Recently, I’ve had a few friends feeling unwell after an iron infusion, and I’ve recommended they have their phosphate levels checked. Low phosphate (hypophosphataemia) is a relatively common side effect of iron infusions. Although it is usually mild and lasts only a few days, it can sometimes be dangerously low and persist for weeks to months.
Why Phosphate Matters
Phosphate is critical for many bodily functions, including energy production. Low phosphate levels can cause fatigue, weakness, muscle pain, and other symptoms. Iron infusions, especially the Ferric carboxymaltose type, can cause low phosphate by preventing the breakdown of a protein hormone called FGF-23.
The Role of FGF-23
FGF-23 is a protein hormone secreted by bones that acts on the kidneys to excrete phosphate. Normally, this process is controlled to keep phosphate levels normal. However, if FGF-23 cannot be degraded, phosphate levels will continue to be excreted even if they are already low. People who are malnourished are at higher risk of severe hypophosphataemia because their total phosphate stores are already low.
When to Consider Iron Infusions
There is definitely a place for iron infusions, such as after a major bleed, during pregnancy, or post-childbirth if you have anaemia (low haemoglobin). However, if your haemoglobin is still normal, and especially if the size of your red cells is normal (measured by MCV, which is reduced in iron deficiency), I would not recommend an infusion based on ferritin alone. Instead, aim to increase iron through dietary approaches or oral supplementation.
Tips for Taking Iron Supplements
If you take iron supplements, it’s best to take them every second day. This is because iron supplements increase a protein called Hepcidin, which decreases iron absorption as a protective mechanism to prevent iron overload. By skipping a day, Hepcidin levels decrease, and iron absorption improves. 😊