Validation of a screening tool for identification of subjects at risk for suboptimal vitamin D status. Developed questionnaire-based screening tool will be used on subjects with various risks for vitamin D deficiency, and compared with 25-OH-vitamin D levels.

Inclusion Criteria:

• Signed Informed consent form (ICF),
• Age between 18 and 65 years at the time of the signature of Informed consent form (ICF),
• Did not change use of vitamin D conatining drugs/supplements for last 6 weeks
• Willingness to follow all study procedures

Exclusion Criteria:

• Pregnancy or breastfeeding,
• Change in use of food supplements containing Vitamin D in last 6 weeks
• Acute ilness
• Mental incapacity that precludes adequate understanding or cooperation.

Adult users and non-users of vitamin D drugs and food supplements living in Slovenia. Participants invited from the database at Nutrition Institute.

Not decided yet