Abstract
Background and AimRecent studies revealed a link between hypovitaminosis D3 and the risk for hyperglycemia. Further mechanistic and interventional investigations suggested a common reason for both conditions rather than a causal relationship. Exposure to sunlight is the most relevant source of vitamin D3 (25(OH)D), whereas adipose tissue is able to store relevant amounts of the lipophilic vitamin. Since running/bicycling leads to increased out-door time and alters physiological response mechanisms, it can be hypothesized that the correlation between hypovitaminosis D3 and hyperglycemia might be disturbed in outdoor athletes.Methods47 elderly marathoners/bicyclists and 47 age/sex matched controls were studied in a longitudinal setting at baseline and after three years. HbA1c as a surrogate for (pre-)diabetic states was quantified via HPLC, 25(OH)D levels were measured by means of chemiluminescent assays. Physical performance was assessed by ergometry.ResultsWhen adjusted for seasonal variations, 25(OH)D was significantly higher in athletes than in controls. 25(OH)D levels inversely correlated with triglycerides in both groups, whereas only in controls an association between high BMI or low physical performance with hypovitaminosis D3 had been found. Likewise, the presence of hypovitaminosis D3 at baseline successfully predicted hyperglycemia at the follow up examinations within the control group (AUC = 0.85, 95% CI [0.74, 0.96], p < .001, statistically independent from BMI), but not in athletes.ConclusionOur data suggest that mechanisms of HbA1c elevation might differ between athletes and controls. Thus, intense physical activity must be taken into account as a potential pre-analytic confounder when it is aimed to predict metabolic risk by vitamin D3 levels.
Highlights
During the last decade, an inverse relationship between peripheral 25(OH)D levels and insulin resistance has been clearly established
When adjusted for seasonal variations, 25(OH)D was significantly higher in athletes than in controls. 25(OH)D levels inversely correlated with triglycerides in both groups, whereas only in controls an association between high body mass index (BMI) or low physical performance with hypovitaminosis D3 had been found
The presence of hypovitaminosis D3 at baseline successfully predicted hyperglycemia at the follow up examinations within the control group (AUC = 0.85, 95% CI [0.74, 0.96], p < .001, statistically independent from BMI), but not in athletes
Summary
An inverse relationship between peripheral 25(OH)D (vitamin D3) levels and insulin resistance has been clearly established. The underlying mechanisms are not yet fully elucidated and it appears that 25(OH)D deficiency might be rather a result than a cause of metabolic dysregulation [1] This assumption is supported by recent meta-analyses that could not identify a considerable therapeutic effect of cholecalciferol supplementation on metabolic diseases [2,3]. Circulating levels of vitamin D derivates could be very valuable for estimating patients’ individual risks In this regard, Kabadi et al reported that the interaction between serum 25(OH)D and body mass index (BMI) accounts for 47% of the increased odds for developing an insulin resistance [4]. Clemente-Postigo and coworkers described significantly lower levels of 25(OH)D in prediabetic and diabetic patients when compared to individuals without a pathological glycemic status This effect did not depend on BMI. Since running/bicycling leads to increased out-door time and alters physiological response mechanisms, it can be hypothesized that the correlation between hypovitaminosis D3 and hyperglycemia might be disturbed in outdoor athletes
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