Fish and shellfish are good sources of vitamin D, and even egg, chicken and meat contain some vitamin D. Vitamin D can also be synthesised in the skin, but this requires sunlight which is lacking during the winter months in the high latitudes. If the skin is covered by clothes, or for persons with dark skin, synthesising vitamin D from the sun becomes inefficient. Vitamin D deficiency is known to be associated with muscle weakness, fatigue and depression in both non-cachectic and cachectic persons (patients having involuntary weight loss due to an underlying disease that cannot be altered by food alone), which is why supplementation is recommended in this group of patients.
The Nordic Nutrition Recommendations state that the population in the Nordic countries need to consume more vitamin D from food to maintain an adequate level of vitamin D in the blood during the whole year. Consequently, some foods are enriched with vitamin D. Despite this, The Nordic Nutrition Recommendations suggest additional use of vitamin D supplementation to infants, pregnant and elderly people.
The recommended intake in the Nordic countries is 10µg for children and adults, and 20 µg for people over 75 years of age. In Europe the recommended intake is 10µg (EFSA guidelines), while the American recommendations are as high as 15 µg for children and adults, and 20 µg for people over 71 years of age. The Smartfish Recharge series of products for healthy individuals and athletes contain 3 to 5 µg vitamin D per 200 ml.