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Mouse mitochondria run on AM–PM rhythms rather than 24-hour cycles
This week brought surprising discoveries about how our internal clocks actually work—and what happens when they don't. From mice revealing that metabolism runs on 12-hour rhythms to massive studies linking shift work with heart damage, the science is rewriting what we know about biological time.
🕐 Mouse liver runs on 12-hour cycles, not 24-hour ones
Male mice showed that most liver metabolic functions—especially carbohydrate and fatty acid processing—follow 12-hour rhythms rather than the expected 24-hour circadian cycles
This 12-hour rhythmicity accounts for 25-50% of overall metabolic variability and closely aligns with when nutrients are available throughout the day
Mitochondrial activity also fluctuates on these shorter cycles, suggesting the liver adapts energy production twice daily to match the body's changing demands
Why it matters: This challenges the fundamental assumption that biological clocks are primarily 24-hour systems and suggests our metabolism is more precisely tuned to meal timing than previously understood.
Key Findings
🫀 Shift work directly damages heart tissue in animal studies
Meta-analysis of 32 animal studies found that circadian disruption causes significant cardiac hypertrophy, with left ventricle-to-body weight ratios increased substantially
Both genetic clock gene knockouts and environmental disruption (like light phase shifts) led to pathological heart remodeling and elevated stress markers
The heart damage occurred at both organ and cellular levels, with enlarged heart muscle cells and increased fibrotic markers
🌙 Evening people face 84% higher prostate cancer risk from night shifts
Meta-analysis of shift workers found that those with evening chronotypes had 84% higher prostate cancer risk compared to day workers
Each additional year of night shift work increased prostate cancer risk by 2.1% specifically for evening chronotype workers
Morning chronotype shift workers also showed increased risks for breast cancer and mental health problems, suggesting chronotype matching doesn't protect against shift work harms
🧠 Night shift drivers show early heart damage and gut changes
66 night shift ride-hailing drivers had significantly higher NT-pro-BNP levels (49.8 vs 41.3 pg/ml) compared to 175 day shift drivers—a marker of early heart stress
Night shift workers showed 20 different gut microbiome changes, with 4 bacterial taxa specifically linked to heart injury markers
The gut microbiome alterations correlated with cardiovascular biomarker changes, suggesting a possible gut-heart connection in shift work damage
🧬 Circadian imbalance genes predict diabetes and mood disorders
Genome-wide study of 312,935 people identified 27 genetic loci linked to circadian imbalance, including known clock regulators like CALCA and CRX
People with higher circadian imbalance genetic scores showed increased risks for type 2 diabetes, major depression, and obesity
Genetic analysis suggested that circadian disruption may actually cause diabetes, mood swings, and heart attacks—not just correlate with them
💊 Timing thyroid cancer treatment to evening may boost effectiveness
Thyroid-stimulating hormone (TSH) naturally peaks overnight, but current radioactive iodine therapy protocols ignore this circadian rhythm
Since TSH drives the sodium-iodide symporter that helps thyroid cells absorb radioactive iodine, evening dosing could align with peak TSH levels
The theory suggests evening treatment timing could enhance iodine uptake, improve cancer-killing effects, and reduce whole-body radiation exposure
🐟 Clock genes control antiviral immunity in zebrafish
Zebrafish with mutations in circadian genes cry1a and cry1b showed increased viral loads and reduced survival when infected with Tilapia lake virus
cry1a mutants had lower initial expression of antiviral receptor tlr22, while cry1b mutants showed reduced antiviral gene Mxa expression later in infection
Both mutant lines also showed altered behavior (increased activity) and disrupted gut microbiomes, particularly more Proteobacteria in cry1a mutants
Implications
The evidence is converging: our internal clocks don't just tell time—they actively protect our health through precise metabolic and immune coordination. When these rhythms break down from shift work or genetic variants, the damage appears to be direct and measurable, from heart tissue changes to weakened antiviral defenses.
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