The Journal of the International Society of Sports Nutrition recently released a study that examined the relationships among biomarkers of iron status, athletic performance, growth and development, and dietary intakes in pre-adolescent and adolescent male and female athletes.
Biomarkers used to measure iron status in athletes include ferritin, soluble transferrin receptor (sTfR), and hemoglobin (Hb) concentrations. Previous studies have shown positive links between athletic performance measurements and ferritin and Hb concentrations, while sTfR concentrations have been inversely related to exercise. Therefore, exercise and athletic performance is impacted by iron status, which suggests that regular and adequate iron intake may be important for athletes.
Because iron is involved at the molecular level in oxygen utilization, it plays a critical role in sport. Oxygen is transported to the tissues by hemoglobin, a protein found in red blood cells which depends on iron. The most important determinant of athletic performance in an endurance athlete is aerobic endurance -- how much oxygen an athlete uses in a set period of time.
Between growth rates of bone and muscle and onset of menarche in females, coupled with athletic participation, young athletes, especially young females athletes, likely require more iron. “Our findings may also tentatively suggest that the sTfR biomarker may be more sensitive than the other iron biomarkers in adolescent female athletes experiencing rapid growth, compared to adult athletic females.”
Researchers studied 249 athletes, 179 males and 70 females. The subjects, who ranged in age 5-18 years old, provided blood samples, measurements, athletic performance, and dietary intake assessments.
Variables mentioned in the study included maturity offset from peak height velocity (PHV), percent body fat, estimated muscle cross-sectional areas, vertical jump height (VJ), broad jump distance (BJ), pro-agility time (PA), L-cone time, 20-yard dash time (20YD), power push up (PPU) force, dietary intakes, and ferritin, soluble transferrin receptor (sTfR), and hemoglobin (Hb) concentrations.
The primary findings indicated that athletic performance consistently correlated with Hb concentrations in males and with sTfR and iron intake in females.
There were no relationships between dietary intakes and ferritin, sTfR, or Hb. After partialling out age and height, VJ, PA, LC, and 20YD remained correlated with Hb in males. After partialling out iron intake, PA and LC remained correlated with sTfR in females.
In contrast to dietary iron intake, researchers found that dietary protein intake was related to growth and development in males, but did not impact females. The authors say future studies may be needed to examine the relationships among growth and development measurements and dietary protein intakes in males and females matched for biological maturity, rather than chronological age.
Nutritionist Susan Kleiner, PhD, told NutraIndredients-USA that this study is important as a contribution to the body of data of influencers on performance in adolescent athletes. “The differences in biomarker correlations between the genders despite similar age groupings may suggest that it is maturity rather than chronological age that has the greatest influence on the impacts and should be considered in the pediatric clinical setting.”
Indeed, the authors emphasize the importance of maturity, rather than age, when monitoring diet and athletic performance in young athletes: “We believe that the moderate correlations between sTfR concentrations and athletic performance, as well as the moderate correlations between athletic performance and dietary intakes, in the adolescent female athletes in the present study should not be ignored. Not only are children and adolescents a protected human subject population making it difficult to collect these data, but also adolescent female athletes may be considered an under-studied population.”
Kleiner, who advises female athletes, agrees with the authors who recommend “increasing dietary protein and iron intakes in young female athletes...”.
Iron status biomarkers demonstrated sex-specific relationships with anaerobic exercise performance in youth athletes, which may be more dependent on maturity status and dietary intake than age.
Kleiner further breaks down the findings: “What we have seen in this study is that elevated soluble transferrin receptor (sTfR) values are related to decrements in performance in female adolescents. Also that with elevated sTfR it is possible that if dietary iron intake is improved, lower body power and speed may improve in the female adolescent athlete. This is all significant because hemoglobin (Hb) is the most commonly measured blood value to screen for low iron, but Hb was not significantly associated with decreased performance in this study with female adolescent athletes.”
On the other hand, “Hb was associated with decreased athletic performance in pre-adolescent male athletes even when controlling for other related influences of growth and development, and dietary intakes,” added Kleiner.
The authors conclude that believe “these moderate correlations emphasize the need to collect additional data in adolescent female athletes in future studies to improve nutritional recommendations for this at-risk population.”
Source: Journal of the International Society of Sports Nutrition
Vol. 16, Article number: 42 (2019) doi: https://doi.org/10.1186/s12970-019-0306-7
“Sex-specific relationships among iron status biomarkers, athletic performance, maturity, and dietary intakes in pre-adolescent and adolescent athletes”
Authors: M.E. Shoemaker, et al.