If you're constantly tired, low ferritin is one of the first things worth ruling out. It's the most common nutrient deficiency in the world, affecting an estimated 1 in 4 women of reproductive age in the UK — yet most people who feel "just a bit drained" never get it tested.
What is ferritin?
Ferritin is a protein that stores iron in your body's cells. Think of it as your iron savings account. When your iron intake from food drops or your body needs more (during periods, pregnancy, intense training, or recovery from illness), you draw on these stores.
A blood test for ferritin tells you how full those stores are — long before your haemoglobin (the iron in your blood) starts to drop. That's why ferritin is the most sensitive early marker of iron status: it falls first, often months before clinical anaemia sets in.
Why does ferritin matter?
Iron does far more than carry oxygen in red blood cells. It's involved in:
- Energy production in every cell (your mitochondria need iron to produce ATP)
- Cognitive function — brain fog and difficulty concentrating are classic low-iron symptoms
- Immune function — low iron increases infection risk
- Hair growth — chronic low ferritin is a leading cause of unexplained hair shedding
- Exercise capacity — even mild iron deficiency reduces endurance and recovery
According to NHS guidance, women aged 19-50 need around 14.8 mg of iron daily — and many fall short. Vegetarians, vegans, endurance athletes, blood donors, and anyone with heavy periods are at higher risk.
What do the numbers mean?
Ferritin is reported in micrograms per litre (μg/L). UK reference ranges:
- Below 15 μg/L — iron deficiency
- 15-30 μg/L — depleted stores (often symptomatic)
- 30-200 μg/L — typical for women
- 30-300 μg/L — typical for men
- Above 300 μg/L — high (worth investigating; ferritin rises with inflammation and certain genetic conditions like haemochromatosis)
Many functional medicine practitioners argue that ferritin between 15-50 μg/L is "borderline" and often symptomatic, even though it falls within the lab's "normal" range. If you feel tired and your ferritin is at the bottom of the range, it's worth acting on.
Three things you might not know about ferritin
1. Inflammation can mask iron deficiency
Ferritin is what's called an "acute-phase reactant" — it rises during infection, injury, or chronic inflammation. So someone with both inflammation AND iron deficiency can have a misleadingly normal ferritin reading. That's why a full iron panel — including transferrin saturation and total iron binding capacity (TIBC) — gives a clearer picture than ferritin alone.
2. Coffee and tea block iron absorption
Tannins in tea and coffee can reduce iron absorption from food by up to 60%. If you're trying to raise low iron through diet, the simplest fix is to wait at least an hour between meals and your morning brew.
3. Vitamin C dramatically boosts plant iron absorption
Plant-based "non-heme" iron (from beans, lentils, leafy greens) is harder to absorb than the "heme" iron in red meat. Adding Vitamin C — a squeeze of lemon, peppers, citrus, kiwi — to a meal can increase iron absorption from plants by 3-6 times.
Best food sources of iron
Heme iron (better absorbed):
- Red meat, especially liver
- Sardines, mackerel, mussels
- Chicken thighs (more iron than breast)
Non-heme iron (pair with Vitamin C):
- Lentils, chickpeas, kidney beans
- Spinach, kale, beetroot leaves
- Pumpkin seeds, cashews
- Fortified breakfast cereals
- Dark chocolate (genuinely)
How to test your ferritin and iron
Ferritin is included in our Iron Status panel — which also covers transferrin, transferrin saturation, total iron binding capacity, and serum iron for a complete picture. It's also bundled into our Anaemia Profile and the broader Standard Screen.
Visit our County Durham clinic or a UK partner clinic — results in 3-5 working days as a clear PDF report. If your ferritin is low, the next step is usually 8-12 weeks of supplementation followed by a retest. The change you'll feel often surprises people.
Browse our blood count and iron panels →
This article is informational. Chxhealth is a biomarker and genetic data provider — we do not diagnose, treat or prescribe. If your results are outside typical ranges, talk to your GP or a healthcare professional about next steps.