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Vitamin D deficiency: a clearer picture!
10/14/15

It is worth remembering that the same team, headed by Axelle Hoge, a PhD student at the Department of Public Health of the University of Liege, used the NESCaV study as a basis to establish that 44.7% of the population in Wallonia were vitamin D deficient.  This finding did not surprise the researchers given the lack of sunlight in our country during long periods of the year and the low consumption of food products rich in vitamin D.

“A vitamin is a substance that can be found in food and which is vital for our biological processes. For example, we need vitamin C for the hydroxylation of collagen; a deficiency of this vitamin causes scurvy…Vitamin D is a bit particular because, in contrast with other vitamins, our bodies can produce it. So vitamin D3 is either contained in food or it is synthesised from cholesterol, which is vital due particularly to its involvement in cell membranes. Cholesterol is transformed by biochemical reactions in the skin, the liver and the kidneys to produce active vitamin D3”, explains Professor Philippe Kolh, a lecturer in biochemistry and human physiology at the University of Liege and co-author of this study. The precursor to vitamin D3 therefore passes through the skin which is affected by ultraviolet light rays. “Because there is less light in winter and therefore weaker ultraviolet rays, vitamin D synthesis is very limited. Cutaneous exposure of entire limbs (face and hands is not sufficient) for at least thirty minutes per day is required in order to produce sufficient amounts of vitamin D without factoring in dietary intake”.

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What is vitamin D used for?

Vitamin D is used for calcium absorption in the intestine. “Because it is fat-soluble, it can enter the cells, attach itself to the DNA of the cell in question and stimulate the synthesis of proteins. In the case of a lack of vitamin D, intestinal absorption of calcium will be insufficient and this can be problematic, particularly in individuals whose needs are greater, such as women who are breast-feeding, children or those who are suffering from diseases that require bone regeneration…” continues Professor Kolh. Calcium is necessary for homeostasis. “If the organism is lacking in calcium, because it has not been absorbed in sufficient quantity in the intestine due to vitamin D deficiency, then the body will take calcium from wherever it can. Because calcaemia is mainly controlled by the parathyroid, the latter will release parathormone which acts on the bones drawing on their reserves of calcium and phosphate; in addition, this will have an effect on the kidneys to avoid leakage of calcium in urine while at the same time increasing renal excretion of phosphate. This is why vitamin D deficiency can be detected by means of a blood sample, because, even if the level of calcium is normal following its extraction from bone, a high level of parathormone indicates that the process to counteract vitamin D deficiency is under way”.

Who is vitamin D deficient?

There are still very few epidemiological studies available on the proportion of the population that is vitamin D deficient in Belgium. But Axelle Hoge’s team (she is the first author of the study) conducted the investigation in our country: nearly one in two individuals are vitamin D deficient. “It is estimated that there is a vitamin D deficiency when the serous concentrations of 25-hydroxyvitamin D (25(OH) D) are less than 50 nmol/litre; nonetheless, concentrations of between 50 and 75 nmol/litre are still considered to be insufficient. The figures show that greater deficits have been recorded in men (56% as against 45.1% in women, when they do not take vitamin D supplements; 29.1% as against 21.4% respectively when they take supplements). It has also been observed that individuals who use sunbeds are less deficient: 38.4% as against 55.7% of individuals who do not use sunbeds and do not take supplements; but the ratio is still 27% as against 8.4% in those who do take supplements. Those who are exposed to sunlight are also slightly less affected giving a rate of deficiency of 60% to 49%; but this group remains large even if they take supplements, around 20%. Finally and interestingly, it was observed that the BMI of the individuals studied is involved: 45.7% of individuals of normal weight who do not take supplements suffer from vitamin D deficiency (the number for those who do take supplements is around17%); the number for individuals who are overweight is 52.7% (22% with vitamin D supplement); obese individuals make up around 63.3% (and a relatively high number of 45% despite taking supplements!)”. To clarify these figures, the study shows that the incidence of vitamin D deficiency is very high in winter: 62.1%, against 29.6% in summer.

 

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