Physical activity found to reduce iron levels in women, and why it’s important to correct this

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Nutritional needs can vary a bit between men and women, and this does certainly seem to be generally so for iron. Women who menstruate are at risk of iron deficiency because of the iron lost in menstrual blood each month. In my experience, a very significant proportion of such women have low or suboptimal iron levels. This can lead to all sorts of issues including anaemia (iron deficiency anaemia). However, even in the absence of anaemia, low iron levels can affect physical and mental energy. Unfortunately, for reasons that I describe here, low iron status is often missed, and this can lead to a lot of unnecessary suffering.

Menstruation is not the only risk factor for iron deficiency. Others include being vegetarian, and engaging in physical activity. Being vegetarian generally makes it much harder for individuals to get adequate amounts of the form of iron most readily absorbed by the body (known as ‘haem’ iron, and found in animal products such as meat). The link between iron deficiency and exercise is less obvious. However, quite intense physical exercise can induce some bleeding in the gut or kidneys that can contribute to iron loss. I remember talking to a marathon running doctor some years ago who told me that there is a belief in the running community that the impact of the foot on the ground/footwear during running is enough to destroy red blood cells and contribute to blood loss. Appreciable amounts of iron can even be lost in sweat.

This issue is particularly important for female athletes and any other women who are perhaps more active than most mere mortals. For example, women in the military often engage in quite strenuous exercise, and the resulting iron deficiency or possibly even anaemia can have profound effects on their physical and mental energies and wellbeing.

In a study published on-line last week in the American Journal of Clinical Nutrition, iron status was assessed in a group of 219 female soldier volunteers (average age 20) just before embarking on an 8-week basic combat training course [1]. Women with iron deficiency were identified. If a woman was iron deficient also had a haemoglobin level of less than 12 g/dL, she was diagnosed with ‘iron deficient anaemia’.

At the beginning of the course, women were also assessed in terms of their physical and mental functioning. This came in the form of a 2-mile timed run, and a mood state questionnaire which assessed mental factors such as vigour, tension, depression and anger. At the start of the course, women in all groups (normal, iron deficient, those with iron deficiency anaemia) were selected (randomly) to received either iron supplementation (100 mg of iron sulphate a day) or placebo. The women were assessed at the end of the course in terms of their iron and blood status, as well as their physical and mental function.

Overall, it was found that the basic combat training course led to a significant decline in iron status, supporting the idea that physical activity is a risk factor for iron deficiency. Perhaps not surprisingly, giving iron in supplement form reduced the extent of the iron loss during the course.

Taking the group as a whole, the iron supplementation led to an improvement in ‘vigour’ as it relates to mental function. Also, iron supplementation led to an improvement in the 2-mile timed test in women who started out with iron deficient anaemia (though this effect was not seen in ‘normal’ women or those with iron deficiency only).

What this study does, I think, is remind us of the need for assessing iron and blood status in women of menstruating age, particularly those at risk of iron deficiency and anaemia. But I’d also like to reiterate a couple of points I’ve made before:

1. The normal range for iron levels is set very wide, which can mean that even individuals in the normal range have suboptimal iron and can suffer as a result. I tend to favour ‘ferritin’ for assessing iron status, and in this study the cut-off used to determine deficiency was a level of 12 mcg/L. My experience in practice leads me to conclude that levels really need to be above 50 for individuals to enjoy optimal energy and wellbeing

2. Iron supplements come in different forms. The standard issue used in medicine (and in this study) is iron sulphate (also known as ferrous sulphate). The problem is, this is not a particularly absorbable form of iron. I have seen many, many individuals really struggle to get their iron levels up with this form of iron. My preferred form of iron in practice is a liquid form of iron going by the name of Floradix.

One final thing, just with everything else, while a bit of something may be good, too much may not. This is certainly true of iron. Which means that iron is not a nutrient to be supplemented with willy nilly in my opinion. I recommend that ferritin levels be checked to determine a need for iron, along with re-checks every few months to ensure there has been adequate response to treatment and that iron levels do not become excessive.


1. McClung JP, et al. Randomized, double-blind, placebo-controlled trial of iron supplementation in female soldiers during military training: effects on iron status, physical performance, and mood. Am J Clin Nutr 27th May 2009 [epub ahead of print publication].

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