Fortify yourself – no sweat!

Sweating, iron losses and performance

As we mentioned above, iron status can be affected by sweating due to losses of iron in sweat. Sweat excretion from the sweat glands is primarily a mechanism of cooling down (ie reducing the body’s core temperature), but iron loss in sweat is also an associated and undesirable consequence^(18,19). Of relevance for athletes is that the loss of iron in sweat is generally higher in athletes undergoing intensive training (and who therefore sweat regularly) than in sedentary healthy individuals. Research indicates that the daily sweat-related iron loss is estimated to be 1–2mgs per two hours exercise, which is equivalent to between 1% and 3% of recommended daily intake of iron for women and men respectively^(20-22).

Although the amounts of iron lost via sweating are quite small, they are not insignificant, especially when you consider that the recommended daily intake of iron from the diet is 8mgs per day for men and 18mgs per day for women⁽²³⁾. Moreover, even when sweat loss of iron is not an issue, a number of studies have emphasized the importance of maintaining iron balance (ie making good any iron losses) for optimal work capacity and the physical fitness of athletes⁽²⁴⁾.

Given the need to maintain an optimum iron balance, especially when training in hot conditions, some researchers have proposed that routine, low-dose iron supplementation should be considered by all hard training athletes, especially women of menstruating age. For example, a randomised double-blind, placebo-controlled trial of iron supplementation found that low-dose iron supplementation attenuated fatigue and declining iron stores in female officers undergoing military training⁽²⁵⁾. In other studies, routine iron supplementation has also been recommended for all non-anemic endurance athletes on the basis that mild anemia can substantially decrease the capacity for performance of physical exercise^(26,27).

New research

If you’re an endurance athlete and train hard or regularly in the heat, will a low-dose iron supplement deliver real benefits – even though you are not iron deficient? It turns out that until recently there was no data with which to answer this question. But now an innovative study by a team of Japanese scientists has investigated the effect of giving iron supplements to healthy non-anemic athletes on their fatigue, mood states and sweating profiles during a training intervention⁽²⁸⁾. Published in the journal ‘Contemporary Clinical Trails Communications’, the athletes were supplemented either with a highly bioavailable iron formulation (SunActive® Fe) or placebo during a 4-week training intervention period.

The participants were recruited from a number of sports clubs in the Tokyo area. There were two groups of participants: 51 professional soccer and futsal players, and 44 healthy adult female athletes with extensive ‘hot yoga’ (an energetic style of yoga performed under hot and humid conditions) experience. In addition to the participants’ specialization, all had to fulfil the following criteria:

·       Engaged in regular endurance training.

·       No major illnesses or other medical conditions.

·       Over 20 years of age.

·       No prior history of iron deficiency (ie hemoglobin:13.5–14.5 g/dL (for males); 11.5–12.5 g/dL (for females).

·       No previous history of any fatigue-related pathology.

·       Not taking any medication or iron supplements.

·       No history of sleep disorder.

·       Reported to be regularly menstruating (female participants only).

·       Not consuming more than 100mgs of caffeine or 20 grams of alcohol per day.

Both the male and the female groups of participants were randomized to one of two groups (see figure 1):

·       Intervention - supplemented with low dose (3.6mgs per day) of a highly bioavailable iron formulation (SunActive® Fe) for 4 weeks while training continued.

·       Placebo – supplemented with an inert placebo for 4 weeks while training continued.

In a sense, this resulted in two separate studies (one on the male soccer/futsal players and one on the female athletes) being carried out in parallel. In both sets of athletes, training was conducted in hot conditions, which ensured sweating occurred. Importantly, both the athletes and researchers were blinded as to which athletes took iron and which took placebo (very important when assessing subjective qualities such as mood and fatigue (see below).

Figure 1: Schematic outline of experimental design

Before and after the 4-week intervention, the athletes were assessed for their levels of fatigue, stress profiles, as well as their quality of life (using the profile of mood state (POMS) test or a visual analogue scale questionnaire. In addition, saliva samples were taken to assess stress biomarkers. These markers included salivary α-amylase (a saliva enzyme that breaks down carbohydrate in the mount and which is known to increase during periods of physiological stress), salivary cortisol (cortisol is a stress hormone), and salivary immunoglobulin A (a ‘first defence’ component of the immune system that is known to decline during periods of stress).

What they found

The key findings were as follows:

·       All negative mood state scores in the POMS test decreased when the athletes supplemented with iron. This resulted in lower scores for anger/hostility, depression, confusion, fatigue/inertia and tension/stress. In plain English, iron supplementation improved the athletes’ mood and frame of mind.

·       The degree of sweating and perceived exertion during exercise was reduced in the iron-supplemented athletes compared to the placebo athletes.

·       A significant reduction in tired feelings or feeling of exhaustion following exercise was noticed in the iron supplemented athletes, whereas no change was observed in the placebo athletes.

Overall, the study authors concluded that their results ‘showed iron supplementation aided the psychological recovery of fatigue and reduced the burden of exercise, rendered relief from tired feelings and significantly improved  mood disturbance among the athletes’, and that ‘such a recovery from subjective fatigue could be attributed to the maintenance of iron metabolism and status in the body’.

Practical implications for athletes

The findings above add a new dimension to iron nutrition for athletes. Bearing in mind the study was double blinded, and used 95 participants (giving it fairly good statistical power), it seems that a low-dose, well-absorbed iron supplemented provided significant mood and well being benefits for the athletes taking iron – most likely by helping to offset iron losses in sweat. Some caution is required however since the exercise performed over the 4-week intervention was not standardized and no measures of exercise performance during exercise were carried. Moreover, the actual amounts of iron lost in sweat were not monitored.

Despite these caveats, the subjective benefits of iron supplementation were significant. And while there were no measures of physical performance carried out, the important of subjective feelings when assessing fatigue, recovery and performance should not be underestimated. When it comes to readiness to train, research indicates that perceived effort and fatigue can be just as effective as objective means of physiological measurement (see this article)⁽²⁹⁾.

Moreover, a research review compared subjective vs. objective recovery testing measures from a number of previous studies. Specifically, it compared mood state questionnaires vs. stress hormone and lactate monitoring – ie what athletes self-report in terms of how they feel compared with physical measures of recovery or lack of recovery. In a nutshell, subjective monitoring scored very highly indeed against the objective measures, finding that ‘subjective measures were more sensitive and consistent than objective measures in 22 of the 54 analyzed studies’, and that ‘objective measures were generally unresponsive to acute changes in training load⁽³⁰⁾’.

To conclude, iron insufficiency still seems to be a major challenge for athletes – of all ages, sports and abilities. However, this is particularly the case for younger athletes, especially women and those who follow vegetarian and vegan diets. When a rested and otherwise well athlete feels persistently fatigued or just ‘lacking in sparkle’ for no obvious reason, an iron insufficiency should at least be considered as a possible cause – particularly for younger female athletes or those following strict vegan diets. In this situation, the athlete should approach their physician and ask for a comprehensive iron status test – looking at not just HB but ferritin and STR levels also. In addition, athletes think about ways of increasing dietary iron intake and reducing any iron losses. The tip panel below provides further information.

TIPS FOR INCREASING DIETARY IRON INTAKE

• If you’re not a vegetarian, try to include some lean cuts of red meat in your diet once or twice each week.
• If you are, try and include more beans (especially lima beans), lentils, dark green leafy vegetables as well as eggs and nuts.
• Increase your intake of vitamin C-rich foods (citrus fruits, berries, new potatoes, broccoli, sprouts, tomatoes, peppers, kiwis etc.). Vitamin C helps convert iron from a less absorbable form (Fe3+) in the body to a more absorbable form (Fe2+) making it up to 4 times more bioavailable!
• Don’t drink tea and coffee with meals as the tannins present strongly bind any iron present making it less available to the body.
• Pure bran is very high in phytates, which bind iron. If you want more fibre, don’t use bran products; get it by eating whole grain breads and cereals in the first place.
• Cook using stainless steel cookware, which can add useful amounts of iron to cooked foods.
• If you are at a higher risk of an iron shortfall (see below), consider using a daily, low-dose iron supplement, taken away from other supplements or food.

IRON DEFICIENCY RISK

All of the factors below can contribute to an increased risk of an iron deficiency. Those marked with an asterisk indicate a more significant risk.

• My sport involves significant volumes of running or other forms of endurance exercise*
• I am female
• I have regular periods*
• I am under the age of 20
• I have had children
• There is a history of anaemia in my family
• I am a vegetarian
• I am a vegan*
• I drink tea and coffee with my meals*
• I use bran products (cereals with added bran)
• I only eat white meat and fish (not red meat)
• I regularly give blood*
• I cook using aluminium or enamel cookware (not stainless steel or iron)
• I frequently use antibiotics, aspirin or antacids (indigestion remedies)

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