Challenges in Achieving Adequate Vitamin D Status in the Adult Population/ Part 2

Inclusion Criteria: * vitamin D suboptimal status * Signed Informed consent form (ICF), * Caucasian race * Age between 18 and 65 years at the time of the signature of Informed consent form (ICF), * Willingness to avoid a consumption of any food supplements containing Vitamin D during the study, except the ones prescribed by the study researchers, and to avoid use of solarium or other artificial UVB sources * Willingness to follow all study procedures Exclusion Criteria: * Pregnancy or breastfeeding, * Known or suspected allergy to any ingredient of the tested products in Part 2, * Pronounced avoidance of sunshine (eg reporting of allergy to the sun) * Use of food supplements containing Vitamin D or fish oil or omega 3 fatty acids in last three months prior to inclusion, * Special dietary habits used by a small part of the population (veganism, low-carb high-fat (LCHF) diet, caloric restriction diet, note: vegetarians are not excluded) * Diets prescribed by the medical profession * Disorders of the kidneys, thyroid, digestive tract, osteoporosis and other bone diseases, skin diseases * Other diseases and conditions that affect the absorption and synthesis of vitamin D * Exposure to stronger sunlight in the last three months prior to engaging in a survey (travel to countries with stronger sunshine, use of solarium), * The consumption of margarine or plant substitutes for milk / milk products several times a day, as these foods are most often enriched with vitamin D, * Visiting the solarium in the last three months before joining the survey, * Mental incapacity that precludes adequate understanding or cooperation.