This is a large retrospective study to evaluate the prevalence and risk factors of GBP in northwest Chinese population. The prevalence in the current study of GBP (7.8% ) is higher than a Beijing Center study (6.9%)[11], but lower than previously reported in Taiwan (9.5%) [3], similar to a Zhejiang area study (7.4%)[14]. Results from Korea study has a prevalence of 5.4%[15], while Japanese study shows a prevalence of 5.6% [1]. The estimated prevalence is about 5% of the global population[3]. Compared with the prevalence of GBP in western society (1.0-6.9%) [16–18], Asian, especially Chinese, had a higher tendency to develop GB polyps. The reason for the vary prevalence rates of GBP may be related with the difference among countries and regions. For example, Japanese study reported regional and temporal differences in the prevalence of GBP ,and it was 3.9% in a rural area in 1988 and 12.3% in an urban area in 1933[19]. On the other hand, the increase of life expectancy, health awareness and ultrasound resolution may be the reasons. In this study the multilevel mixed-effects logistic regression analysis showed that gender and BMI were independent risk of GBP, and the risk of GBP in men was significantly higher than that of women. The risk of GBP in men was 1.43 times higher than in women, and in obesity was 1.29 times higher than in normal weight people. Males and those with higher BMI were at a high risk of developing GBP.
Rates in healthy adults according to gender indicated a higher prevalence of GBP in men[3, 20], which consistent with our study. The formation of GBP is still unclear, the majority of GBP are benign, and are most commonly cholesterol polyps with a prevalence of about 46–70% [5, 21]. Acyl-CoA: cholesterol acyltransferase 2 (ACAT2) is an estrogen-sensitive enzyme facilitating the cholesteryl ester incorporation into apoprotein B and papillary hyperplasia in the gallbladder mucosa. Estrogen, a sex steroid hormone, can impair the esterification of cholesterol by reducing the activity of both hepatic and intestinal ACAT2[22]. Cholesterol polyp is characterized by excessive accumulation of cholesteryl esters in gallbladder mucosa, which is a local manifestation of cholesterol metabolic disorder[23]. In this study, we saw the narrow gap of prevalence between male and female in 51–60 years compared with participants in 41–50 years, in accordance with the decreasing of estrogen in postmenopausal. And the prevalence of GBP for female and male were almost the same over 61 years. These results indicate that estrogen may be a protective factor from the development of GBP.
Gallbladder mucosa esterifies sterols, absorbs lipids, and synthesizes triglycerides and cholesterol to form cholesterol crystals[24, 25]. On the other hand, it may be due to cholesterol deposition in the blood, similar to the formation of atherosclerotic plaque[26]. GBP has been confirmed to be associated with increased risk of coronary heart disease[24]. In the present study, however, we found no association between lipid level, FBG, blood pressure and the risk of GBP by multilevel mixed-effects logistic regression analysis.
Obesity and its complications (including metabolic syndrome, type 2 diabetes, cardiovascular disease, and cancer, etc.) are a global pandemic, and was found to be most strongly associated with the risk of GBP in the present study. We found the prevalence of GBP was increased with BMI. The lean group (BMI < 18.5) has the lowest prevalence of 3.6%, and the normal weight group (BMI 18.5–25) has a higher of 7%, while the overweight (BMI25-27.5) and obesity group(BMI ≥ 27.5) have the same prevalence of 9%. But the results are always contradictory. Lin[3] and Jorgensen [27] reported the prevalence of GBP was not associated with BMI, weight factors, glucose or lipid profile. However, Segawa K suggested that obesity contributed to the development of cholesterol polyps, which showed the prevalence of GB polyps rose in accordance with the rise in obesity index, which was highest among the middle-aged (40–51 years), similar to the curve of the obesity index[1]. Obesity, as well as dysfunction of lipid profile, high blood glucose and high FBG were the diagnose criteria of Metabolic syndrome (MS). In Lim’s study, multivariate logistic regression analysis revealed MS was the risk factor for GBP, but not other components of FBS, serum lipid and blood pressure[20]. Another study shows a higher non-HDL-c/HDL-c ratio is independently related to a higher risk of GBP formation in Chinese men[28]. These metabolic components may be combined to have an effect of the GBP developing. As the increasing prevalence of obesity and MS, keeping BMI and metabolic index under normal range is important to decrease the rising of GBP. Compared with non GBP group, the levels of age, DBP and UA, Cr, BUN in GBP group were statistically significant; however, these variables had no significant correlation in multivariate logistic regression analysis. These results showed that no blood biochemistry index could measure the risk of GBP.
This study has several limitations. First, patients come from one health screening center and therefore can only represent the limited areas. Second, regardless of size and type, cholesterol polyps, adenomatous polyps, and inflammatory polyps were included in the GBP group, may have an impact on the results. However, it is difficult to make a clear histological diagnosis of GBP by means of noninvasive ultrasound alone. Future studies should attempt to classify GBP by histological findings after surgery.
In conclusion, GBP found incidentally during abdominal ultrasound appear to be strongly associated with gender and metabolic index. Our study imply that male gender and BMI were independent risk factors for prevalence of GBP, and obesity contributes to the formation of GBP. In the future, it is necessary to clarify the relationship between obesity and GBP according to the histological classification and the mechanism of obesity on the formation of GBP.