I must have read it in this book:
The Origins of the British: A Genetic Detective Story

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I’ve traced my direct genealogy through numerous royal bloodlines, roman emperors and byzantine rulers.
Among Europeans, the Irish seem to have the highest rate of O+. The luck of the Irish?
Iceland is just behind Ireland--if you count together both O+ and O- they are tied. Icelanders have a lot of Celtic DNA (from ancestors enslaved by the Norse).
I have read that too.