title: Vitamin D deficiency and seasonal and inter-day variation in circulating 25-hydroxyvitamin D and parathyroid hormone levels in indoor daytime workers: a longitudinal study.
abstract: Seasonal variation in circulating 25-hydroxyvitamin D (25OHD) levels related to seasonal and inter-day fluctuation in sunlight ultraviolet irradiation, may lead to misjudgments concerning 25OHD status in individual workers around threshold levels. Here, to examine seasonal and inter-day variations in plasma 25OHD, we conducted a longitudinal study involving indoor daytime workers. Subjects were four male indoor daytime workers aged 32-57 yr working in Kawasaki City, Japan. Blood samples were obtained on six days within two two-week periods in February and October, 2008. Plasma 25OHD, serum intact parathyroid hormone (PTH) and 1α,25-dihydroxyvitamin D [1α,25(OH)(2)D] were measured. Individual monthly mean 25OHD levels were 16-56% higher in October than in February (p=0.03), while individual monthly mean intact PTH levels were 15-41% lower in October (p=0.09). No seasonal change was observed in 1α,25(OH)(2)D (p=0.62). Notably, nearly all measured 25OHD levels in February were lower than the reference value of 20 ng/ml. Our study identified the occurrence of seasonal variation in circulating 25OHD and intact PTH levels, even after accounting for inter-day variability, and hypovitaminosis D in wintertime in indoor daytime male workers in Japan. Due to this variability, single spot measurements of 25OHD may lead to misjudgment of workers' vitamin D status.
authors.affiliation: National Institute of Occupational Safety and Health, 6–21–1 Nagao, Tama-ku, Kawasaki, Japan. itoh-hiroaki@umin.ac.jp
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Itoh
authors.forename: Ippei
authors.initials: I
authors.lastname: Mori
authors.forename: Yuki
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Syou
authors.initials: S
authors.lastname: Maki
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Ogawa
mesh_terms: D000328:Adult; D006801:Humans; D007564:Japan; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D016273:Occupational Exposure; D010281:Parathyroid Hormone / Q000097:blood* / Q000528:radiation effects; D012621:Seasons; D014466:Ultraviolet Rays / Q000009:adverse effects; D014807:Vitamin D / Q000097:blood / Q000528:radiation effects*; D014808:Vitamin D Deficiency / Q000097:blood* / Q000209:etiology; D014940:Work Schedule Tolerance / Q000523:psychology
chemical_list: D010281:Parathyroid Hormone; D014807:Vitamin D