The results, published in an online issue of the European Journal of Clinical Nutrition (doi:10.1038/sj.ejcn.1602001), show that 74 per cent of the 1379 adults investigated had a mean daily intake of vitamin D lower than 5 micrograms (200IU).
Another study, published in an advance online issue of the journal today (doi:10.1038/sj.ejcn.1602033), reveals that a significant number of immigrant populations in Norway are also seriously deficient in the vitamin. These included both men and women born in Turkey, Sri Lanka, Iran, Pakistan and Vietnam who were residing in Oslo during the study period.
Exposure to sunlight is the greatest source of vitamin D but in north European climates, people are not exposed to enough sun to make adequate levels of the vitamin, argue researchers. A number of scientists have raised the profile of vitamin D deficiency in recent months, demonstrating an association with cancers, autoimmune diseases as well as fractures.
But while sun cancer campaigners refuse to advocate further sun exposure, fortification and supplements are currently the best option for increasing intake of the vitamin.
The new studies confirm that nutritional supplements make a significant contribution to vitamin D intake. In the Irish study, the total mean daily intake from all sources was 4.2 ug when supplements were included but only 3.2ug when only food sources were measured.
Supplements contributed 6.8 and 12 per cent to the average daily intake in men and women, respectively. But overall men had significantly higher intakes than women. This could be due to their food choices.
Meat and meat products contributed more than 30 per cent of the vitamin D intake while fish and eggs provided lower doses. In the Norwegian study, reported use of fatty fish and cod liver oil supplements showed a strong positive association with vitamin D intake in all groups.
A US cancer prevention expert has also called for action to raise vitamin D levels, calling on the government in a recent paper to require calcium and vitamin D to be added to foods. He argues this could achieve a 20 per cent reduction in colon cancer deaths and osteoporosis-related fractures.