Iron and Circadian Rhythm

IRP1/IRP2 and the Circadian Clock

Iron regulatory proteins are not static sensors — they oscillate with daily rhythms, creating a direct molecular link between iron metabolism and the circadian system.

IRP1: The Bifunctional Iron/Aconitase Sensor

Dib L et al. "Diurnal control of iron responsive element containing mRNAs through iron regulatory proteins IRP1 and IRP2 is mediated by feeding rhythms." Genome Biol. 2024;25:138. PMID: 38773499

• High-amplitude diurnal oscillations in IRP1 and IRP2 regulation of IRE-containing transcripts
• Maximal IRP activity at the onset of the dark phase (active period)
• Key discovery: diurnal regulation of IRE-containing mRNAs can continue without a functional circadian clock as long as feeding is rhythmic
• This means feeding patterns are the primary driver, not the molecular clock itself

IRP1 has a dual function:

• Iron-replete: IRP1 binds a [4Fe-4S] cluster and functions as cytosolic aconitase (enzyme)
• Iron-depleted: IRP1 loses its iron-sulphur cluster and binds IREs on mRNA (regulatory function)

This switching between enzyme and RNA-binding protein is itself rhythmic — oscillating with feeding/fasting cycles.

Clock Gene Regulation of IRP2

The Ireb2 gene (encoding IRP2) is circadianly transcribed through BMAL1:CLOCK heterodimers in certain tissues

• BMAL1 and CLOCK are core circadian clock transcription factors
• They drive rhythmic IRP2 expression, which then rhythmically regulates transferrin receptor (TFRC) mRNA stability
• This creates a direct link: clock genes -> IRP2 -> iron uptake regulation

flowchart TD
    A[BMAL1:CLOCK] --> B[IRP2 Transcription]
    B --> C[IRP2 Protein]
    C --> D[IRE Binding on mRNA]
    D --> E[TFRC Stability]
    D --> F[Ferritin Translation]

    G[Feeding Rhythm] --> H[IRP1 Oscillation]
    H --> I[Aconitase / RNA-binding Switch]
    I --> D

    E --> J[Circadian Iron Uptake]
    F --> J
    J --> K[Normal Iron Gene Cycling]

    L[Iron Overload] --> M[Constitutively High Iron]
    M --> N[Blunted IRP Cycling]
    N --> O[Flattened Iron Oscillation]
    O --> P[Disrupted Clock Gene Feedback]

    L --> Q[Tryptophan Hydroxylase Disruption]
    Q --> R[Impaired Serotonin Synthesis]
    R --> S[Reduced Melatonin Production]

    P --> T[Poor Sleep Architecture]
    S --> T
    T --> U[ADHD Circadian Dysfunction]
    T --> V[ASD Sleep Disruption]

    classDef clock fill:#aed6f1,stroke:#2980b9,color:#0a1929
    classDef damage fill:#f1948a,stroke:#c0392b,color:#1a0505
    classDef outcome fill:#f7dc6f,stroke:#b7950b,color:#1a1400

    class A,B,C,D,E,F,G,H,I,J,K clock
    class L,M,N,O,P,Q,R,S damage
    class T,U,V outcome

Iron-Dependent Neurotransmitter Synthesis and Circadian Rhythms

Iron is a cofactor for three hydroxylases that synthesise circadian-relevant neurotransmitters:

DelRosso LM et al. "Iron deficiency across neurodevelopmental disorders." Children. 2026;13(2):180. PMC12938977

• Iron-dependent enzymes catalyse formation of catecholamines that regulate attention, mood, movement, and circadian rhythms
• Iron deficiency during sensitive developmental windows alters neuronal excitability, synaptic pruning, and dopaminergic signalling

The Serotonin-Melatonin Pathway

Serotonin is converted to melatonin (the sleep hormone) in the pineal gland. Since serotonin synthesis requires iron-dependent tryptophan hydroxylase, iron dysregulation can impair melatonin production and disrupt sleep-wake cycles.

Sleep Disruption in ADHD and Autism

ADHD as a Circadian Disorder

Van der Heijden KB et al. "ADHD 24/7: Circadian clock genes, chronotherapy and sleep/wake cycle insufficiencies in ADHD." J Atten Disord. 2018. PMID: 30234417

• Circadian rhythm dysfunction is a clinically significant and highly prevalent phenotype in ADHD
• Delayed sleep phase is common in ADHD
• Associations between ADHD and clock gene variants (CLOCK, PER2, BMAL1)

Coogan AN et al. "ADHD as a circadian rhythm disorder: evidence and implications for chronotherapy." Front Psychiatry. 2025;16:1697900. PMC12728042

• Comprehensive review establishing ADHD-circadian dysfunction link
• Proposes chronotherapy as adjunctive treatment

Iron, Sleep Movements, and Neurodevelopment

Dosman CF et al. "Evaluation of periodic limb movements in sleep and iron status in children with autism." Clin Pediatr. 2015. PMC4610130

• Higher than expected rates of periodic limb movements in sleep (PLMS) in children with ASD
• Both low serum iron levels and higher sleep disorder rates reported in ASD
• Iron supplementation improved sleep quality in 29% of 24 ASD participants with low ferritin

Cortese S et al. "Restless legs syndrome and ADHD." Sleep Med Rev. 2023. DOI: 10.1016/j.smrv.2023.101746

• 44% of children with ADHD may have restless legs syndrome (RLS) vs ~1% of general child population
• RLS is linked to brain iron deficiency, particularly in the substantia nigra
• Iron supplementation improved RLS symptoms in ADHD cohorts

DelRosso LM et al. "Restless sleep disorder and the role of iron in other sleep-related movement disorders and ADHD." Sleep Med Clin. 2022;7(3):18

• Iron acts as a regulator of dopamine signalling in the brain
• Iron deficiency decreases dopamine receptor density and transporter in the striatum
• Altered dopaminergic signalling is integral to both RLS and ADHD

The Overload Paradox for Sleep

Most sleep-iron research focuses on deficiency. But for HFE carriers with iron overload:

1. Brain iron distribution may be uneven — some regions iron-replete, others functionally depleted
2. Oxidative stress from excess iron could damage dopaminergic neurons in the substantia nigra, paradoxically creating functional dopamine/iron deficiency in that region
3. Neuroinflammation from iron overload disrupts sleep architecture independently
4. IRP1/IRP2 oscillations may be dysregulated by constitutively elevated iron, flattening the normal diurnal iron cycling
5. Melatonin synthesis could be impaired if tryptophan hydroxylase function is altered by iron dysregulation

Clinical Implications

1. Sleep quality assessment (polysomnography, actigraphy) is important for ADHD/autism patients with iron dysregulation
2. PLMS screening should be considered, especially given the RLS-ADHD-iron triad
3. Melatonin supplementation may partly compensate for impaired endogenous production
4. Meal timing may affect IRP oscillations — regular feeding rhythms could support iron metabolism regulation
5. Chronotherapy (timed light exposure, fixed sleep/wake times) addresses the circadian component

Cross-References

• Iron-Dopamine-ADHD Axis
• HFE Variants and Brain Iron
• Iron and GABAergic Function
• Elvanse and Mineral Metabolism
• Fatigue and Burnout
• Health Research MOC