The Association Between Iron and Vitamin D Status in Female Elite Athletes
Written by Ben Bunting: BA(Hons), PGCert. Sport & Exercise Nutrition. British Army Physical Training Instructor.
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For the past several years, research on the effects of vitamin D and iron on athlete performance has been conducted.
Despite the results of these studies, the relationship between the two is still unclear.
In a recent study, researchers from the University of California at Los Angeles (UCLA) investigated the association between vitamin D and iron status and the performance of female elite athletes.
The results indicate that athletes with higher levels of vitamin D and iron show increased performance in both physical and mental tests.
The findings of this study are relevant to athletes of all sports who are interested in developing a more healthy lifestyle.
Iron and Vitamin D
Iron and vitamin D are important nutrients that are not only essential for health but also impact physical fitness.
It is therefore crucial to assess the interactions between them. This review presents evidence from studies investigating the relationship between the two.
A number of studies have investigated the link between vitamin D and iron. However, these studies have mostly been focused on hematological indices such as ferritin and blood morphology.
A few have examined dietary intake and pre-season vitamin D levels. The association between the two nutrient is less pronounced on non-hematological parameters.
The results indicated a positive correlation between iron status and 25 (OH) vitamin D. This was confirmed by hematological indices of iron status. In addition, a reverse relationship between age and iron status was identified in females.
In contrast, this relationship was not observed in males. Nevertheless, there is a general increase in age-related risk of vitamin D insufficiency in female athletes.
Athletes who train indoors may have low levels of vitamin D. Furthermore, the effect of training environment on vitamin D status is not known.
Similarly, the relationship between vitamin D and muscle function is not well established.
A study used data on a subset of over 200 female professional athletes. Among them, there were seven sports disciplines.
Most were national teams. The majority of these athletes were Caucasian. The subjects were evaluated during the period of vitamin D synthesis. In addition, only venous blood samples were taken from each subject.
The data collection method was conducted by two researchers. Although the interviews were not supplemented, the participants were asked about their vitamin D and iron intake, as well as time spent outdoors.
Unfortunately, the data were insufficient to provide a more complete explanation of the anti-inflammatory properties of vitamin D.
Hence, it is recommended that athletes who train in cold climates supplement their diet with vitamin D.
Considerations for female athletes
Many studies have shown that female athletes are at risk of having a low vitamin D status. This study examined the relationship between iron and vitamin D in professional athletes.
It also showed the seasonal variance in the levels of these nutrients. The authors suggest that low concentrations of these nutrients in athletes may predispose them to bone pathologies.
Moreover, exercise-induced stress may lead to an inadequate supply of vitamin D.
The 231 female professional athletes who participated in the study represented seven sports disciplines.
The athlete selection was made by taking into consideration age, gender, total iron binding capacity and serum folate, vitamin B12 and magnesium levels. The research team measured the serum ferritin, serum copper, vitamin D3 and iron levels in the venous blood of these athletes.
In addition, they examined anthropometrics using an automated biochemical analyzer.
A significant difference was found between the two groups when it came to mean values of 25 (OH) vitamin D, total iron saturation, ferritin, and TIBC.
However, no significant difference was seen between the two groups when it came to serum magnesium, CRP, or ESR.
The study found that the average level of vitamin D in deficient players was 16.1 +- 2.1 ng/mL, while the average value for players in the healthy group was 25.6 +- 10.2 ng/mL.
Males and females in both groups had lower levels of serum 25 (OH) vitamin D. Females in both groups had lower levels of serum calcium and phosphorus.
The difference in the indices of reticulocytes was more evident, with an increasing tendency for males to have a higher TIBC and a decreased mean corpuscular volume, while the females had a lower CHr and RBC.
The study also showed the presence of a significant negative correlation between age and the indices of ferritin, TIBC, and MCVr.
This correlation is more apparent in females than in males, but the lack of data on hepcidin, interleukins, or nutrient intake prevented a more accurate explanation of the anti-inflammatory effects of vitamin D.
This study confirmed the association between vitamin D and iron status in female athletes. The findings also showed the importance of monitoring the interactions between these two nutrients.
Risks for Female Athletes
As it has been identified, female athletes are at high risk of nutrient deficiencies. There are a number of studies that have investigated the association between the two in physically active subjects.
In this study, the researchers examined whether the two nutrients interact in professional female athletes.
Deficiencies
The results revealed that most of the athletes had low serum concentrations of vitamin D3 and ferritin, but only a few had anemia. In the case of anemia, iron deficiency was more common than vitamin D deficiency.
The mean values of 25(OH)D were similar between the groups of athletes with normal and iron deficiency.
However, there was no significant difference in hemogram parameters between the groups. A Mann-Whitney U test was conducted to compare the mean values of the parameters in the two groups.
The lower mean values of the hematological indices in the group with reduced vitamin D concentration were associated with the reduction of ferritin and RBC, and the higher mean values of MCVr and TIBC in the group with a sufficient vitamin D level.
The correlation between the 25(OH)D and hematological indices was positive and confirmed by the results of non-heme indices. But the relationship between the two nutrients is not conclusive, since some of the studied parameters did not measure the non-heme indices.
This may be due to the fact that team were studying healthy subjects, which is a liitation of the research. A more accurate explanation of the anti-inflammatory effect of vitamin D is based on data on nutrient intake and time spent outdoors.
The present study included a large number of athletes, and it demonstrated that iron deficiency is a major contributor to the association between iron and vitamin D. Furthermore, it found that the rates of anemia in the studied athletes were significantly lower than those in previous studies.
The results of the recent studies demonstrate that the association between iron and vitamin D status in female elite athletes is not significant. A further study was conducted on 166 athletes.
Most of them were members of national teams. These subjects had undergone periodic medical examinations. They were excluded if they had a chronic disease, or had been admitted to the polyclinic due to sports injury.
The study used a cross-sectional design. Hence, it was difficult to determine the causal relationship between the nutrients.
Furthermore, the study was a pilot study and included only healthy young female athletes. However, its strengths and limitations were outlined below.
The study used a colorimetric ferrozine-based assay to measure serum iron and ferritin levels.
In addition, biochemical parameters such as serum magnesium, MCVr, TIBC, CHr, ESR and a variety of hematological indices were evaluated. The results showed that the mean values of the hematological indices in the reticulocytes were lower in the group with reduced vitamin D concentration.
The relationship between age and the iron and vitamin D status was moderately negative in females.
Conversely, in males, the relationship was slightly positive. A higher percentage of ID subjects was observed in the group with reduced vitamin D concentration than in the group with adequate vitamin D.
This may be due to post-exercise changes in plasma volume. The opposite relationship between the vitamin D and RBC was also observed. Several factors could account for this difference.
This study was done in a country where seasonal variation in vitamin D status is commonly observed. Athletes' training indoors, especially during winter months, can affect their vitamin D level.
It is therefore important to ensure optimal calcium levels in order to prevent bone pathologies. This can be done by implementing a prophylactic nutritional program. Besides, this can increase the quality of the bone.
The study had a positive correlation between the serum vitamin D and the non-heme indices of iron status. This is confirmed by the findings of the non-heme indices of ferritin.
Conclusions
In recent studies, the relationship between vitamin D and iron status in female athletes was investigated.
While it has been known that the prevalence of iron deficiency in female athletes is higher than in sedentary women, it is unclear how this relationship may be mediated.
Some authors suggest that endurance female athletes have increased iron requirements by 70 %. However, there is limited evidence to suggest this affects body stores. A few current studies have confirmed the relationship between the two nutrients.
In a study by Hamzullah Khan et al, serum ferritin was significantly associated with vitamin D. In another study by Moran-Lev H, hepcidin and vitamin D were studied in children with acute infectious diseases.
The results suggested that chronic inflammation requires additional nutritional support with iron.
It is important to understand the association between iron and vitamin D status in female athletes.
This is important because women are often considered at a high risk for developing iron deficiency. It has been shown that a moderately low iron status can negatively affect the performance of an athlete.
There are several factors that contribute to the development of iron deficiency. These include lack of dietary iron, inadequate absorbability of iron, and depletion of stored iron.
It is important to increase dietary intake of both haem-iron and total dietary iron in female athletes. In addition, dietary iron treatment methods such as dietary advice counselling, iron-rich foods, and novel iron-rich products should be used to improve iron bioavailability.
