This week, Professor Luke dives into a condition that affects Ireland more than almost anywhere else on Earth: haemochromatosis, the iron-overload disorder sometimes dubbed “the Celtic disease”. And we owe this one to two listeners, Kayden and Kari, who emailed Luke asking him to shine a light on it. 

Here’s the remarkable thing: 1 in 83 Irish people have haemochromatosis. Globally, it’s closer to 1 in 10,000. Why are we so unusually affected? Luke explores the Founder Effect, seen in remote and island populations, where one ancient genetic mutation spreads widely over generations. Some researchers even wonder if it goes back to a single ancestor in early medieval Ireland… perhaps as far as Niall of the Nine Hostages in the 4th century. 

The science is striking. Haemochromatosis is caused by mutations in the HFE gene, which tell the body to absorb far too much iron from food. Instead of being flushed out, the excess iron lodges in tissue and organs, and in severe cases can damage the liver, pancreas, heart and joints. Luke explains why the iron in our blood reddens when exposed to oxygen — essentially a biological version of rust — and how that same chemistry becomes dangerous when iron builds up inside the body. 

Symptoms often creep in slowly: persistent fatigue, joint pain (especially in the hands), abdominal discomfort, and in more advanced cases, sallow or bronzed skin, an enlarged liver, and a higher risk of diabetes. People with haemochromatosis are also more vulnerable to infections such as listeria and hepatitis because iron can fuel bacterial growth — something pathogens love. 

Treatment, however, is wonderfully simple and astonishingly old-school: you remove blood. Phlebotomy — supervised blood withdrawal — lowers iron levels safely and effectively. Women often experience milder symptoms before menopause because regular blood loss naturally curbs iron accumulation. There are also medications that help reduce iron levels when needed, and lifestyle tweaks matter too: avoid iron supplements, and keep alcohol intake modest, because alcohol increases iron storage. 

Luke also explores a fascinating evolutionary angle: in times of famine or scarcity, people genetically predisposed to absorb more iron may have been better equipped to survive. That survival advantage could explain why the mutation became so common in Ireland and neighbouring regions — another classic Founder Effect story. 

It’s a condition that’s easy to diagnose, highly treatable, and crucial to catch early — and now, thanks to Kayden and Kari, you’ll understand the science behind it. 

Email Luke anytime with your own ideas for future episodes at laoneill@tcd.ie — your question might inspire the next podcast.