Insufficient intake of vitamin D is a public health problem, affecting about 40% of the Finnish population in the winter. Vitamin D has a wide range of health effects: in addition to its effect on bone, it is known to affect inflammatory response among other things. The sources of vitamin D are the synthesis in the skin as well as diet and dietary supplements. In Finland and in Northern Europe vitamin D is formed in the skin only from March to October. This alone is not sufficient to cover the need for year-round, because vitamin D storage is used in a few months. During the winter months the only sources of vitamin D are diet and vitamin preparations. Current vitamin D recommendations are usually based on studies in white population. However, there can be a difference in the need of vitamin D and in vitamin D metabolism between different population groups. More research evidence is needed from the northern countries. The aim of this study is to evaluate the vitamin D need in Somali immigrant population and in original Finnish population. The hypothesis is that the Somalis need more vitamin D to exceed the serum 25(OH)D concentration of 50 nmol/L than the original Finnish population.

Inclusion Criteria:

• woman between 21-66 years of age
• belongs to original Finnish population or to Somali immigrant population
• healthy (= no disease requiring medication)
• lives in the metropolitan area

Exclusion Criteria:

• pregnant or breastfeeding
• has traveled to a sunny destination or destination near the equator during the previous month
• plans to travel to a sunny destination or destination near the equator in the next 6 months
• has used a tanning bed during the previous month
• plans to use a tanning bed in the next 6 months
• the subject's blood 25-hydroxy-vitamin D level (25 (OH) D), exceeds 100 nmol / L or is less than 30 nmol / L at baseline in the screening phase.