## 2 Materials and Methods  
### Questionnaire  
To assess vitamin D knowledge, attitudes, and behaviors, a validated questionnaire identified in the literature was used [17]. The questionnaire was translated into Danish and further piloted with five female students who had a non-Western ethnic minority background. During the pilot, three items (Nr 8: \"Currently, vitamin D deficiency is one of the most important health issues in our country\"; Nr 17: \"Urbanization prevents sun exposure and production of required vitamin D\"; and 21: \"The undesirable taste of sea foods for Iranians is one of the barriers to their consumption of dietary sources of vitamin D\") were considered specific to Iranian background and omitted from the Danish version of the questionnaire. Due to the specifics of the scale scoring system (i.e., recalculating the final scores into 0-100 points), the exclusion of separate items from the scale was possible. The final questionnaire consisted of 10 items for vitamin D general knowledge, 5 items for vitamin D nutrition knowledge, 10 items for vitamin D attitudes, and 10 items for vitamin D behaviors. Vitamin D general and nutrition knowledge questions/items had the response options \"Yes\", \"No\", and \"Don't Know\", which, depending on the item, gave 2, 0, or 1 points; the points were summed into \"general knowledge\" and \"nutrition knowledge\" scales. The vitamin D attitudes and behaviors' questions/items had five-point Likert scale responses ranging from \"strongly disagree\" to \"strongly agree\" for the attitudes; from \"never\" to \"always\" for the behaviors' questions; and, depending on the question, giving 1 to 5 points, which were summed into \"attitudes\" and \"behaviors\" scales. All of the above scales were transformed into 0-100-point scores. The higher the score, the better the vitamin D knowledge, attitudes, or behaviors. The difference between the attitudes' and behaviors' concepts was that the attitude questions concerned knowledge about the behaviors needed to maintain optimal vitamin D levels (e.g., Nr. 19 \"Full time indoor occupation prevents the sun exposure required for production of vitamin D\") while the behavior questions concerned individual's actual behavior (e.g., Nr. 36 \"During the day I am directly exposed to sunlight outdoors\").  
To categorize ethnic background, the respondents were asked which ethnicity they identify themselves as: Danish, Western immigrants or descendants, or non-Western immigrants or descendants. Such ethnic background categorization is used by Statistics Denmark based on the information which country a person and her/his parents are born in or immigrated from. In our questionnaire, the respondents were asked to both identify their ethnic category themselves and write down the country they and both of their parents were born in. Statistics Denmark has developed the country grouping \"western / non-western countries\" and has used it since 2002. According to this grouping, \"non-western countries\" include Turkey and countries outside Europe except the United States, Canada, Japan, Australia, and New Zealand [18].  
Finally, the respondents were asked about gender, age, the highest completed education, employment status, and the use of headwear (yes/no). The questionnaire was inputted into the SurveyXact (Ramboll) online survey system. The electronic version of the questionnaire was tested with the staff of one of the community pharmacies to assess feasibility of the questionnaire's outline and time needed to answer all the questions.