This paper is the first to take an in-depth look at the adequacy of current dietary, supplementation, and food fortification practices of countries worldwide to provide needed intakes of vitamin D. Until just recently, it was thought that most individuals synthesized all their vitamin D needs with routine exposure of their face and arms to sunlight and therefore very little attention was given to determining the adequacy of dietary vitamin D intake.

“Health scientists are becoming increasingly aware of the importance of vitamin D to prevent a variety of chronic diseases, but there is a current dilemma facing the public as to what the appropriate source of vitamin D should be.”

Three major findings in the last decade have forced us to take a closer look at the adequacy of vitamin D intake. First, an epidemic of rickets or severe vitamin D deficiency in breast-fed dark-skinned infants prompted us to look at the vitamin D status of the entire population, which led to the discovery of a surprisingly high prevalence of poor vitamin D status in North America, especially in dark-skinned individuals and the elderly.

Second, a growing number of cross-sectional observational studies report significant association between low circulating 25-hydroxyvitamin D, the main indicator of vitamin D status, and increased risk of osteoporosis, diabetes, cancer, and autoimmune disorders, causing us to conclude that there is potential for serious health risks associated with poor intake or impaired photosynthesis of vitamin D.

The third important finding is that the previous circulating levels of 25-hydroxyvitamin D that were thought to be adequate or sufficient in otherwise healthy individuals are now widely recognized to be deficient/insufficient and are associated with increased risk of serious chronic diseases. It is now very clear, that North Americans in general are becoming more reliant on dietary sources to maintain adequate circulating levels of 25-hydroxyvitamin D.

Many individuals avoid sun exposure for various reasons, including fear of increased risk of skin cancer, or for cultural or religious reasons they wear clothing that blocks vitamin D synthesis. Those North Americans living at latitudes above 37° N cannot synthesize vitamin D in the winter months when sunlight does not have sufficient UVB rays that are required for vitamin D synthesis. And homebound individuals, or the elderly and darkly-pigmented individuals, cannot synthesize sufficient vitamin D in the summer. Without sufficient dietary vitamin D in these situations, individuals are placed at greater health risk due to vitamin D insufficiency.

Our review reveals the general global inadequacy of the food supply to provide adequate vitamin D intake in countries without mandatory fortification of important staple foods such as milk or margarine. Those clinicians advocating total avoidance of sunlight to reduce the risk of skin cancer need to know that increased reliance on the food supply for sources of vitamin D will necessitate public health strategies that provide greater availability of fortified food staples, dietary supplement use, and/or changes in dietary patterns to increase the intake of vitamin D-rich foods, such as fish.

Health scientists are becoming increasingly aware of the importance of vitamin D to prevent a variety of chronic diseases, but there is a current dilemma facing the public as to what the appropriate source of vitamin D should be.

Casual skin exposure to sunlight which stimulates vitamin D synthesis in the skin was previously thought to be the major source of vitamin D. However, safety concerns about sun exposure have resulted in guidelines that clearly limit sun exposure to prevent skin cancer.

Dietary sources of vitamin D are suggested as suitable alternatives to the lost source of vitamin D when sun exposure is limited, but this recommendation was made without establishing the ability of the food supply to meet these needs.

We examined the current estimates of vitamin D intake world-wide and show evidence that the current food supply, pattern of use of dietary supplements, and dietary patterns of most countries, do not provide enough vitamin D to meet the dietary intake guidelines or individual needs.

Drs. Calvo and Whiting initially focused on reporting the prevalence of vitamin D insufficiency in their respective North American countries, the US and Canada. Each country faces a unique problem concerning vitamin D status of the population, and yet they share common dietary guidelines.

Vitamin D insufficiency in Canada is largely associated with its northerly location and insufficient source of sunlight to synthesize vitamin D over a significant number of months in a year, even in its predominantly light-skinned population.

In the US where the population is more heterogeneous, there is a greater prevalence of vitamin D insufficiency among the darker-skinned individuals living at all latitudes, but notably in the northern latitudes year round.

Our research provides valuable information that can help government agencies formulate public health strategies that will allow them to effectively improve the nutritional quality of their unique food supply. It contributes to our overall goal of achieving better health through optimal nutrition.