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Alpha-MSH: The Forgotten Sunlight Hormone Behind Fatigue, Weight Gain and Low Mood



Obesity is often framed as a problem of food choices, calorie excess, or personal discipline. But what if the real issue lies upstream - not in what we’re eating, but in the signals our brain is (or isn’t) receiving from the environment?



At the centre of this idea is a neuropeptide called alpha-MSH (alpha melanocyte-stimulating hormone) - acritical player in both pigmentation and energy regulation.



Alpha-MSH is derived from POMC (pro-opiomelanocortin), a precursor molecule that’s activated in response to full-spectrum UV light. 



Once activated, POMC is cleaved into multiple bioactive compounds including alpha-MSH and beta-endorphins. 



These hormones perform wide-ranging functions:



 • In the skin, alpha-MSH stimulates melanocytes, triggering tanning as a protective response to UV exposure.



 • In the brain, particularly the hypothalamus, it plays a key role in appetite regulation, energy expenditure, sexual behaviour, and immune modulation.



In an evolutionarily consistent environment - where humans spent the majority of their time outdoors - this pathway allowed light to calibrate key systems: metabolism, mood, circadian rhythm, and immune tolerance.



But in our modern indoor world, we’ve drastically disrupted this interface. Chronic underexposure to natural light, combined with artificial blue light, circadian mismatch, and inflammatory inputs - leads to a breakdown in this signalling cascade.



The result?



 • Impaired alpha-MSH and melanocortin signalling.



 • Reduced hypothalamic control over appetite and energy balance.



 • A system that defaults to conservation: store fat, suppress output, and seek comfort.



What looks like sluggishness is often a survival response / an adaptive shift in brain body communication under stress.



The melanocortin system also links tightly to leptin, the hormone that signals energy sufficiency. When leptin signalling is impaired, either by inflammation, disrupted light cues, or nutrient imbalance, the brain behaves as though it’s in a famine. Hunger increases, energy drops, and the body becomes metabolically rigid.



Crucially, this isn’t just about weight. Alpha-MSH also modulates the immune system, barrier integrity, and mucosal inflammation - with implications for autoimmunity, allergies, and mast cell disorders.



We talk a lot about cutting carbs, avoiding seed oils, and balancing macros. But restoring the original hormonal inputs like light, rhythm, and environmental coherence is equally critical for true metabolic health.



Until we correct the upstream mismatch, we’ll continue fighting downstream symptoms with limited results.



Lauren Wallis Dyer


BSc Nutritional Biochemistry | MSc Medical Molecular Biology


DipCLN | IFMCA 




 
 
 

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