I'm in the middle of a long-form deep dive into iron metabolism in women — the first of a Substack series. And in the foundational research, I came across a critical difference in iron metabolism between men and women that I hadn't known about before. Or at least, it doesn't come up in our normal conversation around iron.

It’s yet another thing that we need to be aware of when we're talking about iron, and it yet again distinguishes the female body when we're talking about health and wellness, metabolism, and biological functioning compared to men.

A lot of the content around health and wellness, exercise, and optimization is for men, and we need to recognize that a lot of this isn't directly relevant to us, unfortunately.

It probably comes as no surprise that the canonical research that shaped how we think about iron — the decades of mechanism studies that built textbook physiology — was done largely in male animals and validated against male reference populations.

Early experiments deliberately standardized on male animals to avoid "cycle-phase variability." Unfortunately, for us women, this cycle-phase-variability complication is among the things that we need to understand to understand iron biology in women. This decision to focus on male biology ultimately means that reference-range studies drew on lab and hospital samples that skewed male.

The result is that the "default" picture of iron physiology that we learn may not fully describe women. We’re happily starting to peel back those layers.

Women lose iron through menstruation — about 10 to 15 mg per cycle. Heavy menstrual bleeding can triple the cycle loss.

The less obvious part is that women also absorb less iron per gram of diet than men do.

Testosterone suppresses hepcidin. And hepcidin is the liver hormone that stops iron from being absorbed in your gut.

Men generally have more testosterone than women. This means that at any given iron-status state, men's hepcidin floor sits lower than women's.

So when iron stores drop and the body is trying to refill, men's absorption ceiling is higher than yours would be in the same state.

You can't change the hormone setpoint. But the same hepcidin biology that explains the male-female gap also responds to what and when you eat. Here's how to work with it:

🍋 Add a vitamin C source: squeeze of lemon, red bell pepper, kiwi, citrus, berries. Vitamin C helps more iron cross your gut.

🥩 Get a heme iron meal in: beef, lamb, dark poultry, sardines, mussels, liver. Heme iron uses an absorption pathway less restricted by hepcidin, so it gets through more reliably than non-heme iron coming from plants.

💊 If you supplement iron, take it every other day. Every dose spikes hepcidin for ~24 hours, so alternate-day absorbs more total iron than daily.