First of all, a quick recap of Part 1:
A) Iron Deficiency Anemia (IDA) is when iron shortage makes your blood unable to carry adequate oxygen from your lungs to all the cells that need it,
B) it causes a lot of the same symptoms as POTS,
C) 50% of respondents in the POTS Patient-Powered Survey reported they'd had iron deficiency anemia, and
D) the normal prevalence in American adults is 1% for men, 9-12% for white non-Hispanic women, up to 20% for African-American or Mexican-American women, and only 3% for non-pregnant women .
50% seemed awfully high, and my first reaction was to wonder if our POTS Patient-Powered Survey had mangled that question. I thought maybe it led readers to confuse iron deficiency anemia with something more mild, like their doctor suggesting iron supplements just because of heavy periods or whatnot. I checked and the question read "Have you ever had iron deficiency anemia?" Not too confusing. Plus, after receiving copious feedback from Part 1 of this blog post, I realized that our respondents seemed very knowledgable about IDA. At least among those who cared to comment, they were familiar with the blood tests and various ways to treat it (e.g., several had tried iron infusions), and I decided maybe the 50% was accurate. Granted, self-report data is always considered weak compared to how the CDC collected their IDA data (i.e., they sent teams house-to-house drawing blood from people!) but I decided to entertain the possibility that our responses were accurate and started searching for explanations.
Low iron in POTSies has been observed before. A study by Jarjour & Jarjour  found that children with POTS had higher rates of iron deficiency than non-POTS children. Below are their findings for three different measures of low iron.
Children with POTS, 50%, purple Normal US pediatric population, 14%, purple
Teenage girls with POTS, 25%, red Teenage girls in normal US population, 9%, red Teenage boys with POTS, 16%, blue Teenage boys in normal US population, 1%, blue
Teenage girls with POTS, 18%, red Teenage girls in normal US population, 1.5%, red Teenage boys with POTS, 43%, blue Teenage boys in normal US population, .1%, blue
In all three studies, they found that the young POTS patients had significantly higher prevalence of iron deficits.
What's more, this Boston University School of Medicine research poster suggests that gut malabsorption leads to iron deficiency, which then contributes to POTS. In their research, they found that people with low ferritin levels had 2.8 times the odds of having POTS . They also found the following difference in mean ferritin levels between POTS patients and the control group:
Patients with POTS, 37.1 ng/mL Patients without POTS, 57.8 ng/mL
So iron storage levels were lower in adult POTS patients also. But could it really just be a case of malabsorpton, like the BUSM poster suggested? As a nutritionist, I've seen loads of people with terrible digestion, and very few of them report iron deficiency anemia. So I googled further and found this super-impressive research study done by Dr. Raj et al. They brought POTS patients and control subjects into their clinic, put them on a sodium-controlled diet for a couple days, then gave them a tilt table test while taking blood every few minutes. They learned a lot of things, but among them was that POTS patients had low red blood cell volume that was commensurate with their depletion of blood plasma . They suggested that low red blood cell volume may be caused by low erythropoietin levels - the renal hormone that triggers red blood cell production in bone marrow - perhaps because kidneys regulate red blood cell volume to match the low plasma volume. If this is the case, it's a kidney thing.
So, like everything with POTS, it's complicated. If it's a kidney issue, then it seems that iron deficiency isn't the root problem. Of course, there could be issues both with IDA from iron malabsorption, as the BUSM poster suggested, and also kidney hormones, as Dr. Raj et al suggested. I wouldn't be surprised if multiple mechanisms are at play: The more I learn about POTS, the more amazed I am at how it can drum up so many different ways to deny our bodies good circulation!
Perhaps the most promising news is that Mayo clinic is recruiting volunteers for clinical trials, where they plan to give iron infusions to adolescent POTS patients, then see if they improve on a tilt table test .
So, how can we use this to feel better? In addition to getting my iron checked and discussing supplements with my doctor, I'm thinking I will re-commit to elevating the head of my bed again. My doctors recommended it last year, to increase plasma volume, but I found it uncomfortable. But perhaps if it helps raise plasma volume, it also encourages the kidneys to release more erythropoietin, thereby increasing red blood cell volume. This is me speculating wildly, so make sure to ask your doctors before you do anything.
This is all fascinating stuff, so if you have insights, please share them. You can contact us here. Please consider taking the POTS Patient-Powered Survey. More data means we can do better analyses. You can read more or take it here. Be well!