomatic. Over 70% of all cases had not been previously diagnosed. Moreover, the case-control study showed that cases were no more likely to suffer from "biliary" symptoms than controls except for those symptoms associated with acute cholecystitis or common bile duct obstruction. These data provide persuasive support for the conservative management of asymptomatic gallstones.