Iron is one of those nutrients that rarely makes the news until something goes wrong. You feel inexplicably drained, your hair starts thinning, or a routine blood test flags a number you have never paid attention to. That number is usually ferritin — and it tells a more interesting story about your health than most people realise.
Ferritin is the protein your body uses to store iron. A single ferritin molecule can hold up to several thousand iron atoms, locking them away safely inside cells and releasing them when demand rises [1]. When a laboratory measures "serum ferritin" from a blood sample, it is reading a small fraction of the total that leaks into the bloodstream — but that fraction is the most practical window we have into how much iron your body is holding in reserve. A low number typically signals depleted stores; a high number may signal excess iron, or — because ferritin also rises during inflammation and infection — it may simply mean the body is dealing with something else entirely [2].
This dual nature is part of what makes ferritin fascinating, and occasionally frustrating, as a health marker. Getting it right matters, though, because the evidence is clear on one point: iron is a Goldilocks element. Both too little and too much are associated with worse health outcomes as we age.
Iron deficiency: the world's most common nutritional shortfall
Iron deficiency is not a niche concern. According to the Global Burden of Disease Study 2017, iron-deficiency anaemia was among the leading causes of years lived with disability worldwide [3]. It is particularly common among premenopausal women, pregnant women and young children [7].
An important distinction often missed is that you can have depleted iron stores — reflected by a low serum ferritin — well before your haemoglobin drops far enough to cross the clinical threshold for anaemia [1]. In other words, your body can be running low on iron while your full blood count still looks "normal".
Ferritin and fatigue: what the trials say
The most immediately noticeable consequence of low iron stores is fatigue — and this is one area where clinical trial evidence, not just observational data, exists.
A systematic review and meta-analysis of 18 randomised controlled trials, enrolling 1,170 adults who were iron-deficient but not anaemic, found that iron supplementation was associated with a significant reduction in self-reported fatigue (standardised mean difference −0.38; 95% CI −0.52 to −0.23) [4]. The effect was specific to subjective fatigue; objective measures of physical capacity, including maximal oxygen consumption, did not show a statistically significant improvement in the same analysis.
A more recent Cochrane-linked systematic review of randomised trials found that intravenous iron, compared with placebo, was associated with improved physical function and reduced fatigue scores in non-anaemic iron-deficient adults [5]. However, the quality of evidence was rated as low, and the authors cautioned that further, more robust studies are needed before firm conclusions can be drawn.
The practical takeaway is that if your ferritin is low and you are experiencing persistent tiredness, iron status is a reasonable thing to discuss with your GP — not because supplementation is always warranted, but because identifying and correcting genuine iron deficiency is one of the more straightforward interventions in medicine.
Iron and hair: what ferritin can (and cannot) tell you
Hair thinning sends many people to a blood test, and ferritin is often the first marker checked. The biological rationale is sound: hair follicle cells are among the most rapidly dividing in the body, and iron plays a role in DNA synthesis and cell proliferation within the follicle bulb [6].
A comprehensive review published in Dermatology and Therapy found that iron deficiency has been linked in some studies to telogen effluvium (the kind of diffuse shedding that follows a physiological stressor), alopecia areata, and androgenetic alopecia — but the evidence is mixed, and large, placebo-controlled trials are limited [6]. A clinical guide published in Cutis noted that while low serum ferritin is a highly specific and sensitive marker for iron deficiency, its role as a cause of hair loss (rather than a co-traveller) is not definitively established [2].
What can be said is that ruling out iron deficiency is a standard part of investigating unexplained hair loss, and that correcting documented deficiency — under medical guidance — is reasonable clinical practice. What cannot be said is that ferritin supplementation will regrow hair or that a specific ferritin level guarantees healthy hair. A 2006 review in the Journal of the American Academy of Dermatology put it plainly: there is currently insufficient evidence to recommend universal screening for iron deficiency in all patients with hair loss, and the decision should be based on clinical judgement [7].
The other side of the coin: when iron is too high
If low iron is a well-known problem, high iron is a quieter one — but the ageing evidence makes it equally worth understanding.
A systematic review and meta-analysis of 11 prospective studies found that higher body iron stores, measured by serum ferritin, were significantly associated with a greater risk of type 2 diabetes (pooled relative risk 1.70; 95% CI 1.27–2.27, comparing highest versus lowest ferritin categories) [8]. The association was modestly attenuated but still significant after adjustment for inflammatory markers. Higher heme iron intake (predominantly from red and processed meat) showed a similar pattern.
The mechanism is not fully understood, but researchers have hypothesised that excess iron may contribute to oxidative stress in insulin-producing cells and promote insulin resistance [8]. This is not a reason to avoid iron-rich foods wholesale — it is a reason to recognise that, unlike many nutrients, iron does not follow a "more is better" logic.
Iron, ageing and the genetics of longevity
The most intriguing piece of the ferritin story comes from genomics. In 2022, a genome-wide meta-analysis of up to 257,953 individuals in the HUNT, MGI and SardiNIA cohorts used Mendelian randomisation — a method that uses genetic variants as natural experiments — to examine the causal relationship between iron biomarkers and mortality. The analysis found evidence of a harmful effect of genetically elevated serum iron and transferrin saturation on all-cause mortality, while there was weak evidence of a protective effect of increasing serum iron only at the very low end of its distribution [9]. In other words, the genetic evidence is consistent with a picture where moderate iron levels are associated with the best outcomes, and the risk rises at both extremes.
This echoes a landmark multivariate genomic study that combined data on healthspan, lifespan and longevity to identify genomic loci influencing all three ageing phenotypes. Among the pathways the researchers implicated was haem metabolism — the biological machinery that processes the iron-containing molecule at the heart of haemoglobin [10]. The authors noted that genes enriched in their analysis overlapped with known ageing pathways including the response to DNA damage, apoptosis and cellular homeostasis.
Reading your ferritin: what to know
Ferritin is a standard item on many blood panels, but interpreting it requires context.
Low ferritin is a strong indicator of depleted iron stores. If symptoms like fatigue, breathlessness on exertion, or hair shedding are present alongside a low reading, it is worth discussing with a GP, who may investigate the underlying cause (diet, absorption, blood loss) before considering whether supplementation is appropriate [1].
High ferritin is harder to interpret. Because ferritin is an acute-phase reactant, it rises during infection, inflammation, liver disease and other conditions [2]. A single elevated reading does not necessarily mean iron overload — it means further investigation may be warranted, including transferrin saturation and, in some cases, genetic testing for hereditary haemochromatosis (the most common genetic cause of iron accumulation in people of European ancestry) [1].
"Normal" ferritin does not always mean optimal. Laboratory reference ranges are wide, and a reading at the lower end may still leave someone genuinely symptomatic even though it falls within the "normal" band [4]. This is one area where clinical context and symptoms matter as much as the number — your GP is best placed to interpret your result in the context of your health.
The bigger picture: iron as a longevity signal
What makes ferritin interesting from an ageing perspective is that it sits at the intersection of energy, metabolism, inflammation and oxidative stress — all pillars of how the body ages. The evidence does not point to a single ideal ferritin number that guarantees healthy ageing. Instead, it paints a picture of a marker where the direction of trouble runs both ways: too low, and the body lacks the raw material for oxygen transport and cellular energy; too high, and the surplus may contribute to oxidative damage and metabolic disruption [8][9].
Tracking ferritin over time — alongside other markers — gives a more complete picture of how your body is managing one of its most fundamental resources. If you are curious about where your iron stores sit, a ferritin blood test is one of the simplest and most informative starting points. Understanding the number is the first step; what to do about it is a conversation for you and your GP.
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- GBD 2017 Disease and Injury Incidence and Prevalence Collaborators. Global, regional, and national incidence, prevalence, and years lived with disability for 354 diseases and injuries for 195 countries and territories, 1990–2017. Lancet. 2018;392(10159):1789–1858. doi:10.1016/S0140-6736(18)32279-7 (PMID: 30496104)
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- Dugan C, Cabolis K, Miles LF, Richards T. Systematic review and meta-analysis of intravenous iron therapy for adults with non-anaemic iron deficiency: an abridged Cochrane review. Journal of Cachexia, Sarcopenia and Muscle. 2022;13(6):2637–2649. doi:10.1002/jcsm.13114 (PMID: 36321348)
- Almohanna HM, Ahmed AA, Tsatalis JP, Tosti A. The Role of Vitamins and Minerals in Hair Loss: A Review. Dermatology and Therapy. 2019;9(1):51–70. doi:10.1007/s13555-018-0278-6 (PMID: 30547302)
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