[High prevalence of vitamin D deficiency in the south-west Netherlands]

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.

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.

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.

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.

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.