radiocompetitive dosage of 25 hydroxyvitamin d and 24 25dihydroxyvitamin d in geriatrics study of seasonal variations dosages of 25 oh d and of 24 25 oh 2 d in the plasma were done in march and october in 26 women more than 70 years old hospitalized in a semichronic disease hospital of the paris area eleven young adults studied in june served as control there was a significant decrease of 25 oh d and 2425 oh 2 d in older individuals pl 0001 in march the levels of 25 oh d and 2425 oh 2 d were respectively 27 16 mgml and 088 053 mgml in october the level of 25 oh d 58 26 mgml were significantly higher p l 001 whereas the level of 2425 oh 2 d did not vary 084 058 mgml these results are in agreement with those obtained in england the underline the relative deficit vitamin d in older individuals the constant decrease of 24 25 oh 2 d remained unexplained