EDITORIAL

 

Inadequate levels of D: not a D-elicious perspective

Niveles inadecuados de D: no es una D-eliciosa perspectiva

 

 

Quesada Gómez J.M., Navarro Valverde C.

Unidad de Metabolismo Mineral - Servicio de Endocrinología y Nutrición - Hospital Universitario Reina Sofía de Córdoba - Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC) - RETICEF - Córdoba

Correspondence

 

 

In the last few decades clinical research in large population studies has revealed the high prevalence of insufficient levels of vitamin D across the globe [1], which, combined with its effects on bone, the muscular-skeletal system, innate and acquired immunity, the cardiovascular system, and the development and function of cells, makes this a first order problem in public health. In fact, low levels of vitamin D are associated significantly with all the causes of morbimortality [2].

The description in this number of the Review of Osteoporosis and Mineral Metabolism of inadequate levels of vitamin D in patients with spinal injury in Las Palmas de Gran Canaria, a city in Spain which, due to its climate, is a paradigm for the ease of obtaining vitamin D₃ by cutaneous synthesis throughout the year, again challenges us [3]. Due to its high prevalence, its ease of detection, its associated adverse consequences, and its simple, cheap and efficacious means of treatment, vitamin D insufficiency should be an urgent and immediate priority for health services in general and for every medic, irrespective of their specialism.

Blood levels of 25 hydroxyvitamin D are considered to be a marker for the status of vitamin D in the body, including endogenous synthesis from to exposure to the sun, dietary ingestion of foods with or without supplements or drug treatments [4].

However, blood levels of 25 hydroxyvitamin D are not strictly regulated, no method for their quantification is perfect, with a great variability between laboratories, even the most properly checked, which, therefore, makes the definition of normality difficult [5]. In fact those methods which do not use high pressure separation chromatography do not distinguish between the metabolites of vitamin D₂ or vitamin D₃ [6]. Although in Spain this is not a problem since vitamin D₂ is not used in normal clinical practice, many metabolites of vitamin D are quantified as 25 hydroxyvitamin D, 24,25 dihydroxyvitamin D₃, its epimer C-3, or sulphated forms, etc., and this problem persists even when using high pressure liquid chromatography separation and mass measurement [7].

Nevertheless, while they need to improve substantially, the methods available in our normal practice of treatment or research are adequate enough and should be used more in our clinical practice for the diagnosis and follow up of treatment.

So, in the face of the variability of the different laboratories and different testing methods, the controversy regarding cut off points for normal blood levels of 25 hydroxyvitamin D proposed by different scientific societies, above 20 ng/ml for the Institute of Medicine [3] and above 30 ng/ml for the International Osteoporosis Foundation (IOF) [8], supported by the recommendation of the Endocrinology Society in the US [9], is a byzantine argument, and only one way of approaching the problem.

In any case, we could agree that the objective should be to achieve blood levels higher than 20 ng/ml as a bare minimum, and preferably higher than 30 ng/ml. So, if our patients have levels of 25 hydroxyvitamin D above 30 ng/ml we will be in agreement with existing recommendations.

Blood levels higher than 30 ng/ml will foster proper bone health and an effective response to antiresorptive treatments for osteoporosis [10,11], in addition to its more than likely beneficial impact on practically all the body's organs and systems [2,12].

Defining the maximum values is more critical. Although for some time it has been proposed that high values of vitamin D, except above toxic values, would not be damaging, there is currently an open debate as to whether high levels of 25 hydroxyvitamin D may be associated with risk of cardiovascular death, or death by other causes [13]. Therefore, some authors have proposed a recommended cut off point blood levels of 25 hydroxyvitamin D of 60 to 70 ng/ml quantified by the usual measurement methods, which are values present in the Summer in agricultural workers, fishermen, lifeguards at the beach or swimming pool etc., who have a high exposure to ultraviolet rays and an intense epidermic production of vitamin D3, but who never exhibit toxicity [3].

In the treatment of vitamin D insufficiency/deficiency, after the optimisation of 25 hydroxyvitamin D levels within the range of 30 to 70 ng/ml, we should not forget its maintenance once this range is reached.

To achieve this objective, in Spain we may use vitamin D₃ or 25 hydroxyvitamin D₃ (calcifediol), which means that we must remember that contra to what we have come to believe for many years, these metabolites are not equipotent, but that the latter is approximately three times more powerful than the former [14,15].

Finally, we would like to stress that, regarding the already recognised high prevalence in Spain of insufficient levels of vitamin D in all sections of the population studied [16,17], which is always greatest in patients with conventional risk factors for having low blood levels of vitamin D, the increase in obesity and poverty [18] will presumably make the current critical situation worse in the coming years.

Unfortunately, current public health policies do not auger well for effective change in the face of this serious problem, which is why we must end our comments with a quote from Robert Heaney, ending one of his interventions at the VI Symposium of SEIOMM held in Granada in October 1997 on the problem of vitamin D deficiency: "....we have the evidence; but when will we see the action.".

 

 

Correspondence:
José Manuel Quesada Gómez
Servicio de Endocrinología y Nutrición
IMIBIC
Hopital Universitario Reina Sofía
Avda. Menendez Pidal, s/n
14004 Córdoba (España)
Correo electrónico: jmquesada@uco.es

 

 

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