The Federal RDAs for vitamin D are, "grossly inadequate" for most ordinary people, let alone people with pronounced vitamin D deficiencies, according to a detailed analysis of 3,885 episodes of vitamin D supplementation in over 1,300 individuals.
The Federal guidelines, updated in 2011, advise no more than 600 IUs (15 mcg) for men and women aged 51-70, and 800 IU for those over 70.
That ain't gonna cut it, say Drs. Gurmukh Singh and Aaron Bonham.
Dr. Singh of the Department of Pathology, Truman Medical Center, and Dr. Bonham, of the University of Missouri Medical School, Kansas City, compared pre- and post-treatment serum levels against oral dosages and found that doses in the RDA range seldom result in meaningful rises in blood levels.
"We examined the responses of patients to vitamin D replacement under the usual circumstances of healthcare, and analyzed factors affecting the response to treatment using changes in serum concentrations of 25-OH-vitamin D as the indicator of response."
Missing the Mark
"For the whole population, the average daily dose resulting in any increase in serum 25-OH-vitamin D level was 4,707 IU/day; corresponding values for ambulatory and nursing home patients were 4,229 and 6,103 IU/day, respectively," they report in the current edition of the Journal of the American Board of Family Medicine.
These dose levels are an order of magnitude higher than the current RDAs, which were actually increased from the 400 IU limit the Fed recommended prior to 2011.
"About 5,000 IU is usually needed to correct deficiency, and the maintenance dose should be ≥ 2,000 IU/day," say the authors who note that response to supplementation, as indicated by serum concentrations, is affected by many things besides dose. The key factors are: starting serum concentration, BMI, age, and serum albumin concentrations.
This study included 1,327 individuals (943 women, 384 men) seen at two University of Missouri-affiliated hospitals. The patients had an average age of 56, and a mean BMI of 31.5.
They had a wide range of garden-variety chronic diseases including: overweight/obesity, hypertension, diabetes, hyperlipidemia/dyslipidemia, chronic obstructive airway disease, GERD, chronic renal disease, hypothyroidism, and substance abuse problems. Almost all had multiple diagnoses.
A subset of nursing home patients had multiple chronic diseases including MS, stroke, dementia, debilitating cardiovascular, renal and hepatic insufficiency. Some had serious infections with C. difficile and pneumonia.
Tailored Dosing Calculator
Beyond simply questioning the federal guidelines—which have been hotly disputed since they were published--the main point of this study is that vitamin D supplementation, by necessity, needs to be individualized to be effective.
Rather than relying on arbitrarily defined, overly generalized guidelines like the RDAs, Singh and Bonham propose that clinicians take a more rational approach to vitamin D dosing.
They developed an equation that, they claim, accurately predicts the amount of vitamin D, in IUs, that an individual needs to take in order to affect meaningful changes in their serum concentrations.
The calculation is as follows:
Appropriate Dose = [(8.52 - Desired change in serum 25-hydroxyvitamin D level) + (0.074 × Age) - (0.20 × BMI) + (1.74 × Albumin concentration) - (0.62 × Starting serum 25-hydroxyvitamin D concentration)]/(-0.002).
The authors also developed an equation by which clinicians can predict the expected increase of serum vitamin D for a given oral dose level. It is:
End Serum Concentration = 0.07 (Age) – 0.20 (BMI) + 0.002 (Dose) + 1.75(Serum albumin [g/dL]) + 0.38 (Starting 25-hydroxyvitamin D concentration) + 8.48