Vitamin D, the ongoing discussion
Much has been written and said about vitamin D in Portugal in recent years. The media attention surrounding this topic stems from a set of circumstances that involve not only the recognition of its importance in human health but also the realization that a significant portion of our population may not have adequate levels of this vitamin.
It is therefore important to take stock of the matter, especially since we often witness statements that do not correspond to the truth at all and may even be more harmful than helpful.
Situation of the Portuguese population
Therefore, and firstly, we will describe the situation of the Portuguese population with regard to plasma vitamin D levels.
There is no study that assesses the entire Portuguese population using a representative sample, so the available data only refers to some specific subpopulations, namely the elderly, children, and individuals with certain pathologies. Therefore, they should be interpreted with due caution.
In a representative sample of 1500 elderly Portuguese people, the Nutrition UP65 study found that a very significant proportion of them, around 40%, exhibit levels of Deficiency, while 30% have Insufficiency, always using the most widely accepted criteria, those of the Institute of Medicine, United States of America.
In a sample of adolescents from the Porto region ( https://doi.org/10.1017/S1368980017002804 ), low levels of this vitamin were also observed, with a particular incidence in the winter months.
In another sample of adult patients with Metabolic Syndrome, approximately 38% also had levels of Deficiency ( https://doi.org/10.1186/s12902-017-0221-3 ).
Although there are some doubts about the accuracy of the values obtained, given that they were not obtained using the reference method (which is liquid chromatography with tandem mass spectrometry detection, LC-MS), they point to a situation of globally low levels that are likely to cause health damage, especially at the osteoarticular level.
The confidence with which we state this is due to the fact that, although these values were obtained by another analytical methodology (electrochemiluminescence), an important study by Cashman and colleagues shows that there is a good correlation between the methods and that any overestimation or underestimation by electrochemiluminescence is not of sufficient magnitude to, given the large number of individuals with low levels, cease to concern us in this regard ( https://doi.org/10.3945/ajcn.115.120873 ).
Therefore, it is important to understand what factors may be at the origin of this situation, and we must first consider the sources of vitamin D, namely ultraviolet B (UVB) solar radiation, diet, and dietary supplements.
Sources of Vitamin D: UVB rays
UVB levels in a country like Portugal are generally sufficient (UV Index above 3) during the spring and summer, but insufficient for the skin to synthesize this vitamin during the autumn and winter months.
Thus, this important source is only available during part of the year, and the use of sunscreen practically eliminates its cutaneous synthesis in any season. If we add to this individuals with few hours outdoors, those who cover a large part of their body with clothing, individuals with darker skin, and the elderly (in these two groups the ability to synthesize vitamin D is diminished), we have the conditions for low levels of cutaneous synthesis of this vitamin.
Vitamin D in the diet
Diet also presents problems as a source of vitamin D. Data from the 2015-2016 National Food Survey show that around 95% of Portuguese people do not consume the recommended amount, a phenomenon that is not surprising given the scarcity of food sources, which are limited to fish and fortified foods, still rare in Portugal.
The measures to be taken to urgently correct this situation will essentially involve widespread supplementation or mandatory food fortification. This is because any recommendations to increase sun exposure are not only impossible for a significant part of the year, but also clash with legitimate concerns about the increased likelihood of skin cancer from exposure to ultraviolet rays.
Certainly, much more will have to be done before a national strategy can be proposed in this regard, but what does not seem reasonable is to maintain the current state and continue to subject populations and health services to the high number of osteoarticular diseases (and possibly others) resulting from such low vitamin D levels.
