Are there any conditions that stop you from absorbing vitamin d? my son spends lots of time outside and not always with sun cream and has supplements equivalent to 3 times recommended day lie amount, but is still defficiant and I am wondering why.
Where do you live so we know the latitude? What color skin does he have? How much does he weigh? Please define the daily amount or total Vitamin D supplement he takes? You would also have to define “a lot of time outdoors” and “not always with sun cream”. All of this can be a factor.
Any kind of stomach or intestinal problems may cause less absorption of the supplement.