I have a myriad of reasons for my fatigue, shortness of breath, lack of motivation, headaches, lack of concentration, feeling very cold in my feet/hands, etc. (I have hypothyroidism, PCOS, fibromyalgia, asthma, migraines, & adult ADD -- I'm actually taking meds for each of these conditions too). However, I've been feeling a sharp intensity in the above symptoms, which is why I went to my GP. Long story short, I have yet another reason contributing to the above symptoms: iron deficiency. My TSH (thyroid levels) were fine, but my ferritin levels are at 21 ug/L. How low is this? Would this explain the above symptoms?

Of course, as soon as I muster enough energy, I'll walk to the nearest pharmacy and get iron supplements. However, I'm wondering... How long does it take for iron supplements to impact my health at all? Will I notice improvements immediately? Or is it more of a gradual thing that takes weeks before noticing more energy and focused concentration, etc? (Don't worry, I'll be taking it long-term... I'm just wondering if I'll see improvements fairly quickly as I have my Oral Exams -Grad School- in 6 days, and want my brain to be in tip-top shape).

1 Answer 1


Ferritin levels of 21 ug/L are on the extreme lower edge of the normal range. You can think about iron stores as follows. A healthy person will have iron stores of a few grams. Since iron is present in every cell of the body, we lose iron via the loss of dead skin cells, mucus, sweat etc. etc. The iron in red blood cells is recycled when they die, so we don't lose that iron. But you can lose iron due to bleeding, e.g. intestinal bleeding can go unnoticed and only cause low iron levels. Women who get heavy menstrual bleeding can also end up with low iron levels.

The typical loss of iron in healthy persons is about 1 milligram per day, this means that we absorb about 1 milligram of iron from food. The typical diet contains 10 to 20 milligrams of iron, our bodies are capable of absorbing quite a bit more than the 1 milligram and will typically be able to do that when iron stores get low unless, of course, the cause of the iron deficiency is due to poor iron absorption or a poor diet.

Iron supplements prescribed by a doctor typically contain about 100 milligrams of iron. You'll be able to absorb anywhere between 20% and 50% of this, so it will take at least a month before you've put back 2 grams of iron into your body. Without such supplements, with a good diet this would take ten times longer, so at least a year or so (assuming that the dietary fix is actually going to do the job).

Since you are young person (you're not an old, frail, 90 year old) you have to consider the cause of the iron deficiency even if it isn't due to serious medical problems. If it's due to a poor diet (as opposed to heavy menstrual bleeding), then your diet must be so poor that it's likely affecting your health in other ways besides causing low iron levels. If you were 90 years old then it would be far more reasonable that a normal diet could fall short of the iron requirement.

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