Iron status is associated with endurance performance and training in female rowers

Journal Title (Medline/Pubmed accepted abbreviation): Med. Sci. Sports Exerc.
Year: 2012
Volume: 44
Issue: 8
Page numbers: 1552-1559
doi: 10.1249/MSS.0b013e3182517ceb
Summary of background and research design:
Background: Anemia caused by iron deficiency is one of the most common nutrient deficiencies afflicting about 16% of young women.  It is estimated that 30% of active young women, although not anemic, have iron deficiency that could negatively be affecting sports performance.

Hypothesis: Iron deficiency without anemia will be associated with lower oxygen capacity (VO2max), lower gross energy efficiency (energy produced divided by calories consumed), lower performance during a 4 km time trial, and a shorter reported training schedule in competitive rowers.

Subjects:  University-aged female rowers without anemia (48 total)

Experimental design: cross-sectional (no intervention)

Groups:  The women were divided into two groups: iron deficiency without anemia (n = 24) and iron sufficient (n = 24)

Protocol: A total of 165 female rowers were screened for iron status.  Blood samples were assessed for hemoglobin, hematocrit, red blood cell count, serum ferritin concentrations, soluble transferrin receptor, and α1-acid glycoprotein from which iron status was calculated.  Rowers with anemia were not eligible.  Rowers that were iron-depleted without anemia and those with healthy iron status were invited to participate.  Participants completed questionnaires regarding their diet, activity, and menstrual status.  They then reported to the testing site on two occasions after at least 2 hours of fasting and at least 4 hours after strenuous physical activity.  At the first session, anthropometrics (height, weight) and body composition (percent fat) were assessed, and then the participants were familiarized with the stationary rowing machine.  Maximum oxygen capacity (VO2peak) and maximum work rate (WRmax) were established.  Within the subsequent 3 days, the participant returned for assessment of endurance capacity.  With work load maintained at 85% of their previously determined VO2max, 4 km was completed as quickly as possible.  Respiratory gases and blood samples were collected throughout the test for assessment of energy expenditure and blood lactate concentrations, respectively.
Summary of research findings: 
  • Of all the rowers screened, 16 (10%) were anemic.
  • The rowers that were iron deficient without anemia did not have a lower iron intake or energy intake compared with the rowers with sufficient iron stores.
  • Rowers with iron deficiency without anemia reported 2 km personal records that were, on average, 18 sec slower than those with healthy iron status.
  • Despite differences in serum ferritin concentration (< 20 µg/mL is depleted) and total body iron; soluble transferrin receptor, hemoglobin, and hematocrit, were similar between groups.
  • Maximum heart rate, work rate, and average gross energy efficiency were similar between groups.
  • Iron deficiency was associated with a lower VO2max.
  • Performance on the time trial was significantly different between groups (17.43 ± 0.67 min for the healthy iron status group and 17.92 ± 0.87 min for the iron deficient group, P = 0.03), even after adjusting for potential confounders. 
  • A deficient iron status was associated with greater blood lactate concentrations during the time trial (p = 0.02).
  • According to self-reported training schedules, rowers with iron deficiency trained an average of 11 min/day less than with rowers with healthy iron status (p = 0.02).  No differences were revealed in regard to sleep or nap time, training speed, stress, concentration, motivation, discomfort, soreness, or fatigue.
  • Those that reported greater levels of training were not negatively affect by poor iron status in regard to their time during the time trial.  On the other hand, there was a stronger correlation between higher iron status and faster time trial times in those that trained more lightly.  This suggests that the negative effects of poor iron status can be overcome to some degree by training.

Key practice applications: Iron deficiency without anemia was associated with overall poorer performance in female rowers.  A very large proportion of female athletes have iron deficiency with and without anemia, and women need to assure that they are consuming adequate amounts of iron.  Some individuals absorb iron more efficiently, and iron supplementation may be recommended for some female athletes.

Key search terms for this article (5-7 terms): iron, anemia, female, rowing, ferritin
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