I think it’s a dietary deficiency thing. A lot of our food tho processed is heavily fortified with vitamins and minerals. E.g some bread is fortified with omega 3, cereals and grains may be fortified with iron and salt fortified with iodine.I noticed the Phillipines and India got so many people born with birth defects.
Side note: The US govt tested to see how a lack of certain vitamins affected humans by depriving black ppl of certain vitamins and minerals to see what the RDA should be. Maybe it was the UK government can’t remember
Anyway that’s why you don’t see as many wild deformities like that in first world countries