Ferritin: What your test result actually shows, and why both low and high can matter
Ferritin is the marker that tells you what's actually in your iron stores, not just what's circulating in your blood right now. It's also one of the most misunderstood results on a blood test, since both a low reading and a high one can be telling you something important, and they don't mean the same thing.
What ferritin actually is
Ferritin is the protein that stores iron in your body. While a standard iron test only shows what's circulating at that exact moment, which can vary through the day, ferritin is much more stable and reflects your overall reserves. That makes it a far more reliable way to understand your iron status, and it's usually the first marker to drop as deficiency develops, often well before anaemia shows up on a full blood count.
This is also why ferritin and haemoglobin can tell two completely different stories. You can have entirely normal haemoglobin while your ferritin, and your body's actual iron reserves, are already significantly depleted. Haemoglobin is what your body protects until the very end, ferritin is what it draws on first.
Why low ferritin matters, even without anaemia
Low ferritin can sit behind fatigue, low mood, poor focus, hair thinning, restless legs and reduced exercise tolerance, all before it progresses to anaemia. If you've had symptoms like these with bloods that came back "normal," it's worth checking whether ferritin was actually included.
It's also worth knowing that the standard "normal" range is not the same as the optimal range. Most lab reference ranges start as low as 12 to 15, a threshold built to catch anaemia, not to reflect how well your thyroid, hair follicles or brain are actually functioning. Hair shedding, for example, often starts when ferritin drops below 70, well before it's flagged as anything to worry about on a standard result. See the chart below for more detail on standard versus optimal ferritin ranges.
The symptoms tend to show up at the tissue level long before they show up on a lab report: cold hands and feet even in a warm room, hair shedding in the shower, fatigue that sleep doesn't touch, brain fog that comes and goes, and poor recovery after fairly light exercise. These are worth paying attention to even when your ferritin technically sits inside the reference range.
What can cause low ferritin levels
There's more than one reason ferritin runs low, and it's rarely just because you’re not eating enough iron-rich foods. Blood loss is the most common driver in women, particularly heavier or more frequent periods, but low iron intake matters too, especially with plant based diets or simply eating less overall, including from appetite suppressing medications like GLP-1 drugs, which can reduce how much iron makes it into your diet in the first place.
Protein matters here too, and it's easy to overlook. Your body needs protein to make transferrin, the protein that transports iron around your body, so if you're not eating enough of it, even a reasonable iron intake can struggle to be transported and stored properly.
Absorption is just as important as intake, though, and this is the part that gets missed most often. Low stomach acid, long-term PPIs, too much caffeine, coeliac disease, and other gut conditions can all limit how much of the iron you eat actually gets absorbed, regardless of how well you're eating. Chronic inflammation adds another layer on top of this, since it raises a hormone called hepcidin that directly blocks iron absorption in the gut, which is why some people's ferritin stays stubbornly low no matter how much iron they take.
If you also carry an MTHFR gene variant, low ferritin can compound things further. MTHFR affects methylation, which supports neurotransmitter production and how well your body regulates inflammation, so when ferritin is low at the same time, both systems are under pressure together, and symptoms tend to reflect both.
Why high ferritin isn't automatically good news
This is the part that catches people out. A high ferritin result doesn't necessarily mean your iron stores are healthy, it can also be a sign of inflammation. Ferritin behaves as what's called an acute phase reactant, meaning your body raises it as part of an inflammatory response, separate from how much iron you actually have. This is why ferritin should always be read alongside inflammation markers, rather than on its own, to understand what's actually going on.
High ferritin is also worth ruling out for a genetic condition called haemochromatosis, which can affect 1 in 150 people, where the body absorbs too much iron and stores build up over time, usually checked alongside a transferrin saturation test to tell it apart from inflammation driven high ferritin.
A high or a low ferritin result both deserve a proper look, not just a glance at whether the number falls inside the reference range.
Ferritin levels at a glance: NHS range versus what we look for
Ferritin (µg/L) | Standard NHS range | Optimal ranges we look for |
Below 13 | Flagged as iron deficient, especially alongside anaemia | A clear priority to address |
13 - 30 | Technically within range | Often where fatigue, hair shedding and brain fog still show up |
30 - 50 | Within range | Improving, though some women remain symptomatic |
50 - 100 | Within range | Generally where we aim for, for energy, mood, hair and thyroid function |
100 - 150 | Upper end of range | Usually fine, unless symptoms suggest otherwise |
Above 150 | Flagged as high | Worth investigating for inflammation or haemochromatosis, alongside a transferrin saturation test |
Exact thresholds vary slightly between labs, so use this as a general guide alongside your own symptoms and your practitioner's interpretation, not as a diagnosis on its own.
When ferritin levels won't budge, despite doing everything right
For some people, low ferritin persists even with a good diet and supplementation. This is often where the gut comes in. Emerging research points to a strong connection between gut health and iron absorption, involving a liver hormone called hepcidin, which controls how much iron your gut is able to absorb in the first place. Inflammation, including inflammation driven by an imbalanced gut microbiome, can raise hepcidin and effectively block iron absorption, regardless of how much iron you're taking in.
Reduced levels of beneficial gut bacteria, particularly the kind that produce short chain fatty acids like butyrate, have also been linked to lower iron absorption and gut lining changes that make this harder to correct.
In other words, if your gut health is off, it can directly limit how much of the iron you're eating or supplementing actually gets used.
What actually moves ferritin in the right direction
Getting ferritin to shift usually comes down to a few specific things working together, rather than iron alone:
Enough protein at every meal, aim for at least 20-30g, since protein supports the digestive and absorptive processes iron depends on
Pairing iron rich foods with a source of vitamin C, which meaningfully improves absorption
Addressing gut inflammation directly, rather than just adding more iron on top of it
Keeping blood sugar steady, since swings raise cortisol and increase your body's nutrient demands at the same time
Targeted iron supplementation, once gut function has actually improved, so it has a proper chance of being absorbed rather than passing straight through.
Choosing the right iron supplement
Not all iron supplements work the same way, and getting this part wrong is one of the most common reasons people give up on iron before it's had a real chance to work.
Liquid iron is often marketed as the gentle option, and it can be easier on the stomach, but many liquid formulas contain a much lower dose of elemental iron than tablets or capsules, so they're not always strong enough to actually shift a low ferritin on their own.
Iron bisglycinate is our supplement of choice, a well absorbed, gut friendly form that tends to cause far less constipation than other types. Even so, we usually recommend starting low, sometimes just once a week, and building up gradually from there rather than jumping straight to a daily dose. If constipation does show up, that's a sign to reduce the dose, not push through it.
Ferrous fumarate is what's most commonly prescribed by GPs, and while it's effective, it can be genuinely hard on the stomach, causing nausea, constipation or stomach pain for a lot of people, which is often why iron supplementation gets abandoned altogether.
For some people, particularly where gut inflammation is part of the picture, lactoferrin can work better than a standard iron supplement. Rather than delivering free iron directly, it works by binding iron in a way that supports absorption while also calming gut inflammation, which can make it a gentler, and for some, more effective option.
What to do if your ferritin doesn't add up
If your ferritin is low, high, or simply doesn't match how you feel, it's worth looking at the full picture rather than the single number. At Urban Wellness we offer comprehensive blood tests that iron and ferritin, so you're looking at the full picture rather than one piece in isolation.
Get in touch if this sounds familiar, we can help you get underneath the number and work out what's actually going on.
References
Correnti M, Gammella E, Cairo G, Recalcati S. Iron absorption: molecular and pathophysiological aspects. Metabolites. 2024;14(4):228.
Seo H, Yoon SY, ul-Haq A, et al. Effects of iron deficiency on the gut microbiota and intestinal barrier function: implications for host-microbe interactions. Nutrients. 2023;15(3):691.
