Research shows that vitamin D may play a role in lowering the risk of certain types of cancer, cardiovascular disease, type 2 diabetes, immune and infectious disorders, physical performance and some autoimmune diseases. But how much vitamin D does a person really need for optimal health?
The Institute of Medicine's (IOM) Food and Nutrition Board believes that vitamin D studies during the past 10 to 15 years present conflicting and mixed results. Although leading vitamin D researchers recommend vitamin D supplement levels of 2,000 international units (IU) or 4,000 IU or even 10,000 IU in particular situations of demonstrated deficiency the IOM believes that recommending such high levels is unwarranted. The vitamin D researchers, however, are quick to point out that the majority of the IOM members do not have experience with vitamin D research.
The IOM's newly released recommended dietary allowance (RDA) for vitamin D suggests 600 IU for people age 70 and under, and 800 IU for those over age 70. This is a slight increase beyond the previous RDA (200 IU for children and younger adults, 500 IU for adults age 50-70 and 600 IU for older adults).
However, the IOM claims that the majority of Americans and Canadians are getting enough vitamin D. Yet, some medical practitioners believe that many individuals are deficient. Research at McGill University Health Centre in Canada suggests that 59 percent of people are deficient in vitamin D and 25 percent are severely deficient.
D. Lee Alekel, professor and osteoporosis and vitamin D researcher at Iowa State University, offered this perspective on the differing claims.
The difference of opinion stems from various criteria for what constitutes vitamin D deficiency based on serum concentrations. For example, while vitamin D researchers would classify an individual as vitamin D deficient, the IOM would classify that same person as at risk of deficiency. Likewise, researchers may classify someone as having inadequate levels of vitamin D, while the IOM would classify that same person as at risk for inadequacy.
There also is controversy about the upper limit established by the IOM. The panel increased the upper limit for vitamin D supplements from 2,000 to 4,000 IU, noting concerns about the safety of higher levels. But many vitamin D researchers believe the IOM's upper limit, as well as the RDA, is too low.
Matthew Rowling, assistant professor and vitamin D researcher at Iowa State noted, "We do not have good evidence that daily vitamin D intakes in adults between 4,000 and 10,000 IU are toxic. However, recommending daily intakes above 4,000 IU for the general public is not a sensible approach, unless this is physician-prescribed for a particular condition or due to frank deficiency."
In addition, the IOM suggested the recommended dietary allowance could be achieved through dietary intake alone and supplements were not needed; however, Registered Dietitians disagree.
To consume 600 IU from milk, the primary source of vitamin D for many, would require drinking six cups daily. Although other foods like orange juice, some cheeses, yogurts, margarines and breakfast cereals are fortified with vitamin D, excessive amounts would be needed - for example, 15 servings of fortified cereal - to meet the recommendations.
What is a person to do? The Iowa State University specialists suggest the following steps.
Engage in outdoor activity whenever possible and let the sun work its magic. Just 20 minutes of direct sunlight (prior to applying sunscreen) will stimulate adequate vitamin D production in individuals under age 70. At peak summer sunlight (10 a.m. to 2 p.m.), exposure of the face and hands to the sun for 15 to 20 minutes produces 10,000 IU of vitamin D.
Consume foods fortified with vitamin D including milk, margarine, cheese and orange juice. Naturally occurring sources of vitamin D include fatty fish, such as tuna, salmon and mackerel, as well as egg yolks and beef liver.
Consider a vitamin D supplement if living in northern climates and dietary intake of foods listed above is not consistent. Many experts recommend 1,000 IU/day during the summer and fall with marginal sunlight exposure and 2,000 IU/day during the winter and spring.