The primary aim of the present trial is to study the effect of daily vitamin D supplementation on muscular power and force among non-western immigrants living in Oslo, Norway, and secondarily to study the effect of musculoskeletal pain and headache.

The investigators have also prespecified a number of additional research questions about anemia, metabolism and bone turnover, inflammation, diabetes, lipids, itching and kidney function, which because of multiple comparisons should be interpreted with caution unless the statistical evidence for an effect is very strong.

Vitamin D deficiency is a widespread public health problem among immigrants from non-Western countries in Norway. As a background for preventive strategies it is important to have best possible knowledge about health consequences of poor vitamin D status, and in this respect much is lacking.

The investigators will aim to study the effect of vitamin D supplementation on muscular strength , musculoskeletal pain and headache among non-western immigrants in Norway with background from Middle East, Africa and South Asia. In addition the intervention gives us the opportunity to study the effect of vitamin D on indicators of other important health issues including anemia, diabetes , lipids, inflammation, metabolism and bone health. The study will also contribute with insight on how to achieve a high compliance. This is of interest in a broader context as poor compliance has been experienced as a problem in primary health care among immigrants with poor vitamin D status.

The study is a randomized, double blinded, placebo-controlled trial which compares two doses of vitamin D supplements, 400 IU and 1000 IU, with placebo and the tablets will be taken daily in a period of 4 months. Three muscle strength tests will be used, and they will be performed before and after the intervention: Counter movement jumps, Chair rising and Handgrip. Level and location of musculoskeletal pain and headache will be recorded at baseline and at end of the study.

A blood sample will be collected from the study subjects at baseline and after 4 months. The level of vitamin D and markers of anemia, metabolism and bone turnover, inflammation, diabetes, lipids and kidney function will be measured.

Inclusion Criteria:

• Male and female between 18 - 50 years old
• Immigrants with background from Middle East, Africa and South Asia.

Exclusion Criteria:

• Daily use of vitamin D supplementation and frequently use of artificial UV light exposure.
• Pregnancy
• Malabsorptive disorders
• Fracture in the leg /arm within the preceding 6 months. Known osteoporosis
• Tuberculosis, sarcoidosis, cancer, kidney dysfunction, liver dysfunction and history of kidney stone.
• Regular use of medication that interfere with vitamin D/bone metabolism, such as glucocorticoids, diuretics, lithium, antiepileptics, bisphosphonates,
• Regular use of strong pain killers.
• Medication for diabetes