The iron block!

I recently saw a delightful patient who had been prescribed 300 mg of iron daily by her doctor, yet her serum iron levels were not increasing. Why?

Firstly the type of iron prescribed dictates its ability to be absorbed. Many anaemic women are automatically prescribed ferrous sulfate, very poorly absorbed, often causing constipation and dark stools. The best type of iron to take if anaemic is iron in a bisglycinate form in a formula which also contains folate, B12 and vitamin C. This will ensure maximum uptake in the small intestine.

Be aware that more is not necessarily better due to a mechanism called the mucosal block. This is when an initial dose of iron can reduce the subsequent dose. Studies have been conducted on 20 mg, 30 mg and 60 mg as the blocking dose. Researchers found that a 20 mg dose of iron did not consistently have an effect on a subsequent dose of iron.

However, 30 mg and 60 mg blocked the subsequent 10 mg dose given 12–24 hours later either completely or by up to 46%.
So we can understand that a 300 mg daily dose would have a significant effect on absorption, with the mucosal block constantly switched on.

Further, a Cochrane Review concluded that intermittent dosing is just as effective as daily dosing at reducing anaemia and iron deficiency and improving the concentration of haemoglobin and ferritin with no side effects.

The side effects of taking the incorrect type of iron supplementation are the result of the unabsorbed fraction of the iron that remains in the gastrointestinal tract, producing free radicals that eventually create inflammation and affect the gut microbial composition and also produce symptoms such as nausea and constipation.