In conclusion , this review supports the hypothesis that hypovitaminosis D is associated with adverse outcomes after diverse surgical procedures .
The importance of vitamin D for musculoskeletal health has long been recognized , and awareness of significant extra-skeletal effects in health and disease is rapidly emerging .
Although it has been possible for many decades to quantify serum markers of vitamin D deficiency , and to correct deficiency at low cost and with high safety , the influence of vitamin D status on post-surgical outcomes has only recently been identified as a research topic of interest .
To the present , these data have not been the subject matter of formal review .
Accordingly , we conducted a systematic review to assess the association between perioperative vitamin D status and outcomes after surgery .
GRADE guidelines: 3. Rating the quality of evidence.
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
In conclusion , this review supports the hypothesis that hypovitaminosis D is associated with adverse outcomes after diverse surgical procedures .
The importance of vitamin D for musculoskeletal health has long been recognized , and awareness of significant extra-skeletal effects in health and disease is rapidly emerging .
Although it has been possible for many decades to quantify serum markers of vitamin D deficiency , and to correct deficiency at low cost and with high safety , the influence of vitamin D status on post-surgical outcomes has only recently been identified as a research topic of interest .
To the present , these data have not been the subject matter of formal review .
Accordingly , we conducted a systematic review to assess the association between perioperative vitamin D status and outcomes after surgery .