Low iron can cause fatigue in women, and reasons why this treatable condition is so often missed

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There’s a lot of reasons why someone may complain of undue fatigue, but there’s a few things that tend to recur. One thing worth looking out for, especially in women, is iron deficiency. Monthly blood loss is a major risk factor for this, obviously, especially if coupled with a diet low in properly iron-rich foods such as red meat and liver. It’s a common problem, and one that is often easily resolved. The problem is it tends to go unrecognised.

A fundamental reason for this, which I describe in this blog post, is that we doctors tend in women to think that fatigue is often caused by anaemia (low levels of the red blood cell pigment haemoglobin that carries oxygen around the body and delivers it to tissues). So, when we see a woman of childbearing age, anaemia is often thought of. Often, though, a blood test will not reveal anaemia as defined by ‘normal’ blood levels.

The normal range of haemoglobin is lower in women than in men. One reason for that might be that women of reproductive age are generally losing blood each month. I remember one of my tutors questioning the wisdom of having a haemoglobin normal range for women lower than that for men. He suggested that we might be simply letting many women be ‘a bit anaemic’.

But even leaving this (I think, valid) thought aside, another problem with checking for anaemia only is that iron deficiency can occur in the absence of anaemia. So, while iron deficiency is a very common cause of anaemia (especially in women), just because a woman is not anaemic does not mean she is not low in iron. And iron deficiency, even in the absence of anaemia, can cause fatigue and other symptoms such as low mood.

Because of this, it makes sense to check for iron levels too. There are several iron-related tests, and the one I’ve found to be most useful for judging overall iron levels in the body is something known as the serum ‘ferritin’ level. However, even when this test is done, we have other problems relating to its interpretation.

This issue relates again to the concept of ‘normal ranges’. Generally, normal ranges encompass 95 per cent of people. That means to have a ‘low’ or ‘high’ reading someone has to be in the bottom or top 2.5 per cent of the population. Some might argue (as I would) that this means to be ‘abnormal’ you have to be really very abnormal, and maybe it would make sense to make the ‘normal’ range narrower.

The normal range for ferritin in women is often about 12-150 ng/ml. That looks quite wide, doesn’t it? Someone with a ‘normal’ ferritin of 12 or 20, say, will still be very much down the low end of the scale, and perhaps be suffering as a result of their low iron.

We do have some evidence that this indeed may be the case in the form of a study which was published this week [1]. Almost 200 women aged 18-53 suffering from fatigue were included in the study. All of them were non-anaemic (haemoglobin levels 12.0 g/dL or more) and had ferritin levels lower than 50 ng/ml. The women were treated with ferrous sulphate (the form of iron most commonly prescribed by doctors) or placebo for a total of 12 weeks.

In the women taking iron, fatigue scores dropped by about half. There was a drop in fatigue scores seen in those taking placebo too, but to a lesser extent. The greater improvement in those taking iron was statistically significant.

This study provides at least some evidence that just being in the ‘normal range’ for iron levels (ferritin) is not enough. I’ve found in practice that, as this study suggests, ferritin levels should be above about 50 ng/ml for someone to feel properly energised.

The form of the iron used in this study (ferrous sulphate) is the last form of iron I’d use in practice, though. It’s generally difficult for the body to absorb this form of iron, and it’s often irritant to the gut and often causes constipation. My preferred form of iron is actually the brand Floradix in liquid form. I find this usually does an efficient job of picking up someone’s iron levels (and energy) where appropriate.


1. Vaucher P, et al. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ. 2012 Jul 9. [Epub ahead of print]

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