Background: Exercise-induced (EI) symptoms may be associated with bronchospasm (EI-B), or laryngospasm, that is a paradoxical VC adduction (VCD) mimicking asthma. We previously found that vitamin D deficiency (Ddef) favours the occurrence of VCD during hyperventilation test (HV), particularly in hypocapnic conditions. We evaluated the occurrence of EI-B and EI-VCD during HV in relationship with Ddef, in 37 non smoking young athletes (24 males, 13 females, age: 13-25 years). Methods: Each subject underwent HV (5 runs of one minute) either in isocapnia (HViso, obtained breathing CO2 enriched air) or in hypocapnia (HVhypo, obtained breathing normal air) in randomized order, one week apart. Exhaled CO2 pressure was controlled breath by breath by a capnograph. A 10% decrease in FEV1 was used as EI-B marker, a 25% decrease in MIF50 as EI-VCD marker. Results: Sixteen subjects (43%) were atopic, 6 (16%) reported past diagnosis of asthma. No subject was assuming drugs or had suffered from respiratory infections in the last month. All subjects had normal lung function tests. With HViso 10 subjects had EI-B and 12 had EI-VCD. With HVhypo 8 subjects had EI-B and 15 EI-VCD. Eighteen subiects (49%) had Ddef (serum 25-hydroxycholecalcipherol < 25 ng/mL). Serum levels of vitamin D were significantly lower in athletes with than in those without EI-VCD, either with HViso (19.1 +/- 1.8 vs 25.7 +/- 1.5 ng/mL; P = 0.013) or with HVhypo (20.2 +/- 1.9 vs 26.2 +/- 1.8 ng/mL; P = 0.029). No influence of vitamin D on EI-B could be demonstrated. Vitamin D levels were significantly related to the decrease in MIF50 (as % of baseline) during the test (HViso: r = 0.41; P < 0.015 and HVipo: r = 0.42; P = 0.017). Conclusions: Our young athletes had a high prevalence of paradoxical vocal cord adduction during HV, which was strongly associated to Ddef. The high prevalence of Ddef was expected, since the study was conducted during winter in a town located beyond 45[degrees] latitude. Vitamin D deficiency may favour laryngospasm by decreasing calcium availability, ATP production and Ca-ATPase pump activity in the striate muscle cell, with consequent tetanic contraction and delayed relaxation. The fact that alkalosis worsens hypocalcemia accounts for the higher prevalence of laryngospasm observed during HVhypo.
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