The Relationship Between Maximal Oxygen Intake, Body Fat and Bone Marker Measurements in Different Sports Branches

Objectives: The purpose of our study is to evaluate the interaction between maximal oxygen intake, body composition and some bone marker measurements in Turkish elite players. Methods: A total of 51 Turkish players of Turkish Super League from following disciplines were included in the study: football (25 players), basketball (12 players) and volleyball (14 players). Maximal oxygen intake as a cardiorespiratory fitness measurement and some anthropometric measurements such as body weight, fat mass, fat free mass were measured. We analyzed the serum samples for total serum 25(OH)D and calcium levels. The data of individuals were categorized as indoor sports (volleyball and basketball) and outdoor sports (football); also according to the branches. Results: In this study, it was found that, fat mass (p=.019) and fat free mass (p=.000) were significantly higher for indoor sports athletes. On the contrary, VO2 max intake (p=.001) and serum vitamin 25(OH)D (p=.000) levels were significantly lower in indoor athletes. For all participants, only 51.0% subjects had sufficient serum vitamin 25(OH)D. It was found that vitamin D levels was inversely related with body weight (spearman r=-0.41, p=.003), fat free mass (spearman r:-0.51, p=.000) and basal metabolic rate (spearman r:-0.35, p=.012). We found no significant correlation between total calcium levels and any of the other parameters. Conclusion: In Turkish athletes, better cardiorespiratory fitness and lower percent of body fat were associated with higher serum 25(OH)D level. All these data were independent of serum total calcium level.


Introduction
The skeletal system is the most important part of overall health for the athletic population.Up to 18 years, the bone mass reaches to 90% of its maximal level; declines after menopause in women and is largely influenced by genetic factors (Baile, McKay, Mirwald, Crocker, Faulkner, 1999).Besides genetics, other modifiable factors affect bone health, such as exercise, nutrition, smoking, medications and calcium intake (Whiting, Vatanparast, Baxter-Jones, Faulkner, Mirwald, Bailey, 2004).Physical activity plays a key role in bone mineralization till adulthood.Adequate formation of bone mass may reduce fracture risk by 50% to 80% (Nordstrom, Karlsson, Nyquist, Olsson, Nordstrom, 2005).Other factors that may contribute maximum peak bone mass are the percentage of body fat, serum total calcium, serum 25-hydroxyvitamin D (25(OH)D) and parathyroid hormone (PTH) levels (Heller, Thomas, Hollis, Larson-Meyer, 2015).PTH functions to maintain optimum blood calcium level.PTH and serum calcium levels regulate the formation of 1,25(OH) 2 D from 25(OH)D.
The 25(OH)D is needed to enhance absorption of calcium and phosphorus from the intestine.
That is why, serum 25(OH)D level is an important factor for optimizing bone mass (Sohl, Jongh, Heymans, Schoor, Lips, 2015).It is shown that the levels of serum PTH is inversely associated with the serum level of 25(OH)D (Gutierrez, Farwell, Kermah, Taylor, 2011).
It is reported that nearly one billion people have vitamin D-deficiency or insufficiency (Holick et al. 2012).Also there are conflicting information about the optimal serum levels of 25(OH)D.Vitamin D deficiency is defined by total 25(OH)D levels of <20 ng/mL while vitamin D insufficiency may be defined as a level of 20 to 31 ng/mL and levels of ≥32 ng/mL demonstrates sufficient levels (Kennel, Drake, Hurley, 2010;Bogunovic, Kim, Beamer, Nguyen, Lane, 2010).From the point of view for athletes' health, recent studies showed that vitamin D has a significant role on skeletal health, immune system and optimal sports performance (Halliday, Peterson, Thomas, Kleppinger, Hollis, Larson-Meyer, 2011;Earthman, Beckman, Masodkar, Sibley, 2012).The deficiency of vitamin D may lead an increased risk for stress fractures, infections and muscle sensitivity (Lappe, Cullen, Haynatzki, Recker, Ahlf, Thompson, 2008).The prevalence of vitamin D insufficiency and deficiency in athletes is about 55% with a higher incidence in winter/spring seasons and players of indoor sports (Farrokhyar, 2015).In a recent National Collegiate Athletic Association (NCAA) study, the prevalence is %33.6, although the study was carried out in the summer months (Villacis, Yi, Jahn, Kephart, Charlton, 2014).A recent meta-analysis found that 56 % of athletes had vitamin D inadequacy (Farrokhyar et al., 2015).Also, a sizeable number of indoor sports athletes do not meet their nutritional needs for vitamin D in addition to their inadequate endogenous synthesis (Larson-Meyer, Willis, Kentz, 2010).Vitamin D deficiency may be multifactorial, such as reduced synthesis, absorption and genetic predisposition of impaired vitamin D metabolism (Holick, 2007).Decreased cutaneous synthesis of vitamin D is the main reason of deficiency in athletic population which is the most important factor for indoor athletes (Close et al., 2013).Although dietary intake of vitamin D makes up a small quantity of total vitamin D needs, sources of dietary vitamin D including fish, dairy (especially enriched sources) and eggs.The main source of vitamin D is provided by UVB light, and its formation may be affected by age, season, location, clothing style, high-impact creams applied to the skin and skin pigmentation (Angeline, Gee, Shindle, Warren, Rodeo, 2013).
Another issue that has been discussed recently is the association between vitamin D and body composition.Excess body fat or being overweight is also increased risk for those who has low vitamin D levels in non-athletes (Drincic, Armas, Van Diest, Heaney, 2012).
Several investigators have reported the inadequacy or insufficiency of vitamin D for athletes but only limited study is reported the association of exercise, cardiorespiratory fitness and vitamin D. Studies have shown vitamin D deficiency and its relation with exercise types (Ceglia, Chiu, Harris, Araujo, 2011;Verreault, Semba, Volpato, Ferrucci, Fried, Guralnik, 2002).Maximal oxygen consumption is one of the measuring type of anaerobic capacity levels; Friedlander et al. (Friedlander, Genant, Sadowsky, Byl, Gluer, 1995)

Methods
Males aged 17 to 37 were recruited as volunteer participants.Athletes were selected from the summer camp which is located in Bolu, Turkey.A voluntary consent form was obtained from all the participants.Volunteers were healthy athletes who had white skin and were regularly practicing during the summer camping season.Subjects who took calcium or vitamin D supplements, have diabetes mellitus, cardiovascular diseases, neurological disorders, and other serious medical conditions were not included.Medical histories and other health parameters were questioned to determine the acute conditions that would affect cardiorespiratory fitness.The individuals thought to be unhealthy for study were removed.
This study was conducted from June 2016 to August 2016 to reduce seasonal variations.
Participants' blood samples were drawn into standard tubes with no additives, kept to clot for 30-60 min at room temperature, and centrifuged at 3500 rpm for 15 min.Pipetted serum samples were stored at -20 o C until analysis.The 25(OH)D concentration were measured via Diasorin 25(OH)D RIA and PTH by intact PTH IRMA.Vitamin D deficiency is defined as a total 25(OH)D levels of <20 ng/mL.Vitamin D insufficiency is defined as a level of 20 to 31 ng/mL, and levels of ≥32 ng/mL demonstrates sufficient levels (Bischoff-Ferrari H.A., Giovannucci E., Willet W.C., Dietrich T., Dawson-Hughes B., 2006).The intreassay coefficient for both analysis is less than 10%.The samples were analyzed at Gerede State Hospital Biochemistry Laboratory (Bolu, Turkey) for serum 25(OH)D.Blood samples were also determined for serum calcium levels by using a Technicon Autoanalyzer II.

Statistical Analysis
Statistical analyses were performed using the IBM SPSS Statistics Version 23.0 (SPSS Inc., Chicago, IL).Descriptive data are presented as an arithmetic means ±SD (SD).
Spearman correlation coefficients were used to determine the association of VO 2 max and body fat percent with bone markers.A p value of less than 0.05 was considered statistically significant.

Results
This study was conducted with a total of 51 male athletes including 14 volleyball, 12 basketball and 25 football players.Mean (SD) baseline measurements are shown in Table 1.
The mean age was 26.3±5.21years.The mean VO 2 max level of the athletes was 40.8±8.72 mL/kg/min; mean vitamin D level was 36.6±22.77ng/mL and mean total calcium level was 8.9±1.38 ng/dL.When branches categorized as indoor (volleyball and basketball) and outdoor (football) sports; we found that individuals in indoor sports were significantly higher fat mass (p= 0.019) and fat free mass (p=0.000).On the contrary, VO 2 max (p=0.001) and serum 25(OH) D (p=0.000) levels were significantly lower in the indoor group.Serum total calcium levels were not different between branches.Categorized version of some variables of participants are given in the Table 2.
Thirteen subjects (25.5%) were categorized as having deficient, with a serum vitamin 25(OH)D level of less than <20 mg/dL.For all population, only twenty six subjects (51.0%) were categorized as sufficient.When evaluated according to indoor and outdoor sports, there is found statistically difference; while twelve indoor sports athlete had serum vitamin When athletes evaluated in terms of max VO 2 levels, for all population, only 3 subjects (5.9%) had superior level.For athletes, there was significant difference for indoor and outdoor sports; while 11 subjects (44.0%) had was at levels of excellent (for outdoor sports), 3 subjects (11.5%) had levels of excellent (for indoor sports) (p<0.05).For total population very poor levels were found 26.9% of indoor sports; 12.0% for outdoor sports athletes (p<0.05)(Table 2).
When we evaluated the subjects according to the BMI classification, there was no subject that has under 18.5 besides over 30.Forty-one subjects (80.4%) had BMI between 18.5 to 24.9; besides ten subjects (19.6%) had BMI between 25.0 to 29.9; there was no statistically significant difference between groups (p>0.05).Table 3 presents the differences of age, body composition, Max VO 2 levels, and some bone marker measurements in terms of branches.VO 2 max (p=0.004) and vitamin D levels (p=0.000) of football players were significantly higher while BMR (p=0.000) and fat free mass (p=0.000) were statistically lower from volleyball and basketball players.Total calcium levels did not differ between groups.Football players had significantly higher VO 2 max (p=0.009) and vitamin D (p=0.000) levels than volleyball players.Similarly, their VO 2 max (p=0.004) and vitamin D (p=0.003) levels were statistically higher than basketball players.
There were no significantly difference between basketball and volleyball players for all parameters.When the data evaluated according to branches, BMR (p=0.000),fat free mass (p=0.000),VO 2 max (p=0.004) and serum 25(OH) D (p=0.000) levels were significantly different between groups.BMR and fat free mass of football players were lower while VO 2 max and serum 25(OH) D levels were higher than volleyball and basketball players (p<0.005).Only fat mass of football players were significantly lower than basketball players.
independent of serum total calcium levels.This study presents that, fat mass and fat free mass were significantly higher for indoor sports athletes.On the contrary, VO 2 max intake and serum vitamin 25(OH) D levels were significantly lower for indoor athletes.We know that serum vitamin D levels are affected at a moderate level in the diet.The sufficiency or insufficiency of vitamin D may be associated with genetic background of our Turkish athletes.
Further studies are needed for understanding the exact effects and metabolism of 25(OH)D, body composition and max VO 2 levels.Daily vitamin D and calcium intake may influence the participants' general health issues.From this point, determining dietary intake of vitamin D influences health outcomes in athletes from different branches would also be a valuable perspective for further studies.
also found a positive relation between bone mineral density, serum PTH and VO 2 max levels in women(aged 20-35 years).Although many researches have been studied on the relationship of exercise and bone density, there is no exact information about the association with cardiorespiratory fitness (VO 2 max).In summary, low serum vitamin 25(OH)D levels may be affective on the body composition.In other aspect, we know that, as mentioned above, serum vitamin 25(OH)D is related to serum calcium and PTH levels in terms of bone and skeletal health.Although the mechanism of serum vitamin D interactions with cardiorespiratory fitness is unclear, the association between exercise and bone mineral density and/or mass is well known.There is direct relationship between serum vitamin 25(OH)D levels and athletic performance, as well as sedentary/active individuals.Athletes need rapid growth of bone and muscle mass and relation to these needs, they have a high demand of vitamin D. Many factors that can cause lack of vitamin D in athletes.Beyond these, serum vitamin 25(OH)D level is important for maintaining bone health and homeostasis.We aim to show the differences between the branches (by separating indoor/outdoor) and for all participants for these parameters.It is known that vitamin D has an effect on athlete health, body composition and many other factors.From this point, this study aims to show the relation between serum vitamin D and calcium levels with the max VO 2 (as an aerobic capacity marker) and body composition in indoor/outdoor athletes, competing in different fields.Original side of our work is that, there was no enough study that shows the relation with vitamin D and aerobic capacity markers according to the neither branches nor indoor/outdoor sports.
25(OH)D deficiency; only one subject from outdoor sports had serum vitamin 25(OH)D deficiency (p<0.05).Twenty subjects (80.0%) of outdoor sports had sufficient serum vitamin 25(OH)D, on the other hand 6 subject (23.1%) of indoor sports had sufficient serum vitamin 25(OH)D levels.

Table 3 : Comparison of parameters between branches
* p<0.005,Kruskal wallis test was performed.Mann Whitney U test was performed to compare groups.Abbreviations: BMI, Body mass index, BMR, Basal metabolic rate

Table 4
presents the Spearman correlation coefficients between participants' cardiorespiratory fitness, some anthropometric measurements and vitamin D levels.Vitamin D level was inversely associated with body weight (p=0.003),fat free mass (p=0.000) and BMR (p=0.000).VO 2 max data was inversely associated with fat free mass (p=0.009),BMR (p=0.012) and body weight (p=0.012).There was no significant correlation of total calcium levels with any of the other parameters.