Micronutrient requirements of physically active women: what can we learn from iron?1-3
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Micronutrient requirements of physically active women: what can we
learn from iron?1–3
Sharon R Akabas and Karen R Dolins
ABSTRACT balance (10-12). A large gap on micronutrient requirements ex-
The health benefits of physical activity are well established and there ists in the literature regarding the impact of a weight loss regi-
is increasing recognition of the importance of fitness as a key mod- men’s that include exercise.
ulator of chronic disease. The impact of physical activity on micro- Much of the uncertainty regarding micronutrient requirements
nutrient requirements is a topic of tremendous interest to the lay and exercise stems from the lack of standardization or assessment
public, but the interest is in sharp contrast to data from well-designed of the nutritional status of the participants at entry, failure to
studies. Research in this area is poorly controlled for nutritional assess subject’s dietary intake, lack of standardization of the
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status of the participants, standardized exercise protocols, markers exercise protocol or program, lack of standardization of markers
and cutoff points for measurement of micronutrient status, and vari- and cutoff points, difficulty comparing one subject population
ability in subject characteristics. The micronutrient status of women (sex, menstrual status, age) to another, and failure to differentiate
in the general population is of concern, but it is not clear that physical between nutritional requirements during the initial training pe-
activity increases the requirement of most micronutrients. When riod and those of the period that follows the adaptive phase.
dietary intake is adequate, the results of most studies are either In the absence of clear recommendations, micronutrient sup-
equivocal or show no benefit to performance of supplementation. In plementation is often indiscriminate without regard to nutrient
the few instances where exercise does appear to increase an individ- status, due to the belief that it cannot hurt and may help. This
ual’s requirement, the increase can be obtained within the additional assumption is erroneous. In some instances, additional micronu-
calories required for energy balance. In the absence of consistent trient ingestion beyond the DRI not only has no effect on exercise
data, micronutrient supplementation is often indiscriminate without performance (12-14) but may have negative impact on general
regard to nutrient status. Because iron is such a key nutrient for health (15, 16).
physical activity, and the status in women is often compromised, it Many of these issues have been comprehensively addressed in
serves as a useful example of how current research limits the ability recent reviews of the topic of exercise and micronutrients (13, 14,
to make recommendations regarding the impact of exercise on mi- 17). This article uses iron as an example of how the limitations in
cronutrients requirements in women. With the recent recognition of current research constrain the ability to make clear recommen-
the importance of physical activity to the prevention and treatment of dations regarding the impact of exercise on micronutrients re-
chronic diseases through the life span, more attention should be quirements in women. The article concludes with the practical
focused on the impact of exercise on micronutrient requirements, implications of the ambiguity, and suggestions for future re-
especially in the context of weight loss regimens. Am J Clin search.
Nutr 2005;81(suppl):1246S–51S.
KEY WORDS Exercise, physical activity, iron, micronutri- BRIEF OVERVIEW OF IRON PHYSIOLOGY AND
ents, women, supplementation, nutritional status, dietary intake, ex- REQUIREMENTS
ercise protocol, markers Iron is a critical nutrient for active individuals, male and fe-
male alike. It plays a key role in energy production as a carrier of
oxygen, both in the form of hemoglobin in the blood and myo-
INTRODUCTION globin in the muscles. Additionally, iron is a part of the cyto-
chromes found in the electron transport system.
Though the health benefits of physical activity are indisput-
The recommended dietary allowance (RDA) for premeno-
able (1– 8), its impact on micronutrient requirements is much less
pausal women is 18 mg daily. While additional iron is recom-
well established. In the case of many micronutrients, women
mended for pregnancy and lactation, an increased intake is not
have inadequate intake (9), and a deficiency has a known detri-
mental impact on physical performance. Less clear is whether 1
From the Institute of Human Nutrition (SRA) Teacher’s College (KRD),
physical training and physical activity increase the requirement
Columbia University, New York.
of particular micronutrients, and whether amounts in excess of 2
Presented at the conference “Women and Micronutrients: Addressing the
the dietary reference intakes (DRIs) should be recommended for Gap Throughout the Life Cycle,” held in New York, NY, June 5, 2004.
physically active individuals. In the few instances where exercise 3
Address reprint requests and correspondence to SR Akabas, Institute of
does appear to increase an individual’s requirement, the increase Human Nutrition, Columbia University, 630 West 168 Street, PH 1512-East,
can be obtained within the additional calories required for energy New York, NY 10032. E-mail: sa109@columbia.edu.
1246S Am J Clin Nutr 2005;81(suppl):1246S–51S. Printed in USA. © 2005 American Society for Clinical NutritionMICRONUTRIENT REQUIREMENTS OF PHYSICALLY ACTIVE WOMEN 1247S
recommended for physically active women. A tolerable upper hemolysis, and impaired absorption. Endurance athletes are
level (UL) has been set at 45 mg daily for all adults to avoid the known to experience sports anemia, a dilution of ferritin and
gastrointestinal distress often experienced with doses above this hemoglobin due to the plasma volume expansion that occurs with
amount (18). training. This is a transient effect that occurs when plasma vol-
Menstruating women carry an increased risk for iron defi- ume increases more rapidly than the increase in red blood cell
ciency regardless of training status due to monthly blood loss. mass, and typically results in a dilution of ferritin and hemoglo-
Adding to this concern, survey data shows that female athletes bin of 15% (25).
often underconsume calories (19 –21), making it less likely that Long distance runners may experience greater gastrointestinal
they will consume adequate dietary iron. losses through the feces. Though female data have not been
As iron clearly plays a critical role in athletic performance and provided, Telford and colleagues (26) studied hemolysis in male
deficiencies are not uncommon, female athletes are often advised triathletes after a 1-hr cycle and run. They found that plasma free
to supplement iron without prior determination of hematological hemoglobin and serum haptoglobin concentrations were in-
parameters. This practice is discouraged by medical practitioners creased after both exercise bouts, but the increase was 4 times
due to the danger of toxicity from iron overload. greater after the run than after the cycle. The authors con-
Iron depletion occurs in 3 stages. The first stage, depletion of cluded that footstrike is the major contributor to hemolysis
stores, is identified by serum ferritin below 12 g/L. The second during running.
stage, iron-deficient erythropoiesis, is identified by increased Iron losses may occur through sweat and desquamated epithe-
concentrations of transferrin and reduced transferrin saturation. lial cells. One early study conducted in healthy males, in which
Stage 3, anemia, is characterized by microcytic hypochromic red the skin was carefully cleaned to remove desquamated epithelial
blood cells and diagnosed as hemoglobin below 12 mg/dL in cells and thus isolate sweat, found sweat iron losses to be small
(22 g per liter sweat) and thus unlikely to have an impact on iron
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females and below 13 mg/dL in males.
While it is clear that iron deficiency anemia impairs athletic requirements (27). A more recent study of female athletes found
performance, it is less clear whether iron deficiency without that sweat losses of iron declined with time (28). The greatest
outright anemia will have this effect. Thus a focus of current concentration of iron in sweat occurred during the first 30 min of
research is whether iron deficiency without anemia will impair exercise, and was lower in a hot environment than a neutral
performance and, if so, whether and at what point iron supple- environment. Sweat iron concentration in this study was related
mentation should be initiated. to ferritin concentration, suggesting that conservation of iron
The choice of markers of iron deficiency has complicated may occur with reduced stores. The authors estimated that 5.7%
clarification of this issue. Serum ferritin, the most commonly of daily absorbed iron, or 1.2 mg/dL, would be lost by exercising
used marker, may become elevated in response to inflammation, females during the first hour of exercise, and that this could
infection, liver disorders, malignancies, and exercise-induced contribute to depletion of iron stores.
hemolysis (22). Iron deficiency may therefore be masked in The effect of exercise on iron absorption has been questioned.
certain individuals. Also clouding this issue is the lack of stan- While female data are not provided in this area either, moderate
dardization in cutoffs used for diagnosis. Though serum ferritin intensity exercise did not impair iron absorption in a study on
concentrations below 12 g/L is typically considered to be the male cyclists exercising at 60% VO2max for one hour (29). To
marker for depletion of stores, researchers have use varying the contrary, absorption of 100 mg ferric sodium citrate led to a
levels in developing inclusion criteria for their studies. 48.2% increase in serum iron concentrations when taken 30 min
Measurement of serum levels of soluble transferrin receptor before exercise as compared with an increase of 8.3% when taken
(sTfR) has recently become the gold standard for identifying iron at rest.
deficiency in its earliest stage. First described in 1963, sTfR is Based on the available research, it is difficult to arrive at
bound to the cell membrane and mediates the endocytic transfer conclusions regarding the impact of exercise on iron require-
of iron from transferrin into erythroid cells. Levels increase when ments in women. If there is an increase in requirements, it will
iron stores are depleted or turnover stimulated. Small amounts most likely be for women engaged in long distance running due
appear in the blood and can be measured. This marker, therefore, to gastrointestinal losses and footstrike hemolysis. To fully clar-
reflects both iron stores and the rate of erythropoiesis, and has ify the confusion, future research protocols must control for diet,
been found to be more sensitive to iron deficiency than serum menstrual status, standardize exercise protocols, and use sTfR as
ferritin as well as more indicative of the functional pool of iron the primary marker of iron status.
(23). At this time, this marker is the most accurate indicator of
iron stores, and least confounded by factors such as inflammation
(24). Values may be confounded by muscle growth, as this will
EFFECT OF TRAINING ON IRON STATUS
result in a rise in sTfR levels due to a need for increased eryth-
ropoiesis. Thus muscle growth must be taken into account Strength training
during analysis of changes in sTfR. In addition, the most Numerous studies have looked at changes in iron status that
appropriate cutoff point must be clearly established to allow a occur with training. In a study designed to examine the effects of
meaningful consensus to emerge regarding physical activity resistance training on iron status, Murray-Kolb and colleagues
and iron requirements. tested 17 older, postmenopausal women (54 –71 y old) and 18
men (56 – 69 y) before and after a 12-wk resistance training
program (30). Diet including bioavailability of iron was evalu-
DOES EXERCISE INCREASE IRON REQUIREMENTS? ated with a 3-day food log, supplements accounted for, and com-
Proposed mechanisms for an increased requirement for iron pliance monitored. All hematological measures, including iron,
include increased losses in sweat, feces and urine, intravascular transferrin, ferritin, and sTfR were within normal limits for both1248S AKABAS AND DOLINS
genders at baseline and after training. However, women did iron status and dietary intake, variability in subject characteris-
experience a significant decrease in ferritin and a trend toward tics (trained versus untrained), exercise protocols, parameters
increased TIBC, whereas men experienced a rise in sTfR, prob- used for cutoffs, and use of different markers for measuring iron
ably related to an increase in lean mass, which was not achieved depletion.
by the women. Thus the researchers found that men and women A series of studies from the lab of Brownlie and colleagues
experienced sex-specific changes in iron status, and noted that a tested the hypothesis that iron supplementation would help de-
rise in sTfR during resistance training may indicate muscle ficient but non-anemic women progress through a training pro-
growth rather than iron deficiency. Deruisseau et al (31) designed gram by improving endurance capacity (34 –36). Subjects in
a similar study with collegiate men and women participating in a these studies were 18- to 33-y-old untrained but active women
12-wk weight training program. Diet and adherence were mon- who presented with normal hemoglobin (쏜120 mg/L) and low
itored. Contrary to the previous study, only the men experienced serum ferritin based on a cutoff of 16 g/L. Subjects were given
a decline in ferritin, and no change in sTfR was observed in 8 mg elemental iron BID (35, 36) or 10 mg BIO (34) versus
subjects of either sex. placebo for 6 wk. A 4-wk training protocol was carried out using
Despite the care taken by both research teams to control for
cycle ergometers. The studies were all carefully controlled for
diet, and to use state of art assessment of iron status, these 2
diet using 4-d food logs and compliance with the protocol was
studies fail to resolve the question of whether strength training
monitored.
increase iron requirements, perhaps due to differences in exercise
protocols. Clarification is needed regarding whether the ob- In the first of this series (34), subjects in the iron-supplemented
served rise in sTfR during resistance training indicates muscle group experienced an increase in serum ferritin, iron, and trans-
growth or iron deficiency. ferrin saturation, while sTfR concentration decreased. The pla-
cebo group was without significant changes in these parameters.
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Endurance capacity and exercise performance were tested
with a 15-km time trial at a level of resistance consistent with
Endurance training
70% VO2 max. While both groups improved their finish time in
The iron status of female triathletes was assessed before and a time trial after the training program, the supplemented group
after a competition consisting of a 1.5 km swim, 40 km cycle, and was found to improve twice as much as the placebo group. Fur-
10 km run (32). Of the 12 athletes studied, 2 presented with ther analysis demonstrated that the effect of supplementation on
anemia based on hemoglobin below 12 mg/dL and 4 met the endurance capacity was most pronounced in those who exhibited
researcher’s criteria for iron deficiency of ferritin below 10 g/L
higher sTfR levels at baseline, suggesting an increased efficiency
before the event. Serum transferrin receptor was elevated in one
of oxygen utilization at the tissue level.
subject before the race. After the race, ferritin concentration
A subsequent study was conducted by the same laboratory (35)
remained elevated after correction for hemoconcentration, while
to further elucidate the effect iron depletion without anemia
sTfR levels did not change. The dietary intake of iron in these
athletes was not assessed, leaving it unclear whether iron defi- would have on women’s ability to improve aerobic capacity
ciency and anemia occurred as a result of increased requirements during a 4-week training program. The exercise protocol was the
or inadequate intake. same as the previous study. Here, however, though serum fer-
Ashenden et al (33) conducted a retrospective review of he- ritin, iron, and transferrin saturation increased in the supplement
matological status from 6 y of data on female rowers, basketball group sTfR did not significantly change. Exercise testing
players, and netball players to establish changes that occur revealed greater improvements in both absolute and relative
through training seasons and how the mode of training might VO2 max in the supplement group as compared with placebo.
effect those changes. Mean serum ferritin concentrations for all Using sTfR to further delineate iron status, results were strat-
athletes experienced a decline in serum ferritin of about 25% ified between those with initially elevated levels indicating de-
during the training season. While the means did not drop below creased stores and erythropoiesis and those with normal levels
normal at any point, a sub-group presented with low concentra- using a cutoff of 8.0 mg/L. Those with higher baseline sTfR were
tions (7.5 앐 2.7 g/L). Rowers (non-weight-bearing) maintained found to respond the most to iron supplementation, exhibiting the
higher levels than basketball and netball players (weight- greatest improvements in VO2max. Exercise performance was
bearing) throughout the season. Again, dietary intake was not not tested in this study.
evaluated and sTfR was not measured. In the third study of this series (36), a time trial was again
Based on these few studies, one of which focused on an acute introduced as a performance measure. Physiologic responses
exercise bout, the other on long-term training, it is once again too were stratified by baseline sTfR concentrations using a cutoff of
difficult to arrive at a conclusion that could serve as the basis for 8.0 mg/L, revealing a significant effect of supplementation on
a recommendation for or against iron supplementation in re- % VO2max in the time trial in those subjects with baseline ele-
sponse to training. A major obstacle to arriving at a conclusion is vated sTfR. Improved performance in the time trial approached
the failure of each study to assess dietary intake and correlate significance in this group compared to placebo.
with hematological changes. The results of these studies demonstrate the value of including
sTfR as a marker for functional iron deficiency. As the authors
note, further research is needed to develop the most appropriate
EFFECT OF IRON SUPPLEMENTATION ON cutoff value so recommendations for supplementation can be
NONANEMIC, IRON-DEFICIENT WOMEN accurately made.
Earlier studies supplementing iron in non-anemic women Using another population, Friedmann and colleagues (37)
have been equivocal. Reasons for this include lack of control of studied the effect of iron supplementation in adolescent male andMICRONUTRIENT REQUIREMENTS OF PHYSICALLY ACTIVE WOMEN 1249S
female trained athletes with serum ferritin levels 쏝20 g/L and HIGH-RISK GROUPS
normal Hb levels. Athletes were given 100 mg elemental iron Certainly specific populations are at an increased risk for iron
twice a day or placebo for 12 wk. A treadmill performance test deficiency, including adolescents experiencing a growth spurt
was administered before and after the treatment period. Ferritin especially once they begin menstruating. Inadequate energy in-
concentration increased significantly in the supplement group, take has been identified from numerous surveys of female ath-
while blood volume, red blood cell volume, and total body he- letes (20 –21), which increases the likelihood of inadequate iron
moglobin did not change in either group. VO2max and O2 con- intake. Individuals adhering to a strict vegetarian diet are ham-
sumption increased significantly in the iron group, although it pered by the diminished bioavailability of non-heme iron. In
should be noted that the increase was slight, and relative VO2max addition, they are likely to consume food substances that impair
did not reach significance. sTfR was not measured, perhaps pre- absorption such as phytic acid, polyphenols, calcium and phos-
venting the researchers from demonstrating an increase in eryth- phate salts, and soy protein, placing them at further risk. Due to
ropoesis and masking a more significant improvement in a sub- these factors, the RDA for premenopausal vegetarian women is
group of their population. Furthermore, previous studies were 32 mg per day, almost twice the RDA for nonvegetarians (18).
successful at improving aerobic capacity and iron status with a In a recent review, Barr and Rideout noted that iron intake is
much smaller dose of supplemental iron, leaving open the ques- similar among vegetarian and nonvegetarian athletes (40). The
tion of just how much iron is necessary to obtain the desired failure to meet the increased RDA for vegetarians is probably
results. responsible for the higher incidence of functional anemia (nor-
Brutsaert and colleagues (38) used maximal voluntary con- mal Hb with low ferritin) reported in this population. Another
tractions (MVCs) to test progressive muscle fatigue in 18- to review also concluded that a vegetarian diet may be a risk factor
45-y-old women with normal hemoglobin (쏜110 g/L) and low in iron deficiency, particularly for female runners (41).
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ferritin (쏝20 g/L) given a supplement of 10 mg elemental iron Active women frequently remain physically active during
or placebo. Serum transferrin receptor, serum iron, and total iron pregnancy or may be unaware that they have become pregnant.
binding capacity were measured. After a 6-wk training period, Iron requirements increase significantly during pregnancy, and
sTfR concentrations were found to rise in the placebo group, maternal anemia has been associated with an increased risk of
indicating a decrease in available iron. Serum iron and transferrin preterm delivery (42). Therefore, it is imperative that women of
saturation rose in the treatment group, indicating an improve- childbearing ages, particular those with multiple pregnancies,
ment in iron status. The rate of decline in MVCs was less rapid in monitor iron status carefully.
the supplement group as compared with the placebo group, sug-
gesting improved iron status at the tissue level.
Non-iron deficient adolescent male and female swimmers RECOMMENDATIONS FOR IRON SUPPLEMENTATION
were studied for a 6-mo period while training for competition
(39). A strength of this study was the attention paid to menstrual The degree to which exercise itself increases iron requirements is
unclear. While long-distance runners may experience gastrointes-
cycle and consequent blood loss. All subjects presented with
tinal bleeding, it is likely that these losses will be compensated for by
normal levels of hemoglobin and ferritin (cutoff of normal was 7
an increase in iron absorption (25). Sweat losses of iron do not
ng/mL), but sTfR was not measured. One group was given an iron
appear to be of a degree to cause concern (27).
supplement of 47 mg, a second group was counseled on a high
It is clear that iron supplementation should never be initiated
iron diet plan providing 26 mg of iron and a third group was
without prior determination of iron status, as iron overload pre-
included as a control without either intervention. Compliance
sents serious health issues. A group of male French elite cyclists
with diet and supplementation was monitored. Dietary analysis
were found in 1 study to have hyperferritinemia as a result of
showed that all groups met the RDA for iron. No performance excessive enteral and parenteral iron supplementation (43),
benefit was found with supplementation in the absence of iron which may increase the risk of liver disease. Hemochromatosis is
depletion. a hereditary disorder that can result in iron overload. Supplemen-
Given the low cutoff used for serum ferritin, combined with tation might lead to toxic levels in athletes with this disorder.
the apparent adequate intake for all participants, it is not surpris- Those who supplement need to be aware that the body does not
ing that supplementation did not have an impact. In fact, this have a mechanism by which to excrete excess iron, and that
study was designed to deter unnecessary and indiscriminate sup- excess iron will act as a pro-oxidant, carrying with it a risk of liver
plementation that is common among female athletes. cancer and cardiovascular disease. Additionally, dietary iron
These studies suggest that iron supplementation in nonanemic, intake has been positively associated with the incidence of type
iron-deficient women improves endurance performance. Al- 2 diabetes in postmenopausal women (44).
though the range of supplemental iron was tremendous (8 mg/d Governing groups must set protocols for evaluating iron status
to 100 mg/BID), it appears that 8 mg/d may be sufficient to and initiating iron supplementation. A recent survey of NCAA
achieve improvements. Three of these more recent studies (34- Division I-A schools found that screening for iron deficiency was
36) demonstrate that by controlling for dietary iron intake, re- not routine, and that there is a wide degree of variability in the
ducing the variability in chosen markers, and by choosing a criteria used for diagnosis and treatment (45). Perhaps most in-
marker that is not confounded by inflammation, it is more teresting, hemoglobin and serum ferritin together were most
likely to reach a consensus regarding physical activity and often used to determine iron deficiency in the institutions re-
iron. The 1 study that showed no improvement is an affirma- sponding to the survey, demonstrating that iron deficiency with-
tion that supplementation is only warranted in the presence of out anemia is not routinely identified. Serum transferrin receptor
iron deficiency (39). concentration is currently considered the most reliable way to1250S AKABAS AND DOLINS
identify iron deficiency and should, in the opinion of some sci-
entists, become the standard for assessing the iron status of ath-
letes (16).
In an intriguing recent study of 321 early postmenopausal
women (46), dietary iron was positively associated with bone
mineral density in those women who had mean calcium intakes
ranging from 800 to 1200 mg calcium daily. The relation re-
mained after protein, which is also positively associated with
bone mineral density, was factored out. The authors suggest that
iron may play a role in the prevention of stress fractures in both
the elderly and elite female athletes. Given the incidence of
disordered eating in this population and its effect on bone mineral
density, this study provides more ammunition for convincing
female athletes to forego energy and nutrient deficient diets in the
quest for leanness. FIGURE 1. Approach to insuring nutritional adequacy. Factors along the
Protocols will be difficult to develop unless testing and treat- left side of the diagram determine micronutrient requirements. In the case of
ment become more standardized. Nielsen and Nachtigall (47) exercise, a behavior, there may be an increase in micronutrient requirement.
In instances where the requirement cannot be met by food, supplementation
recommend using a pharmaceutical iron preparation of 100 mg/d may be warranted. (Adapted from reference 48).
with a known high bioavailability for a period of 3 mo, with the
conditions for testing standardized and reported. They feel that
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supplementation should be recommended for those athletes with
serum ferritin 쏝35 g/L to reverse up-regulation of mineral • lack of standardization of the exercise protocol or program
absorption and prevent an increased absorption for other poten- • variability in subject population
tially toxic metals along with iron. The need for such high • lack of standardization of markers and cutoff points
dosages should be assessed in future studies, especially when • failure to differentiate the training period from the steady
in cases of mild deficiency, 8 –10 mg/d may be sufficient for state period that follows the adaptive phase
repletion. • assessment as to whether a change in micronutrient status is
In the studies reviewed above, diagnosis of iron deficiency has physiologic and adaptive, not pathologic (increase in sTfR
been made with a range of serum ferritin levels (7 g to 35 g). due to increased LBM versus diminished stores)
Some of the more recent studies measured sTfR, others did not. When trying to translate findings from the literature to partic-
Few controlled for diet or initial iron status. Some studies were ular athletes, it is important to assess the similarities and differ-
conducted on trained individuals, others on individuals initiating ences between the study population and the consumer. The needs
an exercise program, and exercise protocols varied in intensity, of women exercising to achieve fitness are likely to differ from
duration, and frequency. As a result, clear recommendations are those of competitive athletes concerned with exercise perfor-
difficult to make. mance. Elite athletes may train at much higher intensities and for
longer durations than the typical athlete, but they may also con-
sume many more calories.
PRACTICAL APPLICATIONS AND With the widespread public health recommendation that phys-
RECOMMENDATIONS FOR FUTURE RESEARCH ical activity be incorporated into weight loss regimens, the issue
Despite an upsurge in interest in physical activity, for most of micronutrient status in women on calorie-restricted diets who
vitamins and minerals, current research is not conclusive enough engage in regular physical activity deserves immediate attention.
to provide specific micronutrient recommendations to physically Until these issues are resolved, a primary goal for active women
active women. It is clear that they need to get at least the RDA for should be to obtain at least the RDA of all micronutrients. As with
micronutrients, and that many women fail to do so for several the general recommendation to women, regardless of physical
vitamins and minerals. Therefore, a primary practical implica- activity level, it should be emphasized that micronutrient con-
tion is to assess the micronutrient intake of any women engaged sumption above the DRIs will not improve performance and that
in a physical activity program, or about to embark on a program, excessive intakes of micronutrients should be avoided. If intake
and make sure that her intake at least meets the RDAs. is not adequate, the scheme recommended by Zeisel (48) (Figure
With regard to iron and many other micronutrients, several 1) can be used to determine the best route to establishing suffi-
articles in this supplement stress the importance of a woman ciency.
being replete at the outset of her pregnancy. Although young The authors have no personal or financial conflict of interest related to this
female athletes may be focused on performance, and the idea of project.
pregnancy may seem remote, the importance of educating them,
their physicians, and their parents about starting pregnancy “with
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