There is growing evidence that vitamin D levels are associated with a protection from a number of diseases. In particular diseases that centre on the development of insulin resistance such as the metabolic syndrome, type 2 diabetes, obesity and cardiovascular disease, as well as cancer. Vitamin D is synthesised in the skin via the action of ultraviolet light from the sun, and this is the best way to obtain the vitamin. Foods do contain vitamin D, and possibly its active metabolite 25-hydroxyvitamin D, but the levels are thought to be insufficient to produce the blood concentrations that are protective of disease. The current trend of reduced sun exposure due to erroneous concerns over the safety of the sun’s light explains the chronic low levels of vitamin D measured in many group of the population. Those In institutions, children and the elderly are particularly prone to vitamin D deficiency due to limited sun exposure. Fortification of foods is one proposed solution to this problem, and some countries have adopted this strategy.
That vitamin D fortification of food could be an effective way to increase the vitamin D intakes of a given population has been demonstrated in those countries that currently fortify certain foods. For example, in one study1, the vitamin D levels of two groups of individuals was compared at baseline and following intervention with vitamin D fortified foods. In the vitamin D fortified individuals, the prevalence of vitamin D deficiency decreased from 67 to 57 % following 10 years of treatment, and the median intake of vitamin D also increase in both supplement and non-supplement users, although the increase was small. Therefore fortified foods show the potential to increase the vitamin D intakes of free living populations exposed to vitamin D fortified foods. However, the increase was small and clearly the number of individuals with vitamin D deficiencies was still large even after 10 years of exposure to fortified foods. A number of countries currently fortify milk, including Canada and the United States.
Plants need the sun to produce energy. Animals need the sun to produce vitamin D. The ultraviolet rays from sunlight are by far the best way to obtain vitamin D, as many thousands of IU can be produced in just a short time in direct sunlight. However, in higher latitudes in the winter, it is not possible to always obtain enough vitamin D from the sun. Supplements are therefore recommended throughout the winter months.
Therefore evidence suggests that fortification of foods with vitamin D does have a potential impact on vitamin D status, but that the effects are small. Further many have vitamin D deficiencies that are so severe that the small amount of vitamin D added to foods does not benefit them. Therefore the best way to increase vitamin D levels remains frequent sun exposure, which can produce tens of thousands of IU of vitamin D in a short amount of time. However, many individuals do not have access to the sun for large periods of the year. Therefore for these individuals, vitamin D supplements remain the most cost effective and efficient way of improving vitamin D status. Evidence shows that high intakes of supplemental vitamin D in tablet or capsule is effective at not only maintaining summer levels, but also increasing blood levels further, raising the blood concentration to the optimal range for disease protection. However, when sun exposure is possible in the summer, supplements are not needed.
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