Studies monitoring vitamin D status in athletes are seldom conducted for a period of 12 months or longer, thereby lacking insight into seasonal fluctuations. The objective of the cur-rent study was to identify seasonal changes in total 25-hydroxyvitamin D (25(OH)D) concen-tration throughout the year. Fifty-two, mainly Caucasian athletes with a sufficient 25(OH)D concentration (>75 nmol/L) in June were included in this study. Serum 25(OH)D concentra-tion was measured every three months (June, September, December, March, June). Addition-ally, vitamin D intake and sun exposure were assessed by questionnaires at the same time points. Highest total 25(OH)D concentrations were found at the end of summer (113±26 nmol/L), whereas lowest concentrations were observed at the end of winter (78±30 nmol/L). Although all athletes had a sufficient 25(OH)D concentration at the start of the study, nearly 20% of the athletes were deficient (<50 nmol/L) in late winter.
Annual rhythms in humans have been described for a limited number of behavioral and physiological parameters. The aim of this study was to investigate time-of-year variations in late arrivals, sick leaves, dismissals from class (attendance), and grades (performance). Data were collected in Dutch high school students across 4 academic years (indicators of attendance in about 1700 students; grades in about 200 students). Absenteeism showed a seasonal variation, with a peak in winter, which was more strongly associated with photoperiod (number of hours of daylight) compared with other factors assessed (e.g., weather conditions). Grades also varied with time of year, albeit differently across the 4 years. The observed time-of-year variation in the number of sick leaves was in accordance with the literature on the seasonality of infectious diseases (e.g., influenza usually breaks out in winter). The winter peak in late arrivals was unexpected and requires more research. Our findings could be relevant for a seasonal adaptation of school schedules and working environments (e.g., later school and work hours in winter, especially at higher latitudes where seasonal differences in photoperiod are more pronounced).
The aim of this study was to prospectively monitor sport-specific performance and assess the stress-recovery balance in overreached (OR) soccer players and controls. During two competitive seasons, 94 players participated in the study. The stress-recovery balance (RESTQ-Sport) and sport-specific performance (Interval Shuttle Run Test) were assessed monthly. Seven players with performance decrement of at least a month were classified as OR. Stress and recovery measures were assessed between groups (OR vs healthy players) and at different times within the OR group. An unfavorable total recovery score appeared 2 months before diagnosis when compared with the reference values of the healthy group established at the start of the season (P=0.009) and also over the two seasons (P=0.028). The scales Emotional Stress (P=0.044), Physical Recovery (P=0.009), General Well-being (P=0.001) and Sleep Quality (P=0.045) were sensitive to OR compared with the average of the healthy group over the two seasons. Finally, Fatigue and Being in Shape demonstrated the largest changes in stress and recovery within the OR players (effect size=1.14 and 1.50). The longitudinal monitoring of performance and changes in stress and recovery may be useful for the detection of OR in its earliest stage. The information obtained from these tests can be used to optimize individual training and recovery programs.
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