***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: This article introduces the approach of GRADE to rating  quality of evidence .  GRADE specifies four categories-high , moderate , low , and very low-that are applied to a body of evidence , not to individual studies . In the context of a systematic review , quality reflects our confidence that the estimates of the effect are correct . In the context of recommendations , quality reflects our confidence that the effect estimates are adequate to support a particular recommendation . R and omized trials begin as high- quality evidence , observational studies as low quality . " Quality " as used in GRADE means more than risk of bias and so may also be compromised by imprecision , inconsistency , indirectness of study results , and publication bias . In addition , several factors can increase our confidence in an estimate of effect . GRADE provides a systematic approach for considering and reporting each of these factors . GRADE separates the process of assessing quality of evidence from the process of making recommendations . Judgments about the strength of a recommendation depend on more than just the quality of evidence The Institute of Medicine Committee to Review Dietary Reference Intakes for Calcium and Vitamin D comprehensively review ed the evidence for both skeletal and nonskeletal health outcomes and concluded that a causal role of calcium and vitamin D in skeletal health provided the necessary basis for the 2011 Estimated Average Requirement ( EAR ) and Recommended Dietary Allowance ( RDA ) for ages older than 1 year . For nonskeletal outcomes , including cancer , cardiovascular disease , diabetes , infections , and autoimmune disorders , r and omized clinical trials were sparse , and evidence was inconsistent , inconclusive as to causality , and insufficient for Dietary Reference Intake ( DRI ) development . The EAR and RDA for calcium range from 500 to 1,100 and 700 to 1,300 mg daily , respectively , for ages 1 year and older . For vitamin D ( assuming minimal sun exposure ) , the EAR is 400 IU/day for ages older than 1 year and the RDA is 600 IU/day for ages 1 to 70 years and 800 IU/day for 71 years and older , corresponding to serum 25-hydroxyvitamin D ( 25OHD ) levels of 16 ng/mL ( 40 nmol/L ) for EARs and 20 ng/mL ( 50 nmol/L ) or more for RDAs . Prevalence of vitamin D inadequacy in North America has been overestimated based on serum 25OHD levels corresponding to the EAR and RDA . Higher serum 25OHD levels were not consistently associated with greater benefit , and for some outcomes U-shaped associations with risks at both low and high levels were observed . The Tolerable Upper Intake Level for calcium ranges from 1,000 to 3,000 mg daily , based on calcium excretion or kidney stone formation , and from 1,000 to 4,000 IU daily for vitamin D , based on hypercalcemia adjusted for uncertainty result ing from emerging risk relationships . Urgently needed are evidence -based guidelines to interpret serum 25OHD levels relative to vitamin D status and intervention Background : Low 25-hydroxyvitamin D [ 25(OH)D ] levels are commonly found in HIV – hepatitis C virus ( HCV ) coinfected patients and are associated with liver fibrosis . No association between 25(OH)D levels and response to pegylated interferon & agr;-2a/2b plus ribavirin ( PEGIFN + RBV ) has yet been reported for HIV – HCV coinfected patients . Design : Epidemiological characteristics , HIV and HCV infection parameters , liver biopsies , as well as data on virologic response was available in 65 patients who received chronic hepatitis C ( CHC ) therapy with PEGIFN + RBV within a prospect i ve trial . 25(OH)D levels were retrospectively assessed using stored screening serum sample s obtained within 35 days prior to CHC treatment . Methods : According to their 25(OH)D levels , patients were assigned to the normal ( > 30 ng/ml ; D-NORM ) , the insufficiency ( 10–30 ng/ml ; D-INSUFF ) , or the deficiency ( < 10 ng/ml ; D-DEF ) group . HCV-GT 1/4 , high HCV-RNA load ( > 6 × 105 IU/ml ) , advanced liver fibrosis ( METAVIR F3/F4 ) , and IL28B rs12979860non-C/C were considered as established risk factors for treatment failure in HIV – HCV coinfected patients . Results : Thirty-seven ( 57 % ) and 15 ( 23 % ) patients presented with D-INSUFF and D-DEF , respectively , whereas only 13 ( 20 % ) patients had normal 25(OH)D levels . Substantial differences in cEVR ( D-NORM 92 % vs. D-INSUFF 68 % vs. D-DEF 47 % ; P = 0.008 ) and SVR ( D-NORM 85 % vs. D-INSUFF 60 % vs. D-DEF 40 % ; P = 0.029 ) rates were observed between 25(OH)D subgroups . Especially in difficult-to-treat patients with multiple ( three to four ) established risk factors , low 25(OH)D levels were clearly associated with lower rates of SVR [ patients without 25(OH)D deficiency 52 % vs. D-DEF 0 % ; P = 0.012 ] . Conclusion : Low 25(OH)D levels may impair virologic response to PEGIFN + RBV therapy , especially in difficult-to-treat patients  . Vitamin D supplementation should be considered and evaluated prospect ively in HIV – HCV coinfected patients receiving CHC treatment 
    Output:
    
CONCLUSION Low vitamin D status is common in chronic Hepatitis C patients and is associated with advanced liver fibrosis