People living at Northern latitudes are at risk of suffering from vitamin D insufficiency due to low sun exposure and the risk may be even more pronounced among elite swimmers since indoor training further reduces sun exposure. In light of this, the investigators want to examine vitamin D status in young elite swimmers and if there is an association between vitamin D status and muscle strength.

To examine vitamin D status in young elite swimmers and if there is an association between vitamin D status and muscle strength, twenty-nine swimmers, 12 female and 17 male (16-24 years) residing at latitude 55-56°N were included to the trial conducted in March-April. Blood samples were analysed for serum 25-hydroxyvitamin D (s-25(OH)D) and hand-grip strength was measured as marker of muscle strength. Subjects´ vitamin D and calcium intake were assessed by food frequency questionnaire and sun exposure and training status by questionnaires.

Inclusion Criteria:

Age: 16-35 years

Top atlets, conducting:

• Hard physical activity
• Indoor elitesport min. 10 hours a week
• Healthy, without use of any medications
• Eat fish max 2 times per week

Exclusion Criteria:

• Use of corticosteroids
• Illness
• Use of supplements
• Use of solarium
• Donation of blood within the last 3 months
• Having spent time below the latitude of 42° north from September through April