Relationship Between Vitamin D And Nonalcoholic Fatty Liver Disease

Objective Now vitamin D is considered as a kind of steroid hormones. Besides its well-known function of the classic regulating the metabolism of calcium and phosphorus, it also has anti-inflammatory, anti-infection and immunity adjustment effects. It is known to all that vitamin D deficiency may play a role in the occurrence and development process of a variety of disease. However, in clinical study, it still remains disputable whether the association between hypovitaminosis D and the development of nonalcoholic fatty liver disease(NAFLD) exists. Some studies have linked vitamin D deficiency to NAFLD, while others have not. The aim of this study was to explore the correlation of vitamin D deficiency and NAFLD by a case-control study.Methods A total of 1,150 subjects admitted to our hospital between April and June 2013 participated in the study. Basic conditions of individuals were surveyed by a standard questionnaire, including sex, age, nationality, education, occupation, smoking history, drinking history, medication history, NAFLD developing histroy and other metabolic disease history. Height, weight, waist circumference, heart rate, blood pressure and other indicators were also collected by physical examinations. Body mass index was calculated by dividing weight in kilograms, by height in meter squared. Venous blood was drawn in the morning with more than 8 hours on an empty stomach. Serum albumin, total bilirubin, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, glutamyltransferase, lactate dehydrogenase, urea nitrogen, creatinine, uric acid, total cholesterol, triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, fasting plasma glucose, serum calcium and phosphorus were measured. Enzyme-linked immunosorbent assay was used to determine hepatitis B virus surface antigenand hepatitis C antibody. Abdominal ultrasound examination was used to assess the severity of the fatty liver disease by professional radiologists who were blinded to the aims of the study using the B-mode ultrasonic equipment. The ultrasonographically detected NAFLD patients were categorized as mild NAFLD group, moderate NAFLD group and severe NAFLD group. According to the inclusion and exclusion criteria, eventually 104 cases and 98 age and sex matched healthy controls were recruited in this case-control study. Radioimmunoassay was used to analyze the concentration of 25(OH)D in serum. Statistical methods used to analyze the relationship between 25(OH)D concentration and NAFLD included two independent sampling t analysis, ANOVA analysis, logistic regression analysis.Results These two groups had statistically significant difference(P <0.001 or P < 0.05) in BMI, waist circumference, systolic and diastolic blood pressure, liver enzymes, uric acid, fasting plasma glucose and a more atherogenic lipid profile. In contrast, the NAFLD group and the control group had no statistically significant difference in age, sex, AKP, Cr, serum 25(OH)D concentration(20.87±6.73 vs. 21.63±8.22 ng/ml, P=0.474), calcium or phosphorus concentrations(P>0.05 for all). And these two groups had statistically significant difference in serum 25(OH)D <15ng/ml or ≥15ng/ml(P>0.05 for all). However, in stratification analysis by age, sex and BMI, NAFLD patients with age less than or equal to 30 had lower serum 25(OH) D levels(16.85±7.56 vs. 22.23±5.78ng/ml, P=0.04) and an increased odds of 25(OH)D deficiency(<15ng/ml) than people in the corresponding control group(χ2=6.679, OR=13.71, 95% C.I:1.38-136.21, P=0.025). NAFLD patients with BMI less than or equal to 25 also had an increased odds of 25(OH)D deficiency(<15ng/ml) than people in the corresponding control group(χ2=3.734, OR=4.97, 95% C.I:2.27-10.89, P<0.001). However, the odds of 25(OH)D deficiency had no statistical difference in cases and control groups with age between 30-50 years or older than 50 years(P>0.05 for all). The odds of 25(OH)D deficiency also had no statistical difference in the two groups with sex and BMI>25kg/m2 stratification(P>0.05 for all). After stratifying the study sample according to serum 25(OH)D quartiles, we observed all groups had no statistical difference in parameters, such as age, sex, BMI, ALT, AST, AKP, GGT, LDH, UA, Cr, TCH, LDL-C(P>0.05 for all). Moreover, there were no significantly difference in the incidence of NAFLD among groups(P>0.05). However, we found that significantly lower values of high-density lipoprotein cholesterol(P<0.001) in the lowest 25(OH)D quartile, as compared to other quartiles. In the hightest 25(OH)D quartile, the subjects had the lower levels of fasting plasma glucose(P=0.02). However, the results also showed that the values of the hightest triglyceride levels were presented to the hightest 25(OH)D quartile(P=0.02).The results showed that there was no significant difference in the serum 25(OH)D concentrations in different degree of NAFLD(F=0.419, P=0.740). The odds of 25(OH)D deficiency(<15ng/ml) or the odds of 25(OH)D<30ng/ml had no statistical difference in all groups(χ2=3.844, P=0.279; χ2=2.143, P=0.516, respectively). Multivariable logistic regression analysis showed that the two variables, BMI and TG, were risk factors for NAFLD in the overall samples. In a subgroup of subjects with normal BMI(<=25kg/m2), logistic regression analysis showed that vitamin D and NAFLD were related to each other by adjusting for multiple compounding variables including age, sex, TG, TCH, HDL-C, LDL-C, FPG and UA(OR=1.16, 95%C.I:1.03-1.30, P=0.032). Whereas UA, TCH and age were significantly associated with NAFLD in the analysis of the degree of ultrasonographically detected NAFLD.Conclusions In our study populations, compared with matched controls, NAFLD for patients <=30 years old or normal BMI(<=25kg/m2) had an increased odds of 25(OH)D deficiency, suggesting that vitamin D deficiency might play a relatively important role in younger NAFLD patients and/or in NAFLD patients with normal BMI.