title: [High prevalence of vitamin D deficiency in the south-west Netherlands].
abstract: OBJECTIVE
  To determine how often vitamin D deficiency occurs in the populations of a city, the countryside and urbanised areas of the countryside, and also the influence of the seasons.
  
  
  METHODS
  Cross-sectional study carried out in the winter and summer of 2013. Trend analysis from requests for determination of vitamin D levels by general practitioners between January 2010 and August 2012.
  
  
  METHODS
  In a random sample survey of all blood samples received by SHL-Groep (diagnostic center for primary care) between 21-01-2013 - 10-03-2013 (winter period) and 01-08-2013 - 30-08-2013 (summer period), Vitamin D levels of the residual material were measured. We reported the results by age group, gender and postal code area in the following areas: The Hague (city), Province of Zeeland (countryside) and West Brabant (urbanised countryside). In addition, the average vitamin D concentration obtained from all the requests for determination of vitamin D levels between January 2010 and August 2012 was measured against the time of year.
  
  
  RESULTS
  During the winter period 58.8% of the 2503 participants had a vitamin D serum concentration of < 50 nmol/l (The Hague: 65.6%; Zeeland: 50.9%). A total of 29.9% had vitamin D levels of < 30 nmol/l. In men under the age of 50 years, this was 38.2%. Of the 1910 people tested during the summer, 35.4% had a vitamin D level of < 50 nmol/l (The Hague: 43.7%; Zeeland: 33.5%). 11.6% had a vitamin D level < 30 nmol/l. General practitioners requested the vitamin D levels of 50,441 patients. The average vitamin D level varies considerably with the seasons.
  
  
  CONCLUSIONS
  Vitamin D deficiency occurs frequently, even in relatively young people and more so in cities than in the countryside. The average vitamin D concentration varies with the seasons.
authors.affiliation: SHL-Groep, Etten-Leur.
authors.forename: Leandra J M
authors.initials: LJ
authors.lastname: Boonman-de Winter
authors.forename: Arjan
authors.initials: A
authors.lastname: Albersen
authors.forename: Karin
authors.initials: K
authors.lastname: Mohrmann
authors.forename: Carla M A C
authors.initials: CM
authors.lastname: Bakx-van Baal
authors.forename: Dirk W
authors.initials: DW
authors.lastname: Meijer Timmerman Thijssen
authors.forename: J P H M Hans
authors.initials: JP
authors.lastname: Bressers
mesh_terms: D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D015995:Prevalence; D012621:Seasons; D014807:Vitamin D / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood / Q000453:epidemiology*
chemical_list: D014807:Vitamin D