Aim Besides its relation to mortality, cardiac autonomic function has been shown to provide information about athletic performance and exercise tolerance. The relationship between cardiac autonomic dysfunction and vitamin D deficiency is not known in healthy athletes although it has been well depicted in healthy subjects. Therefore, we asked a question if serum vitamin D levels plays a role to maintain cardiac autonomic function in athletes.

Methods A total number of 89 healthy volunteers (55 athletes and 33 sedentary subjects)

were participated in this randomised case-control study. After measuring initial serum 25(OH) vitamin D concentrations, all participants underwent a submaximal exercise stress testing by using Bruce protocol. After reaching 85% of the age-predicted heart rate (220-Age), treadmill exercise has been stopped and heart rates were obtained after first, second and third minutes of recovery. Heart-rate recovery indexes (HRR1, HRR2 and HRR3) were calculated by subtracting first-, second-, and third-minutes of heart rates from the pike heart rate reached during the exercise test (ie 85% of Max HR).

Results There were no correlations between serum vitamin D levels and any of the HRR indexes neither in athletes nor in control subjects. On the other hand, when groups were divided to two based on their vitamin D levels, HRR2 index was significantly lower in low vitamin D group (<15 ng/ml) compare to high vitamin D group only in control subjects.

Conclusion These results suggest that unlike sedentary control group, the cardiac autonomic function was not affected by the vitamin D deficiency in athletes. It can be speculated that the positive effect of regular exercise on parasymphathetic and sympathetic regulation may play a role on these findings.