Van alles m.b.t. Vitamine D

[Martijn]

http://www.voedingscentrum.nl/nl/eten-gezondheid/voedingstoffen/vitamines-en-mineralen/vitamine-d.aspx

Ik heb (nog) niet al die linken bekeken, maar neem nou die van het voedingscentrum, op die pagina staat:

Wat gebeurt er al je er te veel van binnenkrijgt?
Bij overmatig gebruik van supplementen kunnen op tal van plaatsen in het lichaam kalkafzettingen ontstaan. Veel zonlicht kan niet leiden tot een overschot aan deze vitamine. Als bovengrens voor een aanvaardbare (veilige) inneming wordt 50 microgram per dag aangehouden, voor kinderen tot één jaar is dat 25 microgram per dag.

1. die grens van 50 microgram per dag kennen we, en die is dus discutabel.
2. er staat "Veel zonlicht kan niet leiden tot een overschot aan deze vitamine", terwijl het lichaam zelf ongeveer maximaal 250 microgram per dag aan vitamine D kan aanmaken. Dus waarom wordt dan een bovengrens voor een aanvaardbare (veilige) inneming van 50 microgram per dag aangehouden?
3. bij welke inname op tal van plaatsen in het lichaam kalkafzettingen kunnen ontstaan, wordt niet aangegeven. Misschien pas bij langdurige veel hogere inname dan 250 microgram per dag.

[arnaud]

Yep, enige nuance lijkt op z'n plek, helaas kan op mijn vraag zelfs artsen geen antwoord geven? ik dacht dat vitaminehuishouding wel kant en klare stof zou zijn..

[bamboe]

Hoi Arnaud,

reguliere artsen leren nagenoeg alleen over medicijnen, niet of nauwelijks over supplementen, tijdens hun opleiding.

groetjes,
Dorien

[vonneke]

http://www.medicalnewstoday.com/articles/191487.php

Genome-Wide Study Identifies Factors That May Affect Vitamin D Levels

An international research consortium has identified four common gene variants that are associated with blood levels of vitamin D and with an increased risk of vitamin D deficiency. The report from the SUNLIGHT consortium - involving investigators from six countries - will appear in The Lancet and is receiving early online release.

"We identified four common variants that contributed to the risk for vitamin D deficiency," says Thomas Wang, MD, of the Massachusetts General Hospital (MGH) Heart Center, a co-corresponding author of the Lancet report. "Individuals inheriting several of these risk-associated variants had more than twice the risk of vitamin D deficiency as was seen in those without these variants."

Vitamin D's essential role in musculoskeletal health is well known, and in recent years epidemiologic evidence has suggested that vitamin D deficiency may contribute to conditions like diabetes, cardiovascular disease and some cancers. Naturally produced in the skin in response to sunlight, Vitamin D has been added to many types of food and is available in dietary supplements. But studies have shown that from one third to one half of healthy adults in developed countries have low levels of vitamin D. While reduced sun exposure is clearly associated with lower vitamin D levels, environmental and cultural factors - including dietary intake - cannot completely account for variations in vitamin levels. The fact that vitamin D status tends to cluster in families suggests a genetic contribution.

The SUNLIGHT (Study of Underlying Genetic Determinants of Vitamin D and Highly Related Traits) Consortium involved a research team from the U.S., U.K., Canada, Netherlands, Sweden and Finland who pooled data from 15 epidemiologic studies of almost 32,000 white individuals of European descent. Results of the comprehensive genetic screening were correlated with participants' serum vitamin D levels. Statistically significant associations were found for four common variants, all in genes coding enzymes involved with the synthesis, breakdown or transport of vitamin D. The risk association was independent of geographic or other environmental factors; and the more variants an individual inherited, the greater the risk of vitamin D deficiency.

"It's possible that these results could explain why some people respond well to vitamin D supplements and others don't, but that needs to be studied further since we didn't specifically examine response to supplementation," Wang explains. "We also need to investigate how genetic background can modify response to sunlight, whether these associations are seen in other populations, and if these gene variants have an impact in the chronic diseases that appear to be associated with vitamin D deficiency."

[vonneke]

What Is Vitamin D Deficiency? Mixed Messages About Sun Exposure :

http://www.medicalnewstoday.com/articles/191407.php

[vonneke]

Osteoporos Int. 2010 Jun 17. [Epub ahead of print]

Are commonly recommended dosages for vitamin D supplementation too low? Vitamin D status and effects of supplementation on serum 25-hydroxyvitamin D levels-an observational study during clinical practice conditions.
Leidig-Bruckner G, Roth HJ, Bruckner T, Lorenz A, Raue F, Frank-Raue K.

Gemeinschaftspraxis für Endokrinologie, Nuklearmedizin und Humangenetik, Brückenstr. 21, 69120, Heidelberg, Germany, thomas.bruckner@t-online.de.

Abstract
Vitamin D deficiency is associated with increased fracture risk. The observational study aimed to investigate vitamin D status and supplementation in ambulatory patients. Only 20% of patients had optimal serum 25-hydroxyvitamin D [25(OH)D] levels. Commonly recommended dosages were insufficient to achieve clinically relevant increase of 25(OH)D levels. Higher dosages were safe and effective under clinical practice conditions. INTRODUCTION: Vitamin D deficiency is associated with adverse health outcome. The study aimed to investigate vitamin D status and supplementation in ambulatory patients. METHODS: Nine hundred seventy-five women and 188 men were evaluated for bone status from January 2008 to August 2008 within an observational study; 104 patients (n = 70 osteoporosis) received follow-up after 3 months. Dosage of vitamin D supplementation was documented and serum 25(OH)D and parathyroid hormone (PTH) determined. RESULTS: In all patients (age, 60.4 +/- 14.1 years), distribution of 25(OH)D was 56.3 +/- 22.3 nmol/L (normal range, 52-182 nmol/L) and PTH 53.8 +/- 67.5 ng/L (normal range, 11-43 ng/L). The proportion of patients with 25(OH)D < 25, 25 to <50, 50 to <75, >/=75 nmol/L was 7.5%, 33.3%, 38.9% and 20.2% in the total group and 20.1%, 38.5%, 30.8%, 10.6% at baseline in the follow-up group, respectively. After 3 months, 3.9% had still 25(OH)D < 25 nmol/L; only 12.5% achieved 25(OH)D >/= 75 nmol/L. In osteoporosis patients, 25(OH)D increased more in those taking >/=1,500 (median, 3,000) IU vitamin D per day (33.1 +/- 14.7 nmol/L) compared with </=1,000 (median, 800) IU/day (10.6 +/- 20.0 nmol/L) (p < 0.0008). PTH decreased more in patients taking >/=1,500 IU/day (-13.2 +/- 15.2 ng/L) compared with </=1,000 IU/day (-7.6 +/- 19.2 ng/L; p = 0.29). 25(OH)D was negatively correlated to PTH (r = -0.49, p < 0.0001). An increase of 25(OH)D >/= 75 nmol/L resulted in normalised PTH. CONCLUSION: Supplementation with higher vitamin D dosages (2,000-3,000 IU/day) is required to achieve a relevant increase of 25(OH)D and normalisation of PTH.

PMID: 20556359

[vonneke]

Hautarzt. 2010 Jun;61(6):478, 480-6.

[The significance of vitamin D metabolism in human skin. An update]

[Article in German]

Trémezaygues L, Reichrath J.

Klinik für Dermatologie, Venerologie und Allergologie, Hautklinik und Poliklinik, Universitätsklinikum des Saarlandes, 66421, Homburg/Saar, Germany. lea-louisa.tremezaygues@uks.eu

Abstract
Vitamin D deficiency is endemic, affecting worldwide approximately more than 1 billion people and approximately 60% of the German population. In recent years, our understanding of the important role of vitamin D for human health has grown enormously. Epidemiological and in vitro investigations as well as animal studies have convincingly demonstrated new important functions of vitamin D, including potent immunoregulatory and growth regulatory properties. We know today that vitamin D deficiency/insufficiency is not exclusively associated with an increased risk for bone diseases, but with a multitude of other diseases (including various types of cancer, cardiovascular diseases, infectious diseases, and autoimmune diseases). We discuss our present understanding of the importance of the cutaneous vitamin D system.

PMID: 20502851

http://www.springerlink.com/content/37531k1761670486/

[vonneke]

http://www.medicalnewstoday.com/articles/192325.php

Predicting An Individual's Vitamin D Needs

Your skin tone and the amount of sunshine you receive--in addition to what foods you eat--can all influence the amount of vitamin D that your body has on hand for optimum health. In a preliminary and apparently first-of-its-kind study, Agricultural Research Service (ARS) research physiologist Charles B. Stephensen and colleagues have developed a preliminary model that predicts an individual's vitamin D requirements.

Stephensen is based at the ARS Western Human Nutrition Research Center at the University of California-Davis.

Scientists have known since the early 20th century that our bodies are stimulated to make vitamin D when ultraviolet rays from the sun reach our skin. But the amount of direct sunlight that a person receives is affected not only by the amount of time spent in the sun, but also by latitude, season, skin pigmentation, and even the amount of protective clothing that one wears.

Some vitamin D comes from food, including salmon and some other fish; milk and breakfast cereals fortified with this essential nutrient, and nutritional supplements such as multivitamin tablets.

The current recommended daily allowance of vitamin D for U.S. adults who are less than 50 years of age is 200 international units.

To develop the preliminary model, Stephensen and co-investigators worked with 72 young adult volunteers who provided intermittent records of what they ate and, for 7- to 8-week stints, wore photosensitive badges from 7 a.m. to 7 p.m. so scientists could determine their level of sun exposure.

Data from the volunteers--either African-American or of European ancestry--who had relatively low amounts of sun exposure suggest that they may need additional vitamin D to reach a target blood level of 75 nanomoles of vitamin D per liter of plasma.

Stephensen cautions, however, that some vitamin D levels indicated by the model exceed the level currently considered safe. More research, with a larger number of volunteers, may refine the predictive power of the model, he reports.

The research was published earlier this year in the Journal of Nutrition.

[vonneke]

Vitamin D Receptor Emerges As A Key Player Amid The Murk Of 'Gut Flora':

http://www.medicalnewstoday.com/articles/194099.php

[vonneke]

Photodermatol Photoimmunol Photomed. 2010 Aug;26(4):172-6.

Is casual exposure to summer sunlight effective at maintaining adequate vitamin D status?

Diffey BL.

Department of Dermatological Sciences, Institute of Cellular Medicine, University of Newcastle, Newcastle Upon Tyne, UK. b.l.diffey@ncl.ac.uk

Abstract

BACKGROUND/PURPOSE: The advice that an adequate vitamin D status can be achieved by short, casual exposure to summer sunlight is ubiquitous. This review will examine the value of this advice.

METHODS: The results of experimental studies on changes in serum 25-hydroxyvitamin D [25(OH)D] concentrations following ultraviolet exposure are interpreted in the context of human exposure to sunlight.

RESULTS: It is shown that current advice about modest sun exposure during the summer months does little in the way of boosting overall 25(OH)D levels, while sufficient sun exposure that could achieve a worthwhile benefit would compromise skin health.

CONCLUSIONS: Failure to understand the nature of human exposure to sunlight has led to misguided advice concerning the sun exposure necessary for an adequate vitamin D status.

PMID: 20626818