I was quickly moving along through my busy university
clinic, seeing another CKD patient when the nurse came to inform me that
the patient’s hemoglobin was critically low at 5 g/dl, while the patient
appeared to be just fine. I reviewed the rest of labs just to find out
that the iron studies were even more impressive: iron saturation 3% and
ferritin 2 ng/ml.
I inquired about the usual suspects - bleeding from various
sources - but no luck there (the patient was post-menopausal and denied GI
bleeding, later ruled out by EGD and colonoscopy)... Failing to identify a
cause of her iron deficiency, I presented the case to my staff who, a fter reviewing the data, asked me an unusual question: does
she drink tea? To my surprise, indeed, the patient admitted to drinking large
quantities of black tea. Still puzzled about the link between the two, I jumped
onto Google Scholar.
In the renal world, the only time when we talk about tea is
when discussing hyponatremia in patients that are on a “tea and toast” diet. So what did I find out? An interesting South African study demonstrated that black
tea inhibits non-heme iron absorption by forming iron tannate complexes. This
was confirmed by a UK study which showed that black tea
was the most potent out of all polyphenol-rich beverages (coffee, cocoa, etc.)
in inhibiting absorption of non-heme iron.
Iron deficiency anemia is common in CKD patients, one of the
latest mechanisms to be described involves the hepcidin-ferroportin axis (as
recently reviewed in JASN).
But today I discovered another one!