Iron Supplements: What to Know Before You Start + Clues You May Have Low Absorption
What to Know Before You Buy
A friend recently reached out asking about iron supplements. She checks my blog first whenever she’s considering anything in the wellness aisle (🥹) and noticed I hadn’t covered iron yet. So, let’s fix that.
Iron is one of those nutrients that’s essential but often misunderstood. It’s not just about feeling tired; low iron levels can affect everything from mood to metabolism to immune function. But before you grab a bottle off the shelf, there are a few things you should know.
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Test, Don’t Guess
Iron supplementation should always start with lab work. You want to know your serum iron and ferritin levels. Ferritin is especially important. It is your iron storage marker, and it can be low even when serum iron looks okay.
If your ferritin is chronically low, that’s a sign your body isn’t storing iron well. This could be due to absorption issues, inflammation, or other underlying factors. Supplementing blindly can lead to iron overload (which is toxic) or missed root causes.
Iron optimal range: 80-100 mmol/dL regardless of sex.
Ferritin optimal range: 45-265 ng/mL (menopausal or assigned male at birth), 45-125 (menstruating).
What About Hemoglobin?
Hemoglobin is the iron-containing protein in red blood cells that carries oxygen throughout the body. When iron is low, hemoglobin production can drop, leading to symptoms like fatigue, shortness of breath, and brain fog.
But there’s nuance: You can have normal hemoglobin and still be iron deficient—especially if your ferritin is low. That’s why ferritin is often a more sensitive early marker, while hemoglobin reflects more advanced depletion.
Looking at all three (iron, ferritin, and hemoglobin) gives a fuller picture of your iron status and helps validate symptoms that might otherwise be dismissed.
Hemoglobin optimal range: 13.5-14.5 g/dL (assigned female at birth), 14-15 g/dL (assigned male at birth).
Food First (When You Can)
If your levels are just a bit low, food is your best ally. Iron-rich foods like steak, liver, lentils, and spinach are great, but they need a little help to be absorbed.
Pair them with vitamin C-rich foods like lemon, tomato, bell pepper, or berries. Think tart and tangy. Cooking your food in a cast-iron pan a few times a week can also add a small boost.
This approach works best when you’re in the “low-normal” (a.k.a. sub-optimal) zone and want to stay ahead of deficiency.
Choose the Right Supplement
Iron supplements are notoriously hard to absorb and can often cause stomach upset. If you need one, look for a high-absorption form like iron bisglycinate. Thorne makes a solid option that many people tolerate well.
If your levels are very low, especially ferritin, infusions might be the most effective route. That’s something to discuss with your healthcare provider.
Address Stomach Acidity
Low acidity in the upper digestive tract can make it hard for your body to access all the nutrients in your food. If you feel that your diet is reasonably high in iron, but your labs still fall short, exploring this further could be a great next step. Low stomach acidity has a few tells:
Low levels of nutrients like protein & albumin, vitamin D, chloride, phosphorus, zinc, magnesium, and B12 (although B12 markers may be unreliable for some).
Lower than optimal cholesterol levels (160-200 is the optimal range for total cholesterol). Your body may not be absorbing cholesterol and fats from the foods you eat.
Poop that appears greasy or floats. This can indicate that fats are not being broken down, which can be due to low stomach acidity.
Low pancreatic elastase. This may suggest poor digestive enzyme output and is often linked to low stomach acid.
H. pylori or other bacterial overgrowth. Stomach acidity is designed to kill invasive bacteria, and low levels are often insufficient to prevent the digestive tract from being colonized by these invaders.
Keep in mind that you don’t have to have all of these symptoms, but they are something to look for.
The good news is that low stomach acidity is fairly easy to address by taking 1-3 caps of digestive enzymes around your main meals. Although it may not make much of a difference right away, people also find relief by consuming small, acidic beverages (aperitifs) before meals as a way to cue bile production. Here is a recipe for one.
Timing and Pairing Matter
To get the most from your supplement:
Take it with vitamin C, either through whole foods, orange juice, or a vitamin C supplement.
Be mindful of blood sugar spikes if you are taking an iron supplement with juice.
Consider taking it around mealtime to reduce stomach discomfort.
Low stomach acid can impair absorption, so that’s worth exploring if you’ve had chronic issues.
Advocate for Yourself
If you’ve been dealing with low iron for a while, it’s worth finding a provider who will dig deeper. A good PCP or OBGYN can help uncover root causes, and a hematologist may be helpful if things get complex.
But don’t settle for care that feels dismissive. Your energy, mood, and long-term health are worth the extra effort it takes to find the right health care provider.
Final Thoughts
Iron is nuanced. It’s not just about popping a pill—it’s about understanding your body’s needs, supporting absorption, and getting the right care.
If you’re navigating this journey, I hope this post helps you feel more confident and informed. And if you ever have questions, you know where to find me.
