Is there a relationship between serum vitamin D level and cardiac autonomic function in athletes?

BACKGROUND: Besides mortality, cardiac autonomic function is also associated with athletic performance and exercise tolerance. The relationship between cardiac autonomic dysfunction and vitamin D deficiency in healthy athletes is unknown, although it has been well described in healthy participants. METHODS: Eighty-nine healthy volunteers (56 athletes and 33 sedentary control) participated in this randomized case-control study. Heart rate recovery indexes (HRR1, HRR2, and HRR3) were calculated by subtracting the one-, two-, and three-minute recovery heart rates from the peak rate during the exercise test (i.e., 85% of HRmax). RESULTS: There were no correlations between serum vitamin D levels and any of the HRR indexes in either group. However, when the groups were divided according to their vitamin D levels, the HRR2 index in the control group was significantly lower in the low vitamin D group (<15 ng/mL) than in the high vitamin D group. HRR3 was found significantly higher in athletes (median 67.5 vs. 55, P=0.001) compared with the control subjects. CONCLUSIONS: These results suggest that the cardiac autonomic function was not affected by vitamin D deficiency in athletes, unlike in the sedentary control group. The positive effect of regular exercise on parasympathetic and sympathetic regulation may play a role in these findings.