Effect of vitamin D supplementation on glycemic control in patients with type 2 diabetes: a systematic review of interventional studies

Abstract

BackgroundDiabetes and vitamin D deficiency are global epidemics. Researchers have long been exploring the role of potentially modifiable factors to manage type 2 diabetes. We conducted a systematic review of prospective studies and randomized controlled trials that involved vitamin D supplementation and specifically intended to study glycemic outcomes related to type 2 diabetes.MethodsTwo authors independently searched Medline and PubMed for longitudinal studies that had assessed the effect of vitamin D supplements on glycemic control, insulin resistance and beta-cell dysfunction in patients with diabetes.ResultsSeventeen randomized control trials and seven longitudinal studies with a minimum follow-up of one month were included.Results of the various short-term studies (follow up ≤ 3 months) suggested that vitamin D supplementation had a positive impact on glycemic control and metabolic parameters such as insulin resistance and beta cell dysfunction. However, the evidence was weak due to the low methodological quality of the studies. There was no significant effect on HbA1c, beta cell function and insulin resistance in the long-term studies (follow up > 3 months). There existed heterogeneity in the methodology of the studies, inclusion criteria, mode of supplementation of vitamin D and the duration of follow up.ConclusionsCurrent evidence based on randomized controlled trials and longitudinal studies do not support the notion that vitamin D supplementation can improve hyperglycemia, beta cell secretion or insulin sensitivity in patients with type 2 diabetes. Large-scale trials with proper study design, optimal vitamin D supplementation and longer follow up need to be conducted.

Effects of vitamin D supplementation on glycated haemoglobin and fasting glucose levels in hypertensive patients: a randomized controlled trial

“…[48][49][50][51][52][53][54][55] In recent meta-analyses and systematic reviews, this led to the notion that there is currently no evidence to support a routine correction of vitamin D insufficiency in patients with diabetes mellitus or glucose intolerance. 7,8,18,19,56,57 Nevertheless, the heterogeneity between the different trials, especially with regard to dose, treatment duration and ethnicity, leaves the possibility that there are certain subgroups of patients who might benefit from vitamin D supplementation. 7,8,18,19,56,57 The present findings, if confirmed in other larger trials, may help to define subgroups of patients who might benefit from vitamin D supplementation with regard to control of glucose homeostasis.…”

“…7,8,18,19,56,57 Nevertheless, the heterogeneity between the different trials, especially with regard to dose, treatment duration and ethnicity, leaves the possibility that there are certain subgroups of patients who might benefit from vitamin D supplementation. 7,8,18,19,56,57 The present findings, if confirmed in other larger trials, may help to define subgroups of patients who might benefit from vitamin D supplementation with regard to control of glucose homeostasis. Mechanistic evidence has shown that vitamin D is required for normal phase 1 and 2 insulin responses to hyperglycaemia.…”

“…Nevertheless, it should be acknowledged that the majority of trials failed to demonstrate a consistent and clinically meaningful benefit of vitamin D treatment on glycaemic control in diabetes mellitus, glucose intolerance or in other cohorts . In recent meta‐analyses and systematic reviews, this led to the notion that there is currently no evidence to support a routine correction of vitamin D insufficiency in patients with diabetes mellitus or glucose intolerance . Nevertheless, the heterogeneity between the different trials, especially with regard to dose, treatment duration and ethnicity leave the possibility that there are certain subgroups of patients who might benefit from vitamin D supplementation .…”

Effect of vitamin D supplementation on measures of arterial stiffness: a systematic review and meta‐analysis of randomized controlled trials

“…Indeed, the optimal vitamin D dosing protocol in terms of concentration and frequency is unclear . This is a consistent technical problem in study design, as many interventional studies that are grounded in epidemiological evidence suggesting low vitamin D is associated with an outcome, show no effect for vitamin D supplementation . However, attempts to overcome this with high‐dose vitamin D supplementation may be harmful .…”

The effect of vitamin D supplementation on glucose metabolism in type 2 diabetes mellitus: A systematic review and meta-analysis of intervention studies

“…Indeed, previous studies have reported glycemic benefits and improvements in beta cell function among vitamin D deficient adults upon vitamin D supplementation. 11,12 Since the previously published reviews on this topic, 8,9 we found 11 additional eligible studies; by updating the search and using a more comprehensive set of search terms compared to the prior reviews, we found six new RCTs completed since the previous review and five older studies not included in previous systematic reviews that met the inclusion criteria in our review.…”