Madam

Important decisions are now being made by the public health community regarding applications of vitamin D for reducing the incidence of breast and colon cancer, type 1 diabetes, multiple sclerosis, bone fractures and other conditions caused mainly, in whole or part, by vitamin D deficiency.

Consensus on public health measures and methods of disease prevention is normally based on evaluation of the totality, consistency and reproducibly of available epidemiological evidence across study designs and throughout populations around the world. Evidence for effective prevention is not necessarily limited to results of randomized controlled trials (RCT), and few public health decisions in medical history have been based on them.

Science is built on observation and inference. By making an egregious decision to exclude most or all evidence from epidemiological observational studies, the authors of the recent US Institute of Medicine (IOM) monograph on vitamin D and calcium requirements⁽¹⁾ failed to provide readers with the benefit of a vast panoply of proof that has been acquired using observational studies. Inexplicably, a new RCT that used an aetiologically relevant dose of vitamin D₃ (1100 IU/d or 27·5 μg/d) and Ca (1450 mg/day)⁽Reference Lappe, Travers-Gustafson and Davies²⁾ also was excluded by the IOM. That RCT documented substantial prevention of all types of cancer combined in volunteers assigned to vitamin D and Ca.

The epidemiological evidence that vitamin D and Ca are able to prevent a substantial proportion of several important and common types of invasive cancer is consistent and compelling⁽Reference Garland, Gorham and Mohr³⁾. It includes approximately twenty-five major cohort studies of vitamin D intake, an equal number of nested case–control studies of serum 25-hydroxyvitamin D (25(OH)D) concentrations, a score of modern ecological studies, and the above new RCT.

Observational studies are subject to testing with well-defined and time-tested criteria for causation, the Hill criteria⁽Reference Lilienfeld and Stolley⁴⁾. These criteria include strength of association, presence of a dose–response gradient, reasonable consistency among studies, temporal sequence and coherence with biological knowledge⁽Reference Garland, Gorham and Mohr³⁾. These criteria have been used to establish the cause of many diseases of public health importance, including all diseases related to use of cigarettes or other tobacco, and all occupationally or environmentally caused diseases.

There is a distinguished history of using observational studies to determine aetiology in public health. To his undying credit, Dr John Snow, the founder of modern epidemiology, used only observational studies. He did not randomly allocate the inhabitants of London's Broad Street to drink or not drink contaminated water. Instead he used ecological mapping studies, cohort studies and case–control studies to reach and confirm his compelling observation that cholera is transmitted mainly by drinking contaminated water.

One hundred and fifty years after Snow's landmark observations, the public health community is at a moment in medical history where it cannot ethically conduct an experiment withholding vitamin D from persons who are in need of it to avoid several serious diseases. Vitamin D, with its many preventive benefits, can no longer be ignored by the public health community. The nearly universal deficiency that exists in most developed countries must be eradicated. Sufficiency should logically be restored to the physiological levels of the outdoor-dwelling equatorial ancestors of modern humanity, in the range from 60–80 ng/ml (150–200 nmol/l). Fortunately this can be achieved using new IOM guidelines without waiting years for another RCT.

The ‘no observed adverse effect level’ (NOAEL) recently recognized by the US IOM is 10 000 IU (250 μg)/d⁽¹⁾. Now is the time for the public health community to act upon this important statement from the IOM and begin large-scale field trials of vitamin D for prevention of chronic diseases. Such field trials could to include whole communities, states or countries. Dosages should be in the range of 4000–10 000 IU (100–250 μg)/d. Serum 25(OH)D ideally should be measured routinely when possible, with the goal of establishing a range of 60–80 ng/ml (150–200 nmol/l).

The vitamin D revolution will occur without performance of additional RCT, as most great public health measures have. Major sound and reasonable public health measures have been widely adopted without trials. These include smoking prohibitions and warnings, use of seat belts and motorcycle helmets, and posting of speed limits along roadways.

Society is speeding along a dangerous course of vitamin D and Ca deficiency. The public health risks are visible around us as breast and colon cancers, multiple sclerosis, type 1 diabetes, some forms of IHD and other diseases now known to be due in whole or part to vitamin D deficiency.

Based on the new IOM guidelines, it is now not only unnecessary to allow vitamin D deficiency to continue unchecked at such high prevalence, needlessly predisposing the population to many serious chronic diseases – it is morally unjustifiable.