There is an epidemic of lack of vitamin D in Europe;  less than 5% of the population reaches the ideal level of 40-50 ng/ml in their blood stream, while the majority has a level somewhere between 5 and 20 ng/ml.
The diffuse lack of vitamin D is a factor that accelerates the processes of physical and mental aging, including cognitive decadence.  Of interest is the news from Boston University, published in 
Dermato-Endocrinology, according to which mushrooms left in the sun for 60 minutes before cooking and eating are rich in vitamin D and become a natural integrator of this vitamin.