Determinants of vitamin D status in a general population of Danish adults.

BACKGROUND AND AIMS: Danish legislation regarding food fortification has been very restrictive and vitamin D deficiency is thought to be common in Denmark due to inadequate dietary intakes and the fact that in Denmark (latitude 56°N) vitamin D is only synthesized in the skin after exposure to solar radiation during summertime (April-September). The purpose of this study was to evaluate the vitamin D status of a general adult population in Denmark and, in addition, associations between vitamin D status and distinct lifestyle factors were studied.

METHODS

A random sample of 6784 persons from a general population aged 30-60 years participated in a health examination in 1999-2001. Serum samples from all participants were stored and levels of 25-hydroxyvitamin D (25(OH)D) were measured by HPLC in 2009. The method was compared to another HPLC method. Information on dietary intake of vitamin D and other lifestyle factors were obtained by questionnaires. A total of 6146 persons defined as ethnic Danes and with successful measurements of 25(OH)D were included in the analyses.

RESULTS

The overall prevalence of vitamin D deficiency (25(OH)D<25 nmol/l) and insufficiency (25(OH)D<50 nmol/l) were 13.8% and 52.2%, respectively. A marked seasonal fluctuation was seen in serum levels of 25(OH)D - median values of 25(OH)D were lowest in February and highest in August. In multiple logistic regression models (n=5506), low vitamin D status was significantly associated with obesity (BMI≥30), daily smoking and a sedentary lifestyle. However, measurements of 25(OH)D were not associated with the estimated dietary intake of vitamin D. Comparison of two HPLC methods demonstrated considerable differences in accuracy.

DISCUSSION AND

CONCLUSIONS

Our results suggest that poor vitamin D status is common among adults in a Northern European country without food fortification with vitamin D. Methodological issues are, however, of great importance when using cut-off values to define poor vitamin D status. In addition, we demonstrated that low serum levels of 25(OH)D were associated with several lifestyle factors.