Abstract
Background and Aims
Insulin resistance is associated with prevalent gallstones, but its effect on initial gallstone formation is not well understood.
Methods
We conducted a nested case-control study to examine whether insulin resistance is a risk factor for initial gallbladder sludge and stone formation during pregnancy. Cases were 205 women with new gallbladder sludge and stones during pregnancy and the early post-partum. Controls were 443 randomly selected women without sludge or stones during pregnancy. Gallbladder ultrasounds were obtained in each trimester, and at 4–6 weeks postpartum. Fasting serum glucose, lipids, and insulin were measured at 26–28 weeks gestation. Insulin resistance was measured by the homeostasis model. Logistic regression was used to identify independent risk factors for gallstone formation.
Results
Insulin resistance was significantly greater in cases than controls on univariate analysis (p<0.001). Pre-pregnancy body mass index was strongly associated with gallstone formation on univariate analysis (p<0.001), but this association was diminished after adjusting for insulin resistance (p=0.01). On multivariate analysis, insulin resistance was significantly associated with gallstone formation (p=0.004), even after adjustment for pre-pregnancy body mass index and other confounding factors including HDL cholesterol and physical activity. This association was strongest in women with pre-pregnancy body mass index <30 kg/m2.
Conclusions
Insulin resistance is a risk factor for incident gallbladder sludge and stones during pregnancy, even after adjustment for body mass index. Insulin resistance may represent a causal link between obesity and overweight and gallstones.
Introduction
In the United States, gallstone disease is one of the most common and costly of all digestive diseases, requiring more than 700,000 cholecystectomies annually 1. Prior cross-sectional studies have shown that body mass index (BMI), obesity, and diabetes are significantly associated with gallstones and biliary sludge 2–6. In addition, serum insulin and C-peptide levels are associated with gallstone prevalence 2. However, these studies examined prevalent gallstones, and therefore could not clearly define risk factors for initial development of gallbladder sludge or stones.
Parity is a significant risk factor for gallstones, and pregnancy is a high-risk period for gallstone formation 7–9. We have previously shown that the risk of forming gallbladder sludge or stones during pregnancy is significantly higher in obese women (BMI ≥30 kg/m2) than in normal weight (BMI <25 kg/m2) or overweight (BMI 25.0–29.9 kg/m2) women 10. Gallbladder sludge, a mixture of cholesterol and calcium bilirubinate crystals in bile, can be detected ultrasonographically and is generally felt to represent a precursor stage potentially leading to formation of actual gallstones 11. Insulin resistance, which increases with body mass index, is one possible mechanism linking obesity to gallstones 2, 12–15. However, not all studies confirm this association 16, 17. Previous studies examining insulin resistance and gallstones have been retrospective or cross-sectional, and it is difficult to determine if insulin resistance has a causal effect in gallstone formation. The aim of this study was to examine prospectively the effect of insulin resistance and gestational diabetes on initial development of gallstones during pregnancy.
Methods
We conducted a nested case-control study within a prospective cohort study of gallbladder disease during pregnancy 10. The study was approved by the Institutional Review Boards of the University of Washington and Madigan Army Medical Center, and all women gave written informed consent. Potentially eligible women were approached for the study at their first obstetrics visit at Madigan Army Medical Center. Women were excluded because of age less than 18 years, language comprehension, plans to move away within 3 months, or presenting for prenatal care after 20 weeks gestation. Enrolled subjects underwent serial fasting gallbladder ultrasound examinations at 10–12 weeks gestation, 17–19 weeks gestation, 26–28 weeks gestation, and 4–6 weeks postpartum. Study questionnaires and interviews were completed at study entry, during the early third trimester, and in the early postpartum period, and covered past medical history, gastrointestinal symptoms, physical activity, behavioral factors such as smoking or alcohol intake, and dietary intake (entry and postpartum questionnaires only). Pre-pregnancy BMI was calculated from subjects’ height measured at study entry and self-reported weight before pregnancy. Self-reported pre-pregnancy weight correlated significantly with weight measured at study entry (Spearman’s correlation coefficient=0.94, p<0.001). Waist circumference was measured by research personnel at study entry (10–12 weeks gestation).
Fasting blood samples were drawn at 26–28 weeks gestation and tested for serum lipid and glucose levels. Gestational diabetes was diagnosed based on standard clinical criteria. Using serum samples stored at −70°C from this blood draw, total immunoreactive insulin was measured by a double-antibody radioimmunoassay developed by the Diabetes Endocrinology Research Laboratory at the University of Washington. We used the Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) to assess insulin resistance from fasting glucose and insulin levels 18. HOMA-IR is calculated as (fasting insulin [mU/ml] × fasting glucose [mmol/L]) ÷ 22.5), with greater values of HOMA-IR indicating increasing degrees of insulin resistance. HOMA-IR has been shown to correlate well with insulin resistance in men and non-pregnant women as measured by more complicated measures such as the euglycemic hyperinsulinemic clamp 18. Estradiol levels were measured by radioimmunoassay (ICN Biomedicals, Inc., Costa Mesa, CA) and progesterone levels by enzyme-linked immunoassay (Systems Labs, Inc., Webster, TX) from these samples.
Physical activity during the second and third trimesters was assessed by a modification of the CARDIA Physical Activity History instrument 19. Women indicated the months in which they participated in each of 8 categories of vigorous and 5 categories of moderate physical activity for at least 1 hour per week. Duration in hours and minutes per week was recorded. To account for a possible confounding effect of physical activity, we calculated the volume of physical activity in the second and third trimesters of pregnancy. We multiplied the average duration of activity per week of each activity by its metabolic equivalent units (METs) to determine the average MET-hours per week for each activity 20. One MET is the rate at which adults utilize energy at rest. We then summed over all activities to get an overall index of MET-hours. We divided women into quartiles of total activity based upon the calculated MET-hours for the second and third trimesters.
Gallbladder ultrasonography was performed with a standard imaging protocol using a 3.5–7.0 MHz rotatory sector scanning transducer (ATL Inc., Bothell, WA, or Acuson Corporation, Mountain View, CA). All study ultrasounds were performed by sonographers with special training in gallbladder ultrasound and with women fasting or having drank only sips of water. Findings were recorded by the sonographers, and images and findings were reviewed by one of two designated study radiologists with expertise in gallbladder ultrasound. Sludge was defined as the presence of low-level echoes that shift with position changes and without post-acoustic shadowing. Stones were defined as high-amplitude echoes greater than 2 millimeters in diameter with post-acoustic shadowing. In 10,887 scans performed in the entire study, there were discrepancies between the radiologist’s and the sonographer’s readings in 70 regarding the diagnosis of sludge (kappa=.93) and in 25 regarding the diagnosis of stones (kappa=.98). In case of discrepancy, the radiologist’s reading was accepted as correct.
Of the 8,929 women approached, 4,897 (55%) were eligible and interested for the parent cohort study. We excluded an additional 208 women with stones on entry ultrasound and 33 women with a prior cholecystectomy. Two interpretable study ultrasounds were available for 3,254 women. For this case-control study, cases (n=205) were defined as women without gallbladder sludge or stones on the entry ultrasound, and who subsequently developed new gallbladder sludge or stones on any study ultrasound. Controls (n= 512) were randomly selected using a random number table from subjects in the parent study without gallbladder sludge or stones on any ultrasound. Sixty-nine controls did not have serum available, leaving 443 controls for analysis. The timing and number of available ultrasounds was similar in cases and controls (3.1±0.7 in cases vs. 3.2±0.7 in controls, p=0.47). Cases and controls were not matched on any variables, and women with pre-existing or gestational diabetes were eligible for inclusion in this study.
The distributions of categorical and continuous variables were compared by the chi-square test, Student’s t-test, or the Wilcoxon sign-rank test as appropriate. Multiple logistic regression was used to examine the association of insulin resistance with gallbladder disease after adjustment for other factors (Stata 8.0, Stata Corp., College Station, TX). Variables considered for inclusion were those previously shown to be associated with gallbladder disease (parity, weight gain during pregnancy, HDL cholesterol) 10, demographic variables (age, race, ethnicity), alcohol consumption, and variables potentially related to maternal weight (pre-pregnancy body mass index, waist circumference at entry, waist-hip ratio at entry) or insulin resistance (glucose and lipid levels). Variables that were significant with p<0.1 were retained in the final model. Significance of the regression models was tested with the likelihood-ratio statistic.
Results
Cases and controls were similar in age, race, and parity (Table 1). Women who developed sludge or stones were more likely to be Hispanic than control women. In addition, women who developed sludge or stones had significantly higher pre-pregnancy BMI and waist circumference, but not waist-hip ratio, at entry. Both weight gain during pregnancy and serum HDL cholesterol levels were inversely associated with the risk of developing sludge or stones. Fasting serum glucose levels and the prevalence of clinically diagnosed gestational diabetes mellitus were similar in cases and controls. However, serum insulin levels and HOMA-IR were significantly higher in cases than in controls, suggesting greater degrees of insulin resistance in women who formed sludge or stones even in the absence of clinically diagnosed gestational diabetes.
Table 1.
Selected characteristics of study subjects
| No sludge or stones (n=443) | Sludge or stones (n=205) | p-value | |
|---|---|---|---|
| Age, years (mean ± SD) | 25.1 ± 4.8 | 24.9 ± 4.4 | 0.64 |
| Race (n, %) | 0.20 | ||
| White | 324 (72.3) | 148 (70.5) | |
| African-American | 53 (11.8) | 20 (9.5) | |
| Asian/Pacific Islander | 26 (5.8) | 10 (4.8) | |
| Native American | 8 (1.8) | 2 (1.0) | |
| Other/mixed | 37 (8.3) | 30 (14.2) | |
| Hispanic ethnicity (n, %) | 39 (8.7) | 34 (16.2) | 0.004 |
| Parity (median, interquartile range) | 1 (0–2) | 1 (0–2) | 0.93 |
| Waist circumference at entry, cm (mean ± SD) | 86.2 ± 13.4 | 88.9 ± 14.7 | 0.02 |
| Waist-hip ratio at entry (mean ± SD) | 0.83 ± 0.07 | 0.83 ± 0.07 | 0.52 |
| Weight gain during pregnancy, kg (mean ± SD) | 14.2 ± 5.9 | 12.7 ± 7.3 | 0.007 |
| Pre-pregnancy body mass index, kg/m2 (mean ± SD) | 24.5 ± 5.0 | 26.9 ± 6.5 | <0.001 |
| Alcohol use during pregnancy (n, %) | 130 (29.0) | 48 (22.9) | 0.09 |
| MET-hours per week of vigorous physical activity, 2nd trimester (median, interquartile range) | 118 (62, 186) | 95 (44, 171) | 0.01 |
| MET-hours per week of vigorous physical activity, 3rd trimester (median, interquartiles range) | 102 (50, 164) | 99 (40, 172) | 0.26 |
| Gestational diabetes (n, %) | 8 (1.8) | 3 (1.4) | 0.88 |
| Total cholesterol, mg/dL (mean ± SD) | 237.2 ± 41.0 | 237.1 ± 41.8 | 0.97 |
| HDL cholesterol, mg/dL (mean ± SD) | 66.1 ± 17.3 | 61.2 ± 15.9 | <0.001 |
| LDL cholesterol, mg/dL (mean ± SD) | 130.5 ± 39.6 | 131.9 ± 39.0 | 0.68 |
| Triglycerides, mg/dL (mean ± SD) | 207.1 ± 83.0 | 217.0 ± 70.1 | 0.14 |
| Glucose, mg/dL (mean ± SD) | 74.2 ± 8.6 | 75.4 ± 7.2 | 0.09 |
| Insulin, mU/L (median, interquartile range) | 16.2 (11.1, 23.4) | 20.1 (13.5, 28.1) | <0.001 |
| HOMA-IR (median, interquartile range) | 2.93 (1.91, 4.33) | 3.69 (2.40, 5.48) | <0.001 |
In men and non-pregnant women, insulin resistance is associated with overweight and obesity, and therefore weight status may confound the relationship between insulin resistance and gallstone formation. In our subjects, HOMA-IR increased with pre-pregnancy overweight or obesity, compared to normal weight status (Table 2). In univariate analyses stratified by pre-pregnancy weight status, HOMA-IR was significantly greater in normal weight or overweight cases, compared to controls of comparable weight status (Table 2). In obese women (BMI≥30 kg/m2), HOMA-IR did not differ significantly between cases and controls.
Table 2.
Insulin resistance and incident gallbladder disease, stratified by pre-pregnancy body mass index
| HOMA-IR (median, interquartile range) | ||||
|---|---|---|---|---|
| Pre-pregnancy body mass index | All women (n=648) | No sludge or stones (n=443) | New sludge or stones (n=205) | p-value* |
| <25 kg/m2 | 2.64 (1.77, 3.69) | 2.56 (1.73, 3.60) | 3.00 (2.04, 3.83) | 0.06 |
| 25–29.9 kg/m2 | 3.87 (2.56, 5.42) | 3.49 (2.27, 5.03) | 4.83 (3.46, 6.17) | 0.001 |
| ≥30.0 kg/m2 | 5.49 (3.78, 7.47) | 5.56 (3.89, 7.80) | 4.82 (3.54, 7.02) | 0.30 |
Comparison of women with new sludge/stones vs. women without sludge/stones
Similarly, glucose and lipid levels are associated with insulin resistance, and therefore may confound the relationship between insulin resistance and gallbladder disease during pregnancy. Fasting glucose and triglycerides at 28 weeks gestation increased significantly, while LDL cholesterol levels decreased with increasing HOMA-IR (Table 3). There was a strong trend towards decreasing HDL cholesterol levels with increasing HOMA-IR, but no association of total cholesterol levels with HOMA-IR.
Table 3.
Insulin resistance, glucose and lipid levels at 27–29 weeks gestation
| HOMA-IR (quartiles) | |||||
|---|---|---|---|---|---|
| 0.70–2.08 | 2.09–3.18 | 3.19–4.84 | 4.85–18.98 | p-value for trend | |
| Glucose, mg/dL* | 68.8± 5.0 | 72.7± 5.2 | 74.8± 5.5 | 82.0± 9.7 | <0.001 |
| Triglyceride, mg/dL* | 193.1± 83.1 | 190.9± 61.9 | 213.8± 79.4 | 243.3± 79.7 | <0.0001 |
| Total cholesterol, mg/dL* | 235.1± 40.3 | 243.0± 38.4 | 234.7± 41.7 | 235.9± 44.1 | 0.64 |
| HDL cholesterol, mg/dL* | 66.1± 17.0 | 65.6± 15.3 | 62.5± 16.0 | 63.9± 19.3 | 0.06 |
| LDL cholesterol, mg/dL* | 130.4± 38.4 | 139.2± 35.7 | 129.9± 40.4 | 124.2± 41.8 | 0.02 |
All values are mean ± SD.
We developed logistic regression models to further characterize the relationship between gallstone formation, pre-pregnancy overweight or obesity, and insulin resistance (Table 4). We initially considered for inclusion all variables associated with case status with p<0.1. We also included other variables considered to be potential confounders, such as waist-hip ratio and physical activity, measured as MET-hrs expended weekly in the second and third trimesters. We first developed models examining either pre-pregnancy weight status or insulin resistance, but not both. Women were categorized into quartiles for degree of insulin resistance (measured by HOMA-IR).
Table 4.
Multivariate models of insulin resistance, body mass index, and gallstone formation
| Unadjusted odds ratio (95%CI) | Model 1 * | Model 2 † | Model 3 § | |
|---|---|---|---|---|
| adjusted odds ratio (95% CI) | adjusted odds ratio (95% CI) | adjusted odds ratio (95% CI) | ||
| HOMA-IR, quartiles | N/A | |||
| 0.70–2.08 | 1.00 | 1.00 | 1.00 | |
| 2.09–3.18 | 1.40 (0.83, 2.34) | 1.30 (0.78, 2.21) | 1.31 (0.77, 2.25) | |
| 3.19–4.84 | 2.88 (1.76, 4.71) | 2.40 (1.44, 3.98) | 2.48 (1.47, 4.18) | |
| 4.85–18.98 | 2.58 (1.58, 4.22) | 1.77 (1.03, 3.05) | 2.06 (0.17, 3.62) | |
| p-value | <0.001 | 0.005 | 0.004 | |
|
| ||||
| Pre-pregnancy body mass index, kg/m2 | N/A | |||
| <25.0 | 1.00 | 1.00 | 1.00 | |
| 25.0–29.9 | 1.30 (0.87, 1.95) | 1.08 (0.70, 1.66) | 1.12 (0.72, 1.75) | |
| ≥30.0 | 2.60 (1.66, 4.08) | 2.01 (1.23, 3.28) | 2.17 (1.29, 3.66) | |
| p-value | <0.001 | 0.01 | 0.01 | |
Adjusted for pre-pregnancy overweight or obesity
Adjusted for HOMA-IR
Includes both pre-pregnancy overweight/obesity and HOMA-IR. Also adjusted for Hispanic ethnicity, HDL cholesterol at 27–29 weeks, waist-hip ratio, and 2nd and 3rd trimester physical activity
In separate models, insulin resistance (Table 4, model 1) and pre-pregnancy overweight or obesity (Table 4, model 2) remained independent risk factors for gallstone incidence after adjustment for the other variable, although the strength of the association was attenuated. In a final multivariate model examining both HOMA-IR and pre-pregnancy weight status, insulin resistance remained a strong risk factor for gallstone formation, even after adjustment for pre-pregnancy overweight or obesity (Table 4, model 3). In this model, pre-pregnancy with status was still significantly associated with gallstone development after adjustment for insulin resistance, but the strength of the association was attenuated. Similar results were seen when HOMA-IR or pre-pregnancy BMI were entered into the model as a continuous, rather than categorical, variables, or when estradiol and progesterone levels were added to these models (data not shown). We have previously shown that estradiol and progesterone levels at 26–28 weeks gestation were not associated with new gallbladder sludge or stones in our population 10. In addition, Hispanic women may be genetically predisposed to cholesterol gallstone formation. Exclusion of such women from our analyses again did not significantly change these results (data not shown).
To further characterize the role of insulin resistance, we performed additional analyses stratified by pre-pregnancy weight status (Table 5). These analyses show that insulin resistance was a significant risk factor for gallstone development in normal weight or overweight women, but not in obese women. The interaction between pre-pregnancy weight status and insulin resistance in influencing risk for new gallbladder sludge or stones was of borderline significance (p=0.08).
Table 5.
Insulin resistance and gallstone development, stratified by pre-pregnancy body mass index
| Odds ratio (95% confidence interval)* | |||
|---|---|---|---|
| HOMA-IR, quartiles | BMI <25.0 kg/m2 (n=397) | BMI 25.0–29.9 kg/m2 (n=151) | BMI 30.0 kg/m2 (n=100) |
| 0.70–2.08 | 1.00 | 1.00 | 1.00 |
| 2.09–3.18 | 1.21 (0.66, 2.24) | 1.65 (0.33, 8.16) | 1.74 (0.21, 14.32) |
| 3.19–4.84 | 2.52 (1.34, 4.71) | 4.17 (0.96, 18.21) | 1.51 (0.22, 10.56) |
| 4.85–18.98 | 1.51 (0.69, 3.31) | 6.96 (1.59, 30.44) | 1.10 (0.17, 7.00) |
| p-value | 0.03 | 0.02 | 0.88 |
Adjusted for Hispanic ethnicity, HDL cholesterol at 27–29 weeks, waist-hip ratio, and 2nd and 3rd trimester physical activity
Discussion
We prospectively studied risk factors for incident gallbladder sludge and stones during pregnancy, and measured fasting serum glucose, lipids, and insulin during the period of gallstone formation. Our results are consistent with prior studies showing that fasting serum insulin, which may be used as a surrogate measure for insulin resistance, is a risk factor for prevalent gallstones 2, 14, 21–23. We found that women who formed gallbladder sludge or stones were significantly more insulin resistant, as measured with HOMA-IR. This association remained strong even after adjusting for possible confounding factors including pre-pregnancy BMI, lipid and glucose levels, waist-hip ratio, and physical activity during pregnancy. This association was strongest for women whose pre-pregnancy BMI was less than 30 kg/m2.
Prior studies have examined insulin levels and insulin resistance in subjects with prevalent gallstones 2, but not during the initial period of gallstone formation. For the majority of women in this study, gallbladder sludge or stones were first noted on the early 3rd trimester or postpartum ultrasounds. We measured serum insulin, glucose, and lipids at 27–29 weeks gestation, at a time when gallbladder sludge and stones were initially forming or had recently formed. Our study therefore extends previous findings and suggests that insulin resistance may be a pathogenic factor for gallstone formation. The effect of pre-pregnancy BMI on gallstone formation was attenuated after adjusting for insulin resistance, suggesting that insulin resistance may be part of the causal pathway linking obesity and gallstones.
The exact mechanisms whereby insulin resistance leads to gallstone formation are not clear. Cholesterol is the primary constituent of gallstones formed during pregnancy. Cholesterol gallstone formation requires several pathogenic factors, including supersaturation of hepatic bile with cholesterol and altered gallbladder motility. Hyperinsulinemia and insulin resistance may affect either of these factors. Hyperinsulinemia has direct effects on hepatic lipid metabolism, increasing cholesterol synthesis via activity of the hydroxyl-methylglutaryl coenzyme A reductase enzyme 24 and increasing hepatic uptake of LDL cholesterol 25. Insulin resistance is also associated with lower serum levels of HDL cholesterol, a known risk factor for prevalent gallstones 26. In one study, administration of insulin in diabetics increased biliary cholesterol saturation 27. Some, but not all, studies have shown greater degrees of biliary cholesterol saturation in patients with type II diabetes compared with controls 28, 29.
Insulin inhibits basal and cholecystokinin-stimulated gallbladder motility, and gallbladder dysmotility has been documented in patients with clinically diagnosed type II diabetes 30, 31. In animal models, non-obese, diabetic mice have diminished gallbladder contractility and rapid formation of cholesterol crystals 32, while gallbladder contractility correlates inversely with glucose and insulin levels in obese animals 33 Insulin resistance is associated with gallbladder dysmotility in non-obese, non-diabetic humans 34. Therefore, insulin resistance, even in the absence of obesity, may be lead to gallbladder sludge and stone formation, either by causing gallbladder dysmotility or by altering biliary lipid secretion.
Although our study strongly suggests that insulin resistance is a risk factor for gallstone formation, we cannot prove a direct mechanistic role from the analyses performed here. Insulin resistance may be a surrogate for other, undefined pathophysiologic mechanisms that lead to gallstone formation, rather than a direct underlying cause. We cannot account for all such potential pathophysiologic mechanisms in this analysis. For example, other, undefined abnormalities in lipid metabolism may lead to gallstone formation, and also lead independently to insulin resistance. We measured levels of insulin, glucose, estradiol, and progesterone at only one point in time, and levels earlier in pregnancy or changes in these levels may also be directly relevant. Therefore, our results should be viewed as hypothesis-generating, rather than hypothesis-testing. Further studies in animal models are needed to help clarify this potential relationship between insulin resistance and gallstone formation.
In summary, we have shown that insulin resistance is strongly associated with gallstone formation during pregnancy, independent of pre-pregnancy BMI. This association was strongest in women who were normal weight or overweight, but was not present in obese women. The effect of body weight was attenuated after adjusting for insulin resistance, suggesting that insulin resistance may represent an intermediate step linking body weight to gallstone formation. Although this study was performed in pregnant women, these results may also explain the association between obesity and gallstone disease that is well-documented in non-pregnant women and, to a lesser degree, in men. Further studies in non-pregnant populations are needed to confirm this possibility, and studies in animal models are needed to clarify the underlying mechanisms of this association.
Acknowledgments
Funding source: Supported by grants from the National Institutes of Health (DK46890 and CA 89218) and in part by the Department of Veterans Affairs. The study sponsors had no role in the study design in the collection, analysis, or interpretation of data.
We acknowledge the contributions to the study of Lorna Imbruglio, Nancy Allison, Andrea K. Herron, Lori J. Green, and Dianne Walkup.
Abbreviations
- HOMA-IR
Homeostasis model of insulin resistance
- BMI
Body mass index
- MET
Metabolic equivalent unit
Footnotes
Conflicts of Interest: No conflicts of interest exist.
Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
References
- 1.American Gastroenterological Association. The burden of gastrointestinal diseases. The American Gastroenterological Association; 2001. [Google Scholar]
- 2.Ruhl CE, Everhart JE. Association of diabetes, serum insulin, and C-peptide with gallbladder disease. Hepatology. 2000;31:299–303. doi: 10.1002/hep.510310206. [DOI] [PubMed] [Google Scholar]
- 3.Ruhl CE, Everhart JE. Relationship of serum leptin concentration and other measures of adiposity with gallbladder disease. Hepatology. 2001;34:877–83. doi: 10.1053/jhep.2001.29005. [DOI] [PubMed] [Google Scholar]
- 4.Everhart JE, Khare M, Hill M, Maurer KR. Prevalence and ethnic differences in gallbladder disease in the United States. Gastroenterology. 1999;117:632–639. doi: 10.1016/s0016-5085(99)70456-7. [DOI] [PubMed] [Google Scholar]
- 5.Barbara L, Sama C, Morselli-Labate AM, Taroni F, Rusticali AG, Festi D, Sapio C, Roda E, Banterle C, Puci A, Formentini F, Colasanti S, Nardin F. A population study on the prevalence of gallstone disease: the Sirmione study. Hepatology. 1987;7:913–919. doi: 10.1002/hep.1840070520. [DOI] [PubMed] [Google Scholar]
- 6.Rome Group for Epidemiology and Prevention of Cholelithiasis (GREPCO) The epidemiology of gallstone disease in Rome, Italy. Part II. Factors associated with the disease. Hepatology. 1988;8:907–913. [PubMed] [Google Scholar]
- 7.Maringhini A, Ciambra M, Baccelliere P, Raimondo M, Orlando A, Tine F, Grasso R, Randazzo MA, Barresi L, Gullo D, Musico M, Pagliaro L. Biliary sludge and gallstones in pregnancy: incidence, risk factors, and natural history. Ann Intern Med. 1993;119:116–120. doi: 10.7326/0003-4819-119-2-199307150-00004. [DOI] [PubMed] [Google Scholar]
- 8.Maringhini A, Marceno MP, Lanzarone F, Caltagirone M, Fusco G, DiCuonzo G, Cittadini E, Pagliaro L. Sludge and stones after pregnancy. J Hepatol. 1987;5:218–223. doi: 10.1016/s0168-8278(87)80576-7. [DOI] [PubMed] [Google Scholar]
- 9.Valdivieso V, Covarrubias C, Siegel F, Cruz F. Pregnancy and cholelithiasis: pathogenesis and natural course of gallstones diagnosed in early puerperium. Hepatology. 1993;17:1–4. [PubMed] [Google Scholar]
- 10.Ko CW, Beresford SA, Schulte SJ, Matsumoto AM, Lee SP. Incidence, natural history, and risk factors for biliary sludge and stones during pregnancy. Hepatology. 2005;41:359–365. doi: 10.1002/hep.20534. [DOI] [PubMed] [Google Scholar]
- 11.Lee SP, Maher K, Nicholls JF. Origin and fate of biliary sludge. Gastroenterology. 1988;94:170–176. doi: 10.1016/0016-5085(88)90626-9. [DOI] [PubMed] [Google Scholar]
- 12.Misciagna G, Guerra V, Di Leo A, Correale M, Trevisan M. Insulin and gall stones: a population case control study in southern Italy. Gut. 2000;47:144–7. doi: 10.1136/gut.47.1.144. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Scragg RKR, Clabert GD, Oliver JR. Plasma lipids and insulin in gallstone disease: a case-control study. Br Med J. 1984;289:521–525. doi: 10.1136/bmj.289.6444.521. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Kono S, Kochi S, Ohyama S, Wakisaka A. Gallstones, serum lipids, and glucose tolerance among male officials of Self-Defense Forces in Japan. Dig Dis Sci. 1988;33:839–44. doi: 10.1007/BF01550973. [DOI] [PubMed] [Google Scholar]
- 15.Haffner SM, Diehl AK, Mitchell BD, Stern MP, Hazuda HP. Increased prevalence of clinical gallbladder disease in subjects with non-insulin-dependent diabetes mellitus. Am J Epidemiol. 1990;132:327–35. doi: 10.1093/oxfordjournals.aje.a115662. [DOI] [PubMed] [Google Scholar]
- 16.Laakso M, Suhonen M, Julkunen R, Pyorala K. Plasma insulin, serum lipids and lipoproteins in gall stone disease in non-insulin dependent diabetic subjects: a case control study. Gut. 1990;31:344–7. doi: 10.1136/gut.31.3.344. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Jorgensen T. Gall stones in a Danish population. Relation to weight, physical activity, smoking, coffee consumption, and diabetes mellitus. Gut. 1989;30:528–34. doi: 10.1136/gut.30.4.528. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.Matthews DR, Hosker JP, Rudenski AS, Naylor BA, Treacher DF, Turner RC. Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia. 1985;28:412–9. doi: 10.1007/BF00280883. [DOI] [PubMed] [Google Scholar]
- 19.Jacobs DR, Jr, Ainsworth BE, Hartman TJ, Leon AS. A simultaneous evaluation of 10 commonly used physical activity questionnaires. Med Sci Sports Exerc. 1993;25:81–91. doi: 10.1249/00005768-199301000-00012. [DOI] [PubMed] [Google Scholar]
- 20.Ainsworth BE, Haskell WL, Whitt MC, Irwin ML, Swartz AM, Strath SJ, O’Brien WL, Bassett DR, Jr, Schmitz KH, Emplaincourt PO, Jacobs DR, Jr, Leon AS. Compendium of physical activities: an update of activity codes and MET intensities. Med Sci Sports Exerc. 2000;32:S498–504. doi: 10.1097/00005768-200009001-00009. [DOI] [PubMed] [Google Scholar]
- 21.Kono S, Shinchi K, Ikeda N, Yanai F, Imanishi K. Prevalence of gallstone disease in relation to smoking, alcohol use, obesity, and glucose tolerance: a study of self-defense officials in Japan. Am J Epidemiol. 1992;136:787–94. doi: 10.1093/aje/136.7.787. [DOI] [PubMed] [Google Scholar]
- 22.Maurer KR, Knowles JE, Everhart WD, Shawker TH, Roth HP. Risk factors for gallstone disease in the Hispanic populations of the United States. Am J Epidemiol. 1990;96:487–492. doi: 10.1093/oxfordjournals.aje.a115574. [DOI] [PubMed] [Google Scholar]
- 23.De Santis A, Attili AF, Ginanni Corradini S, Scafato E, Cantagalli A, De Luca C, Pinto G, Lisi D, Capocaccia L. Gallstones and diabetes: a case-control study in a free-living population sample. Hepatology. 1997;25:787–90. doi: 10.1002/hep.510250401. [DOI] [PubMed] [Google Scholar]
- 24.Ness GC, Zhao Z, Wiggins L. Insulin and glucagon modulate hepatic 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity by affecting immunoreactive protein levels. J Biol Chem. 1994;269:29168–72. [PubMed] [Google Scholar]
- 25.Chait A, Bierman EL, Albers JJ. Low-density lipoprotein receptor activity in cultured human skin fibroblasts. Mechanism of insulin-induced stimulation. J Clin Invest. 1979;64:1309–19. doi: 10.1172/JCI109587. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 26.Petitti DB, Friedman GD, Klatsky AL. Association of a history of gallbladder disease with a reduced concentration of high-density-lipoprotein cholesterol. N Engl J Med. 1981;304:1396–1398. doi: 10.1056/NEJM198106043042305. [DOI] [PubMed] [Google Scholar]
- 27.Bennion LJ, Grundy SM. Effects of diabetes mellitus on cholesterol metabolism in man. N Engl J Med. 1977;296:1365–71. doi: 10.1056/NEJM197706162962401. [DOI] [PubMed] [Google Scholar]
- 28.de Leon MP, Ferenderes R, Carulli N. Bile lipid composition and bile acid pool size in diabetes. Am J Dig Dis. 1978;23:710–6. doi: 10.1007/BF01072357. [DOI] [PubMed] [Google Scholar]
- 29.Haber GB, Heaton KW. Lipid composition of bile in diabetics and obesity-matched controls. Gut. 1979;20:518–22. doi: 10.1136/gut.20.6.518. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 30.Gielkens HA, Lam WF, Coenraad M, Frolich M, van Oostayen JA, Lamers CB, Masclee AA. Effect of insulin on basal and cholecystokinin-stimulated gallbladder motility in humans. J Hepatol. 1998;28:595–602. doi: 10.1016/s0168-8278(98)80282-1. [DOI] [PubMed] [Google Scholar]
- 31.Hahm JS, Park JY, Park KG, Ahn YH, Lee MH, Park KN. Gallbladder motility in diabetes mellitus using real time ultrasonography. Am J Gastroenterol. 1996;91:2391–4. [PubMed] [Google Scholar]
- 32.Graewin SJ, Kiely JM, Lee KH, Svatek CL, Nakeeb A, Pitt HA. Nonobese diabetic mice have diminished gallbladder motility and shortened crystal observation time. J Gastrointest Surg. 2004;8:824–9. doi: 10.1016/j.gassur.2004.06.014. [DOI] [PubMed] [Google Scholar]
- 33.Tran KQ, Goldblatt MI, Swartz-Basile DA, Svatek C, Nakeeb A, Pitt HA. Diabetes and hyperlipidemia correlate with gallbladder contractility in leptin-related murine obesity. J Gastrointest Surg. 2003;7:857–62. doi: 10.1007/s11605-003-0030-z. [DOI] [PubMed] [Google Scholar]
- 34.Nakeeb A, Comuzzie AG, Al-Azzawi H, Sonnenberg GE, Kissebah AH, Pitt HA. Insulin resistance causes human gallbladder dysmotility. J Gastrointest Surg. 2006;10:940–8. doi: 10.1016/j.gassur.2006.04.005. [DOI] [PubMed] [Google Scholar]