Madam

The Institute of Medicine's (IOM) latest recommendations⁽¹⁾ defining the formal RDA of vitamin D required for good health (15 μg vitamin D for persons aged 1–70 years and 20 μg vitamin D for persons aged >70 years) are largely inconsequential, because the change from the 1997 IOM recommendations (5–15 μg/d, depending on age)⁽²⁾ is so small. Also the IOM committee ignored the consensus of hundreds of vitamin D research scientists and nutritionists from at least twenty-five countries who attended the 13th Vitamin D Workshop in 2006 in Victoria, British Columbia, Canada⁽Reference Norman, Bouillon and Whiting³⁾ and the14th Workshop in 2009 in Brugge, Belgium⁽Reference Henry, Bouillon and Norman⁴⁾. For a definition of one unit see footnote 1.

There are two major components of the consensus of these scientists. First, research over the past decade has resulted in the addition of four physiological systems to vitamin D's responsibilities, acting through the steroid hormone 1α,25-(OH)₂vitamin D, for good health maintenance and disease prevention, including: (i) the immune system (both innate and adaptive); (ii) the cardiovascular system; (iii) muscle; and (iv) the pancreas and metabolic homeostasis⁽Reference Norman and Bouillon⁵⁾. Second, it is generally agreed that in North America and Western Europe half of the elderly population is vitamin D-deficient; in the rest of the world, about two-thirds of the total population does not receive adequate amounts of the vitamin to even maintain healthy bone⁽Reference Norman, Bouillon and Whiting³⁾.

Both governmental agencies worldwide and individuals are now at a nutritional crossroads with respect to choosing their appropriate vitamin D intake. There are two choices. Both governments and individuals can accept the very conservative advice of the IOM focused on bone health and forgo the benefits to good health that could accrue with a higher daily intake of vitamin D. Or we can, acting as individuals, become informed about and make our own decisions regarding our personal daily intake of vitamin D. When I am asked for my advice, I suggest (in congruence with many vitamin D scientists), a vitamin D intake of 50–100 μg/d for adults. This is stated to be a ‘tolerable dose’ e.g. safe by the current IOM report. Research strongly suggests that a lifetime vitamin D intake at this safe level would prevent borderline vitamin D deficiency, reduce many diseases, increase the longevity and quality of life, and diminish medical care costs worldwide⁽Reference Norman and Bouillon⁵⁾.

How can people acquire this dose? Under the right circumstances exposure to sunlight can generate significant amounts of the vitamin, but this method has two drawbacks. First, sunlight exposure can result in skin cancer as well as non-lethal skin damage⁽Reference Gilchrest⁶⁾. Second, approximately one-third of the world's citizens (2·3 billion) live between 40°N and 90°N where, for a significant portion of the year, the amount and intensity of sunshine is inadequate.

Is it better to provide proper vitamin D supplements or to fortify food with vitamin D? Unfortified foods with useful amounts of vitamin D are rare, the best sources being animal products such as fatty fish and liver extracts (cod-liver oil). In the USA, the Food and Drug Administration has approved the fortification of milk and milk products, breakfast cereal, orange juice, pastas, infant formulas and margarines. In third-world countries reliable sources of vitamin D-enriched food are often entirely lacking. Thus, inexpensive forms of vitamin D supplementation need to be made available in the correct dosage range.

The failsafe remedy for concerned citizens, therefore, is personal vitamin D supplementation. Inexpensive capsules are available for adults to achieve an intake of 50–100 μg/d. Both the 1998 and 2010 IOM committees and many other concerned scientists believe that an individual's vitamin D nutritional status should be determined by carrying out serum assays for 25-hydroxyvitamin D [25(OH)D]. Table 1 provides a sequential series of six guidelines concerning serum 25(OH)D levels as a measure of relative vitamin D nutritional status: (i) severe vitamin D deficiency; (ii) vitamin D deficiency; (iii) vitamin D insufficiency; (iv) marginal vitamin D status; (v) vitamin D sufficiency; and (vi) risk for toxicity. The serum 25(OH)D levels that define the first three categories are also endorsed by the 2010 IOM committee. The author and many other scientists in the field believe that the range of 20–30 ng/ml is a state of marginal vitamin D status and that, to ensure an adequate response by the calcium homeostatic system as well as the four new biological systems, it is essential to have achieved a state of ‘vitamin D sufficiency’; this is a serum 25(OH)D concentration in the range of 30–60 ng/ml (75–150 nmol/l).

Table 1 Serum 25-hydroxyvitamin D (25(OH)D) levels define a person's vitamin D status (modified from Norman and Bouillon⁽Reference Norman and Bouillon⁵⁾)

Thus an annual physical examination should include a determination of the blood level of 25(OH)D, which should fall in the range of 30–60 ng/ml; see Table 1. Maintained consistently, such a vitamin D blood level will ensure good bone health and, at the same time, help realize the vitamin's wide range of new-found benefits.