Vitamin D status and biomarkers of inflammation in runners
Kentz S Willis1, Derek T Smith2, Kenneth S Broughton3, D Enette Larson-Meyer2,3
1Extension, 2Division of Kinesiology and Health, 3Department of Family and Consumer Sciences (Human Nutrition), University of Wyoming, Laramie, WY, USA
Background and purpose: The extra-skeletal functions of vitamin D – including its role in inflammatory modulation – are now well recognized but have not yet been investigated in an athletic population. Thus, the purpose of this study was to investigate the relationship between vitamin D status and pro- and anti-inflammatory cytokines (as markers of inflammation and immune system function) in endurance athletes.
Patients and methods: We analyzed fasting blood samples from 19 healthy, endurance-trained male and female runners (following a standardized diet and exercise regimen) for vitamin D status (serum 25-hydroxyvitamin D [25(OH)D)] and specific plasma cytokine concentrations (tumor necrosis factor alpha [TNF-α], interferon-gamma [IFN-γ], interleukin [IL]-4, and IL-10). Serum/plasma concentrations were log-transformed and simple regression analysis was used to determine significant associations between 25(OH)D and cytokine concentrations.
Results: Forty-two percent of participants had insufficient vitamin D status [25(OH)D < 32 ng/mL], whereas 11% were deficient [25(OH)D , 20 ng/mL]. TNF-α and IL-4 were variable, ranging from 2.9 to 36.4 pg/mL and 0 to 252.1 pg/mL, respectively. Concentrations of IFN-γ and IL-10 were minimal, with means of 6.7 ± 7.0 pg/mL and 4.8 ± 5.1 pg/mL, respectively. Regression analysis revealed a significant inverse association between 25(OH)D and TNF-α concentrations (R2 = 56.5, P < 0.001) but not between 25(OH)D and the remaining cytokines, IFN-γ, IL-4, and IL-10 (P = 0.477, 0.694, and 0.673, respectively).
Conclusion: These results call further attention to the epidemic of vitamin D insufficiency, even in outdoor athletes, and support a possible link between decreased vitamin D status and one particular marker of inflammation. Future investigations are necessary to determine whether increased inflammation in athletes with reduced vitamin D status could increase risk for inflammation-related injury.
Keywords: health, exercise training, tumor necrosis factor alpha, cytokines, injury risk
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