title: Longitudinal changes and seasonal variations in serum 25-hydroxyvitamin D levels in different age groups: results of the Longitudinal Aging Study Amsterdam.
abstract: Vitamin D levels remained fairly stable during ageing with increasing levels in persons aged 55-65 years old and decreasing levels in persons aged 65-88 years old. The seasonal variation was larger than the longitudinal change. Our findings implicate that vitamin D supplementation becomes more important in older age groups and during wintertime.
  
  
  BACKGROUND
  Longitudinal changes in serum 25-hydroxyvitamin D (25-OHD) levels during aging have not been studied extensively. Two studies showed increasing serum 25-OHD levels. One of these studies suggested that there might be decreasing levels in persons aged 65 years and older. The objectives of the current study are the following: (1) to examine longitudinal changes in serum 25-OHD levels in different age groups and (2) to describe the seasonal variation in different age groups.
  
  
  METHODS
  Data of the Longitudinal Aging Study Amsterdam (LASA), an ongoing cohort study, were used. Two different cohorts were included: (1) younger cohort: aged 55-65 years old at baseline, n = 738, follow-up of 6 years and (2) older cohort: aged 65-88 years old at baseline, n = 1,320, follow-up of 13 years.
  
  
  RESULTS
  At baseline, average levels were 56.5 nmol/L in the younger cohort and 51.1 nmol/L in the older cohort. In the younger cohort, a longitudinal increase in the mean serum 25-OHD levels of 4 nmol/L in 6 years was observed; in the older cohort, a longitudinal decrease in the mean serum 25-OHD levels of 4 nmol/L in 13 years was observed. The seasonal variation was ±12 nmol/L in the younger cohort and ±7 nmol/L in the older cohort.
  
  
  CONCLUSIONS
  Long-term serum 25-OHD levels remained fairly stable during aging with slightly increasing levels in persons aged 55-65 years old and slightly decreasing levels in persons aged 65-88 years old. On average, the seasonal variation was larger than the longitudinal change. Our findings implicate that vitamin D supplementation becomes more important in older age groups and during wintertime.
authors.affiliation: Department of Epidemiology and Biostatistics, EMGO Institute for Health and Care Research, VU University Medical Center, Van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands, nm.vanschoor@vumc.nl.
authors.forename: N M
authors.initials: NM
authors.lastname: van Schoor
authors.forename: D L
authors.initials: DL
authors.lastname: Knol
authors.forename: D J H
authors.initials: DJ
authors.lastname: Deeg
authors.forename: F P A M N
authors.initials: FP
authors.lastname: Peters
authors.forename: A C
authors.initials: AC
authors.lastname: Heijboer
authors.forename: P
authors.initials: P
authors.lastname: Lips
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood*; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D012042:Registries; D012621:Seasons; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000453:epidemiology*
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D