No association between birth season and vitamin D concentration in adults in a North Norwegian population—the Tromsø study

We found the associations in the article by Lippi et al. ‘Birth season and vitamin D concentration in adulthood’ very interesting (1). We therefore decided to look for the association between birth season and serum 25-hydroxyvitamin D [25(OH)D] levels in a comparable North Norwegian population of 10,203 subjects who participated in the Tromsø study in 2007-2008 (2). Since Tromsø is situated at 69 degrees north, there are significant seasonal variations of daylight with periods of polar night and day.