The only logical reason for winter and longer pois that comes in my mind, is TO LESS OF VIT D !!
vit is 'made' by the body itself. Needs sun or much daylight , in winter all people getting less vit D. vit D deficiency is related to prostata issues [cancer] and allergies. Google yourself, ok?
ask your doctor for a vitamin d test read my pois history in 'that familiar feel' for the minimal and maximum international standards of the results