Writing in the prestigious New England Journal of Medicine (NEJM), IOM vitamin D committee members note that only evidence for vitamin D’s bone health benefits was “sound […] for determining the population's needs”.
Such evidence led to the IOM to increase the recommended dietary allowances (RDAs) of vitamin D to 600 IU per day for persons 1 to 70 years of age.
“The committee concluded that vitamin D plays an important role in bone health and that the evidence provides a sound basis for determining the population's needs,” wrote JoAnn Manson, MD, DrPH, from Harvard Medical School, Susan Mayne, PhD, from Yale Schools of Public Health and Medicine, and Steven Clinton, MD, PhD, from Ohio State University.
“For outcomes beyond bone health, however, including cancer, cardiovascular disease, diabetes, and autoimmune disorders, the evidence was found to be inconsistent and inconclusive as to causality,” they added.
Drs Manson, Mayne, and Clinton also state that the prevalence of vitamin D inadequacy in the US is overestimated, and that 97.5 percent of the population has adequate levels (defined as 25-hydroxyvitamin D concentrations above 20 ng/mL for bone health).
A step in the right direction, but…
While the need for an increase was welcomed by all, the degree of the increase was not, with a number of high profile vitamin D researchers speaking out that the new recommendations did not go far enough, with some calling for 1000 IU.
In response to the NEJM article, Michael Holick, PhD, MD, Professor of Medicine at Boston University Medical Center and a world-renowned expert in vitamin D, told NutraIngredients-USA.com: “If you believe the current recommendations, you will be vitamin D insufficient.”
Indeed, Dr Holick noted that he was part of the 1997 IOM committee for vitamin D recommendations, which led to a RDA of 200 IU. “If you believed the recommendations then, you would have been vitamin D deficient,” he said.
Vit D and the Big C
The link between vitamin D intake and protection from cancer dates from the 1940s when Frank Apperly reported in Cancer Research a link between latitude and deaths from cancer, and suggested that sunlight gave "a relative cancer immunity".
Since then a raft of studies has floated down the science river reporting risk reductions for a range of cancers, including colorectal, breast, oral, stomach, and pancreatic.
According to Dr Holick, the association between high vitamin D levels and lower incidences of cancer continues, and he can see “no other explanation” than vitamin D reducing the incidence.
Dr Holick also criticized the NEJM statement about a scarcity of randomized-trial evidence for vitamin D. For example, Drs Manson, Mayne, and Clinton wrote: “In the WHI trial, calcium plus vitamin D3 did not reduce the incidence of colorectal cancer or related mortality.”
Such a statement does not tell the whole story, said Dr Holick, who himself wrote in NEJM in 2007 (Vol. 357, pp. 266-281): “Participants in the Women's Health Initiative who at baseline had a 25-hydroxyvitamin D concentration of less than 12 ng per milliliter (30 nmol per liter) had a 253 percent increase in the risk of colorectal cancer over a follow-up period of 8 years.”
There is definite biological plausibility, added the Boston-based researchers, with vitamin D able to regulate cell growth, cause a cell to die if it becomes malignant, or by shutting down blood supply if malignancy does occur.
“The bottom line is that there is no downside to increasing vitamin D,” he said.
Illuminating the facts about Vit D
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
Source: New England Journal of Medicine
Published online ahead of print, doi: 10.1056/NEJMp1102022
“Vitamin D and Prevention of Cancer — Ready for Prime Time?”
Authors: J.E. Manson, S.T. Mayne, S.K. Clinton