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The vitamin B6 paradox: Supplementation with high concentrations of pyridoxine leads to decreased vitamin B6 function.(2017-10)Vitamin B6 is a water-soluble vitamin that functions as a coenzyme in many reactions involved in amino acid, carbohydrates and lipid metabolism. Since 2014, >50 cases of sensory neuronal pain due to vitamin B6 supplementation were reported. Up to now, the mechanism of this toxicity is enigmatic and the contribution of the various B6 vitamers to this toxicity is largely unknown. In the present study, the neurotoxicity of the different forms of vitamin B6 is tested on SHSY5Y and CaCo-2 cells. Cells were exposed to pyridoxine, pyridoxamine, pyridoxal, pyridoxal-5-phosphate or pyridoxamine-5-phosphate for 24h, after which cell viability was measured using the MTT assay. The expression of Bax and caspase-8 was tested after the 24h exposure. The effect of the vitamers on two pyridoxal-5-phosphate dependent enzymes was also tested. Pyridoxine induced cell death in a concentration-dependent way in SHSY5Y cells. The other vitamers did not affect cell viability. Pyridoxine significantly increased the expression of Bax and caspase-8. Moreover, both pyridoxal-5-phosphate dependent enzymes were inhibited by pyridoxine. In conclusion, the present study indicates that the neuropathy observed after taking a relatively high dose of vitamin B6 supplements is due to pyridoxine. The inactive form pyridoxine competitively inhibits the active pyridoxal-5'-phosphate. Consequently, symptoms of vitamin B6 supplementation are similar to those of vitamin B6 deficiency.
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Veilige maximale dagdosering vitamine D in voedingssupplementen : aanvullende berekening bij een hogere vitaminering van smeerbare vetten(Rijksinstituut voor Volksgezondheid en Milieu RIVM, 2015-01-19)Vitamin D is important for strong bones and teeth. When exposed to sunlight the skin is able to produce vitamin D itself. In addition, diet is a source of vitamin D. Some foods naturally contain vitamin D; however this vitamin is also added to foods, like spreadable fats. Persons at risk of low vitamin D status are recommended to take vitamin D supplements. These are young children, women 50 years onward, men 70 years onward, persons with dark colored skin, pregnant women and persons with inadequate exposure to sunlight. Besides taking supplements, it is also possible to increase the vitamin D intake by consumption of foods fortified with vitamin D. The maximum daily dosage vitamin D in supplements should then be adapted. The RIVM calculated the effect of increment of the vitamin D level in spreadable fats, like margarine, on the safe maximum daily dosage vitamin D from supplements. The vitamin D intake of the Dutch population will substantially increase in this scenario. The safe maximum daily dosage vitamin D from supplements will slightly decrease. This calculation is an addition on research published in 2013. Both researches are conducted commissioned by the Dutch ministry of Health, Welfare and Sports. The results will help this ministry in their consideration revising the legal maximum vitamin D levels in supplements and/or fortified foods. For several years there is a maximum daily dosage for vitamin D in supplements and for the amounts of vitamin D added to foods. These maxima are set to prevent too high intakes that are associated with too high calcium levels in blood or urine, which may result in kidney stones. The maximum levels are determined based on the 'tolerable upper intake level'. The European Food Safety Authority (EFSA) revised the tolerable upper intake level for vitamin D in 2012. For persons from 1 year onward the tolerable upper intake level has been increased.
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Vitamine A voorziening van de Nederlandse bevolking(2004-12-20)In this report vitamin A intake is assessed. From these analyses, 17 to 30 per cent of the adults in our study were found to have an inadequate vitamin A intake to maintain sufficient vitamin A stores. A substantial proportion of these individuals had a level of intake greatly less than required. Our data were taken from the third Dutch National Food Consumption Survey (1997/98) and we applied a method proposed in a previous study (Waijers et al., 2004), taking into account within- and between-individual variation in intakes and requirements. The term vitamin A refers to retinoids and provitamin A carotenoids, with vitamin A intake expressed in retinol equivalents. Because retinol equivalent ratios used in the Netherlands are dated, we estimated retinol (activity) equivalents for all products in the Dutch food composition table from 2001. Next, we estimated the usual vitamin A intake from the observed intakes. We also estimated average vitamin A requirements, adapting a formula from the American Institute of Medicine, using characteristics of the Dutch population. The probability approach was then applied to estimate the proportion of individuals with an intake under their requirement, combining the usual intake and the requirement distribution. Considering the inadequate vitamin A supply to a considerable proportion of the Dutch population we recommend sound monitoring of developments in the vitamin A intake and investigation of the health consequence of the current low vitamin A supply.
