Challenges in Achieving Adequate Vitamin D Status in the Adult Population - Part 1

Study Overview
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Brief Summary
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Seasonal variations in vitamin D status will be determined on a cohort of Slovenian adults using longitudinal study design, and association between vitamin D status and different Caucasian phototypes, skin colour and melanin index investigated .

Official Title
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Challenges in Achieving Adequate Vitamin D Status in the Adult Population - Part 1

Conditions
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Vitamin D Serum Levels

Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: 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 hihg-fat 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.

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 65 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Difference between vitamin D serum levels in winter and in summer season will be determined | Vitamin D serum level will be measured once in winter (December - January) and once in summer season (August-September) for each individual. The study will be performed over two consecutive years. | 2 years | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Correlation of vitamin D serum levels with Fitzpatrick skin phototype | Fitzpatrick skin phototype will be determined using Fitzpatrick self-evaluation questionnaire in combination with expert assessment in August-September. | 2 years | 
| Correlation of vitamin D serum levels with skin colour measured in CIE Lab colour space | Skin colour will be measured in CIE Lab colour space on inner and outer side of the upper arm. The measurement will be performed in August-September. | 2 years | 
| Correlation of vitamin D serum levels with melanin index | Melanin index will be measured on inner and outer side of the upper arm. The measurement will be performed in August-September. | 2 years |