Allergic reactions are more common in the north — perhaps because vitamin D levels are lower there:
Carlos Camargo at Harvard School of Public Health and his colleagues estimated the distribution of anaphylaxis in the United States by collecting information from all 50 states about prescriptions of the adrenaline auto-injectors used to treat attacks.Some northern states such as Massachusetts and Connecticut had more than four times more prescriptions of adrenaline, at nearly 12 per 1,000 people, than southern states such as Hawaii and New Mexico, they report in the Journal of Allergy and Clinical Immunology.
“We were very surprised by the large difference, but previous research has shown that a related disease, asthma, follows a latitude gradient too, so the results were not completely unexpected,” says Camargo.