Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Molecular assessment of muscle health and function : The effect of age, nutrition and physical activity on the human muscle transcriptome and metabolom
    Hangelbroek, Roland W.J. - \ 2017
    Wageningen University. Promotor(en): A.H. Kersten; C.P.G.M. de Groot, co-promotor(en): M.V. Boekschoten. - Wageningen : Wageningen University - ISBN 9789463437103 - 205
    muscles - age - nutrition - physical activity - transcriptomes - metabolomes - elderly - creatine - phosphocreatine - vitamin d - atrophy - spieren - leeftijd - voeding - lichamelijke activiteit - transcriptomen - metabolomen - ouderen - creatine - fosfocreatine - vitamine d - atrofie

    Prolonged lifespan and decreased fertility will lead to an increased proportion of older adults in the world population (population aging). An important strategy to deal with population aging has been to promote healthy aging; not only to prevent mounting health care costs, but also to maintain independence and quality of life of older populations for as long as possible. Close to the opposite of the healthy aging is frailty. A major component of (physical) frailty is sarcopenia: age-related loss of muscle mass. Decreased muscle size and strength has been associated with a wide variety of negative health outcomes, including increased risk of hospitalization, physical disability and even death. Therefore, maintaining muscle size and strength is very important for healthy aging. Nutrition and physical activity are possible strategies to maintain or even improve muscle function with age.

    The effect of nutrition, age, frailty and physical activity on the function of skeletal muscle is complex. A better understanding of the molecular mechanisms involved can provide new insights in potential strategies to maintain muscle function over the life course. This thesis aims to investigate these mechanisms and processes that underlie the effects of age, frailty and physical activity by leveraging the sensitivity and comprehensiveness of transcriptomics and metabolomics.

    Chapter 2 and 3 describe the effects of age, frailty and resistance-type exercise training on the skeletal muscle transcriptome and metabolome. Both the transcriptome and metabolome show significant differences between frail and healthy older adults. These differences are similar to the differneces between healthy young men and healthy older adults, suggesting that frailty presents itself as a more pronounced form of aging, somewhat independent of chronological age. These age and frailty related differences in the transcriptome are partially reversed by resistance-type exercise training, in accordance with the observed improvement in muscle strength. Regression analysis revealed that the protocadherin gamma gene cluster may be important to skeletal muscle function. Protocadherin gamma is involved in axon guidance and may be upregulated due to the denervation-reinnervation cycles observed in skeletal muscle of older individuals. The metabolome suggested that resistance-type exercise training led to a decrease in branched-chain amino acid oxidation, as shown by a decrease in amino acid derived carnitines. Lastly, the blood metabolome showed little agreement with the metabolome in skeletal muscle, indicating that blood is a poor read-out of muscle metabolism.

    We assessed the effect of knee immobilization with creatine supplementation or placebo on the skeletal muscle transcriptome and metabolome in chapter 4. Knee immobilization caused muscle mass loss and strength loss in all participants, with no differences between creatine and placebo groups. Knee immobilization appeared to induce the HDAC4-myogenin axis, which is primarily associated with denervation and motor neuron diseases. The metabolome showed changes consistent with the decreased expression of energy metabolism genes. While acyl-carnitine levels tended to decrease with knee immobilization, one branched-chain amino acid-derived acyl carnitine was increased after knee immobilization, suggesting increased amino acid oxidation.

    Vitamin D deficiency is common among older adults and has been linked to muscle weakness. Vitamin D supplementation has been proposed as a strategy to improve muscle function among older populations. In chapter 5, supplementation with vitamin D (calcifediol, 25(OH)D) is investigated as nutritional strategy to improve muscle function among frail older adults. However, we observed no effect of vitamin D on the muscle transcriptome. These findings indicate the effects of vitamin D supplementation on skeletal muscle may be either absent, weak, or limited to a small subset of muscle cells.

    Transcriptomic changes due to different forms of muscle disuse are compared in chapter 6 (primarily knee immobilization and bed rest). The goal was to determine the similarities and differences among various causes of muscle atrophy in humans (primarily muscle disuse). Both knee immobilization and bed rest led to significant changes in the muscle transcriptome. However, the overlap in significantly changed genes was relatively small. Knee immobilization was characterized by ubiquitin-mediated proteolysis and induction of the HDAC4/Myogenin axis, whereas bed rest revealed increased expression of genes of the immune system and increased expression of lysosomal genes. Knee immobilization showed the highest similarity with age and frailty-related transcriptomic changes. This finding suggests that knee immobilization may be the most suitable form of disuse atrophy to assess the effectiveness of strategies to prevent age-related muscle loss in humans.

    The transcriptome and metabolome are incredibly useful tools in describing the wide array of biological systems within skeletal muscle. These systems can be modulated using physical activity (or lack thereof) as well as nutrition. This thesis describes some of these processes and highlights several unexplored genes and metabolites that may be important for maintaining or even optimizing muscle function. In the future, it may be possible to optimize both exercise and nutrition for each individual using these techniques; or even better, cheaper and less invasive alternatives.

    Vitamin D for older adults : Determinants of status, supplementation strategies and its role in muscle function
    Vaes, Anouk M.M. - \ 2017
    Wageningen University. Promotor(en): C.P.G.M. de Groot, co-promotor(en): M. Tieland. - Wageningen : Wageningen University - ISBN 9789463436144 - 164
    vitamin d - deficiency - aging - vitamin supplements - dosage effects - musculoskeletal system - literature reviews - food enrichment - skeletal muscle - food supplements - randomized controlled trials - vitamine d - deficiëntie - verouderen - vitaminetoevoegingen - doseringseffecten - skeletspierstelsel - literatuuroverzichten - voedselverrijking - skeletspier - voedselsupplementen - gestuurd experiment met verloting

    Vitamin D has been identified as an important factor in healthy aging and is receiving growing attention in clinical research. Vitamin D is a fat-soluble molecule, which is synthesized by hepatic and renal or extra-renal hydroxylation into the active hormone 1,25-dihydroxyvitamin D (1,25(OH)2D). The main function of this metabolite is to regulate calcium and phosphorus homeostasis and to support bone mineralization. In the circulation, the 25-hydroxyvitamin D metabolite (25(OH)D) is most stable and thus, considered the best marker of vitamin D status. A serum 25(OH)D concentration <30-50 nmol/L is considered deficient. Given the increased risk of deficiency and the potential beneficial effect of supplementation on musculoskeletal health, older adults present a specific target group for vitamin D interventions. However, the optimal serum 25(OH)D concentration is a matter of ongoing debate as randomized trials show conflicting results.

    With the research presented in this thesis, we aimed to gain insight in the prevalence and main determinants of a low vitamin D status, to investigate strategies to prevent or reverse vitamin D deficiency, and to study the effect of vitamin D supplementation on muscle strength and physical performance in Dutch older adults.

    In chapter 2, we examined the prevalence and the main determinants of a low vitamin D status in a large population of community-dwelling older adults (n=2857). Vitamin D deficiency was highly prevalent, with serum 25(OH)D concentrations <50 nmol/L in 45%, and <30 nmol/L in 14% of the population. When exploring the main determinants of serum 25(OH)D status, significant associations were observed with age, BMI, dietary intake, sun exposure behavior, and genetic polymorphisms encoding for enzymes in the vitamin D pathway. Combined, these factors explained 35% of the variation in serum 25(OH)D concentrations.

    To explore potential strategies that prevent vitamin D deficiency, we investigated the contribution of dietary vitamin D intake and specific food groups to serum 25(OH)D concentration in chapter 3. Daily vitamin D intake from dietary sources showed a median (25-75th percentile) intake of 4.0 (3.0-5.4) µg/day (n=595) and only 12-20% of older adults reported to take vitamin D supplements. These findings are in sharp contrast with the current nutrient guidelines and show that the vast majority of older adults do not meet the reference intakes for vitamin D. Nevertheless, significant associations were observed between the highest tertile of dietary vitamin D intake and serum 25(OH)D concentration, suggesting that regular intake of foods rich in vitamin D can support the prevention of modest insufficiency.

    For the majority of older adults, supplementation is required to ensure sufficient serum 25(OH)D concentrations throughout the year. Currently, supplementation with vitamin D3 is the most common strategy. However, alternative treatment regimens exist that require further investigation. In chapter 4, we report on a dose-response trial (n=59) that investigated the efficacy of calcifediol (5, 10 or 15 µg/d) as a supplementation strategy. Compared to vitamin D3, calcifediol is more hydrophilic, does not require hepatic hydroxylation, and binds with higher affinity to its binding proteins. In our study, we observed that calcifediol was safe and well tolerated in the supplemented doses over the entire study period of 6-months. We concluded that a dose of 10 µg/day resulted in sustained serum 25(OH)D concentrations between 75-100 nmol/L. Furthermore, calcifediol had a ~3 times higher potency when compared to vitamin D3, in increasing serum 25(OH)D concentrations. All in all, calcifediol may offer a valuable supplementation regimen to rapidly correct deficiency.

    Vitamin D presents an important endocrine regulator in the musculoskeletal health of older adults. Besides its role in bone health, low serum 25(OH)D concentrations have been linked to impaired physical performance and increased risk of falling. The active metabolite 1,25-dihydroxyvitamin D is suggested to act upon a wide variety of cells throughout the body, including muscle cells. Although the exact mechanisms by which vitamin D acts on muscle are unclear, several indirect or direct regulatory pathways have been described, including effects of 1,25-dihyroxyvitamin D through intracellular calcium and phosphate homeostasis, or via activation of transcription factors when binding to the vitamin D receptor in muscle cells.

    In chapter 5 we observed significant associations between low serum 25(OH)D concentrations, physical performance and frailty in community-dwelling older adults (n=494-756). However, randomized trials are needed to define the causality of the observed associations. A previous pilot study indicated plausible beneficial effects of calcifediol over vitamin D3 on performance and strength. As such, we aimed to further explore the potential role of calcifediol or vitamin D3 on muscle function in chapter 6. We performed a placebo-controlled trial in pre-frail and frail, vitamin D deficient older adults, supplementing either 10 µg/d calcifediol or 20 µg/d vitamin D3, compared to placebo over a 6-month period (n=78). Again, calcifediol induced a faster and higher increase in serum 25(OH)D status when compared to vitamin D3. However, we observed no effect of either supplementation regimen on lower extremity strength or physical performance. Current literature suggests positive effects on strength and balance when supplementing with vitamin D, however, results are inconsistent. Meta-analyses of randomized trials indicate that the beneficial effects of vitamin D supplementation might be more pronounced in vulnerable populations with more severe vitamin D deficiencies.

    All in all, the high prevalence of vitamin D deficiency is alarming. Promoting adequate vitamin D status is important considering the beneficial effects on bone health. In the last decade, research has come a long way in exploring the role of vitamin D in muscle function. However, the evidence base remains uncertain and further research on the optimal vitamin D status for older adults is needed to guide clinical practice. Until then, focus should be placed on prevention and identification of deficiency.

    Nutritional interventions to preserve skeletal muscle mass
    Backx, Evelien M.P. - \ 2016
    Wageningen University. Promotor(en): Lisette de Groot; L.J.C. van Loon. - Wageningen : Wageningen University - ISBN 9789462579149 - 158
    musculoskeletal system - nutritional intervention - skeletal muscle - vitamin d - creatine - leucine - nandrolone - protein intake - young adults - elderly - overweight - athletes - preservation - skeletspierstelsel - maatregel op voedingsgebied - skeletspier - vitamine d - creatine - leucine - nandrolon - eiwitinname - jongvolwassenen - ouderen - overgewicht - atleten - behoud

    Muscle mass is the main predictor for muscle strength and physical function. The amount of muscle mass can decline rapidly during periods of reduced physical activity or during periods of energy intake restriction. For athletes, it is important to maintain muscle mass, since the loss of muscle is associated with decreased muscle strength, decreased physical performance and a longer recovery period. In the older and more clinically compromised populations, the consequences of muscle loss can substantially impact metabolic health, physical functioning, quality of life and mortality rates. In this thesis, the effects of different nutritional interventions on the preservation of muscle mass are being evaluated.

    Vitamin D deficiency (serum 25-hydroxyvitamin D or 25(OH)D) has been associated with increased muscle loss and reduced muscle strength. In chapter 2, we identified seasonal changes in 25(OH)D concentration in elite athletes. We observed that 25(OH)D concentrations were highest at the end of summer (113±26 nmol/L), and lowest at the end of winter (78±30 nmol/L). Athletes that had a sufficient 25(OH)D concentration (>75 nmol/L) at the start of the study, still had a high risk (20%) of being deficient (<50 nmol/L) in late winter. Thus, a sufficient 25(OH)D concentration in summer does not guarantee a sufficient status in winter. In chapter 3, we assessed 25(OH)D concentrations in 128 highly-trained athletes and found that 70% had a deficient or insufficient 25(OH)D concentration at the end of the winter season. Supplementation with 2200 IU/d vitamin D resulted in a sufficient 25(OH)D concentration in 80% of the athletes after 12 months and was therefore a better dosage to improve 25(OH)D concentration than 400 or 1100 IU/d.

    In the following chapters, we assessed the effects of creatine supplementation (chapter 4), leucine supplementation (chapter 5) and nandrolone administration (chapter 6) on the preservation of muscle mass during a short period of muscle disuse. For all of these compounds there is prior evidence for their efficacy in augmenting muscle mass and strength gains in combination with resistance-type exercise training and all have been suggested to attenuate the loss of muscle mass during a period of muscle disuse. During 7 days of single-leg immobilization, muscle mass decreased by ~6% and muscle strength decreased by ~8%. Surprisingly, none of the tested compounds attenuated the loss of muscle mass during 7 days of single-leg immobilization in healthy, young men.

    In chapter 7, we performed a fully controlled dietary intervention to assess the impact of a high protein intake on the preservation of lean body mass during 12 weeks of energy intake restriction. Sixty-one overweight and obese men and women were randomly assigned to either a high protein diet (1.7 g/kg/d) or a normal protein diet (0.9 g/kg/d) during 12 weeks of 25% energy intake restriction. During the dietary intervention, subjects lost 9±3 kg body weight with a concomitant 2±2 kg decline in lean body mass with no differences between the two intervention groups. Thus, increasing protein intake above habitual intake levels (0.9 g/kg/d) did not preserve lean body mass during a period of energy intake restriction.

    Finally, in chapter 8 we reflected on the main findings described in this thesis. In this chapter, we point out that the populations studied were all healthy and well-nourished. We conclude that in these populations, additional creatine, leucine and protein beyond habitual intakes did not preserve muscle mass. Older and/or malnourished individuals might be more responsive to these nutritional interventions. Future research could also focus on the combined effects of two or more nutritional compounds during disuse that are known to affect different mechanisms. Moreover, we speculate that the tested nutritional compounds could be effective in accelerating the regain of muscle mass and strength after a period of muscle loss. However, it should be noted that muscle loss during disuse occurs at a rate that is several-fold greater than muscle (re)gain during resistance type exercise training. Therefore, it is imperative that we continue our endeavors to identify nutritional or pharmaceutical compounds or exercise mimetics that may help to prevent or attenuate disuse atrophy.

    Vitamin D-tour : cognition and depression: the role of vitamin D and its interplay with glucose homeostasis
    Brouwer-Brolsma, E.M. - \ 2014
    Wageningen University. Promotor(en): Lisette de Groot; Edith Feskens, co-promotor(en): Teun Schuurman; Wilma Steegenga. - Wageningen : Wageningen University - ISBN 9789462571082 - 215
    vitamine d - depressie - glucose - homeostase - gezondheid - hersenen - vitaminetekorten - vitamin d - depression - glucose - homeostasis - health - brain - vitamin deficiencies

    According to recent estimations approximately 35.6 million people have dementia worldwide. Globally, 350 million people experience one or more depressive episodes during their life. As the therapeutic options for dementia and depression are limited, these conditions form a major challenge for public health and society. More and more researchers have initiated research on potential preventive factors for dementia and depression, including the potential effects of nutritional factors. The aim of this PhD-thesis was to study the role of vitamin D and its potential interplay with glucose homeostasis, in the development of cognitive decline and depression, using epidemiological data as well experimental animal data.

    Chapter 2 recapitulates a debate between vitamin D experts that was organized to make a step towards the harmonization on the formulation of optimal vitamin D intake levels and serum 25(OH)D concentrations across Europe. It was concluded that based on the current evidence-base 25(OH)D concentrations ≥50 nmol/L are sufficient with respect to optimal bone health. For health outcomes beyond bone health evidence was considered insufficient to formulate optimal levels. In order to achieve and maintain a 25(OH)D concentration ≥50 nmol/L, older adults aged ≥65 years were recommended to adhere to a vitamin D intake of 20 μg/day.

    Chapter 3 shows that there is a high prevalence of 25(OH)D inadequacy in a population of Dutch older adults that participated in the B-PROOF study (n=2857), namely 45% had 25(OH)D concentrations <50 nmol/L. Mean vitamin D intake was 4.9±2.9 µg/day and only 20% of the participants reported to use vitamin D containing supplements. Exploration of the determinants of 25(OH)D status showed significant associations between vitamin D ‘raising’ SNPs (n=2530), higher sun exposure (n=1012), vitamin D intake (n=596) and higher 25(OH)D concentrations. Including all the potential relevant predictors in one model explained 35% of the variance in 25(OH)D status (R2=0.35).

    In chapter 4 the associations between 25(OH)D status and global cognitive performance (n=116), depressive symptoms (n=118), and surrogate markers of glucose intolerance (n=593) were evaluated using data of European adults aged 70-75 years. None of the associations reached significance.

    Studying the potential role of vitamin D in domain-specific cognitive performance and depression in 127 Dutch pre-frail and frail older adults aged ≥65 years (chapter 5), showed an association between 25(OH)D concentration and executive functioning, and a tendency towards an association with information processing speed. Stratification for ‘low’ and ‘high’ fasting glucose concentrations did not suggest an interaction between vitamin D and glucose homeostasis in the association with domain-specific cognitive performance. Moreover, adding fasting glucose or insulin did not substantially influence the associations between 25(OH)D status and domain-specific cognitive performance, and hence a mediation effect of glucose homeostasis was considered unlikely.

    We furthermore observed associations of 25(OH)D status with attention and working memory (n=787) (chapter 6), depression (n=2839) (chapter 7) and grey matter volume of the brain (n=217) (chapter 8) in a population community-dwelling Dutch older adults aged ≥65 years. Again, these studies did not provide evidence that the associations were modified or mediated by glucose intolerance. However, it should be emphasized that glucose intolerance in these three chapters was defined sub-optimally, specifically using blood samples that may have been collected in a non-fasting state, or by using self-reported diabetes data. Hence, the mediation and interaction effects should be interpreted cautiously.

    Finally, chapter 9 shows the results of a proof of principle study on the effect of a long-term vitamin D deficiency on cognitive decline and emotional reactivity in old C57BL/6j mice. Modest tendencies were shown for a relation between vitamin D and spatial learning, but these tendencies did not reach significance. Vitamin D deficiency did not affect recognition memory, spatial memory or emotional reactivity. Mice that received a higher dietary fat load, which was given to induce an impaired glucose tolerance, did not respond differently to a vitamin D deficiency than mice that received a low fat diet did.

    Overall, it is concluded that the evidence for an effect of vitamin D on cognitive performance/decline, depression or brain volume is insufficient to formulate disease specific cut-off values for vitamin D intake or 25(OH)D status. However, given the high prevalence of 25(OH)D concentrations <50 nmol/L we do call for a more active promotion of the current vitamin D intake recommendations.

    Vitamine B12, D, foliumzuur en leeftijdgerelateerde aandoeningen
    Brouwer, E.M. ; Wijngaarden, J.P. van - \ 2011
    Voeding Nu 4 (2011)13. - ISSN 1389-7608 - p. 20 - 21.
    ouderen - botbreuken - gezondheidsbescherming - ziektepreventie - vitaminen - supplementen - foliumzuur - vitamine b12 - vitamine d - deficiëntie - voeding en gezondheid - elderly - bone fractures - health protection - disease prevention - vitamins - supplements - folic acid - vitamin b12 - vitamin d - deficiency - nutrition and health
    Dat vitaminen en mineralen een positieve invloed uit kunnen oefenen op specifieke lichaamsprocessen is bekend. Twee promovendi van Wageningen Universiteit richten zich op het mogelijke verband tussen vitamine B12, foliumzuur en vitamine D en verschillende leeftijdgerelateerde aandoeningen. De associatie tussen een verhoogd homocysteïnegehalte en een verhoogd risico op fracturen was aanleiding voor een groot trial onderzoek onder ouderen. Dit B-PROOF onderzoek loopt nog.
    Vitaminen in rantsoenen voor biologisch melkvee = Fat soluble vitamins in rations for organic dairy cows en goat
    Smolders, G. ; Eekeren, N.J.M. van; Neijenhuis, F. - \ 2005
    Lelystad : Animal Sciences Group (PraktijkRapport / Animal Sciences Group, Praktijkonderzoek : Rundvee ) - 39
    melkvee - geiten - melkveehouderij - biologische landbouw - vitaminen - voedingsrantsoenen - diervoeding - diervoedering - bèta-caroteen - vitamine d - vitamine e - rundveevoeding - kennis - dairy cattle - goats - dairy farming - organic farming - vitamins - feed rations - animal nutrition - animal feeding - beta-carotene - vitamin d - vitamin e - cattle feeding - knowledge
    On five organic dairy cow farms during the period spring 2004/2005 feedstuffs and blood samples were taken 3 times to analyse beta carotene, vitamin D and vitamin E (tocopherols). On 3 organic dairy goat farms feeds and blood samples were taken only in spring 2005. Within types of feeds there are large differences in vitamin content. Vitamin shortages are not to be expected during the grazing season. During the housing period shortages of vitamin D and E might occur in dry cow and in fresh calved cows. In cow, coming into heat sometimes was a problem. On one of the goat farms animal health was not optimal. Rations with a variety of good quality grass silage, artificial dried grass or whole plant silage do not need extra supplementation of vitamins. For supplementation of rations with natural vitamin E plants rich in vegetable oil can be used, supplementation of diets with vitamin D could be found in sun cured products.
    Vergelijkend onderzoek op ratten en kuikens over de identiteit van het kunstmatige antirachitische vitamine (bestraald ergosterol) en het natuurlijke vitamine D uit kabeljauw-levertraan
    Dols, M.J.L. - \ 1935
    Wageningen University. Promotor(en): G. Grijns. - Nijmegen : Centrale Drukkerij - 139
    vitamine d - ratten - vleeskuikens - soortverschillen - vitamin d - rats - broilers - species differences
    Cod liver oil 2% sufficed to protect chickens against rickets, but irradiated ergosterol equivalent in rat units of vitamin D, equivalent to 20 % cod liver oil, was not sufficient. No single fact pointed to the presence of another factor in cod liver oil being indispensable besides vitamin D to protect chickens against rickets.

    Unsaponifiable matter from cod liver oil, irradiated cholesterol or concentrate from tunny liver oil, all in rat units of vitamin D equivalent to 2 % cod liver oil were within limits of experimental error equally protective against rickets in chickens. Crystalline irradiated ergosterol was not identical with vitamin D from cod liver oil. The provitamin D in cholesterol, activated antirachitically by ultraviolet irradiation, was not ergosterol. Requirement of vitamin D by chickens from the 1st till the 75th day, either as cod liver oil or as tunny liver oil concentrate or of irradiated cholesterol was 250 IU per 100 g ration, about 80 IU daily per chicken.

    To find rickets in chickens, radiography sometimes yields more information than examination of the skeleton post mortem. The average ash content of the tibiae was not a reliable comparison of the antirachitic efficiency of vitamin D preparations in chickens.

    De invloed van D-vitamine en ultra-violette bestraling bij verschillende verhoudingen van Ca:P in het dieet
    Groeneveld, B.J.B. - \ 1932
    Wageningen University. Promotor(en): G. Grijns. - Wageningen : Veenman - 74
    zoötechniek - fysiologie - chemie - metabolisme - lichaamssamenstelling - biochemie - anabolisme - fosfor - vitamine d - arsenicum - chemische analyse - blootstelling - milieuafbraak - kinetica - ecotoxicologie - zootechny - physiology - chemistry - metabolism - body composition - biochemistry - anabolism - phosphorus - vitamin d - arsenic - chemical analysis - exposure - environmental degradation - kinetics - ecotoxicology
    Two series of experiments with, respectively, 72(32♂ and 40♀) and 36 (all♀) spotted rats examined the influence of UV radiation and vitamin D on Ca and P metabolism. The experiments started at weaning of the rats (21-28 days) and lasted for 7 weeks in the first and for 5 weeks in the second series. Rations were used with Ca:P ratios varying between 1:045 and 1:2.8. Growth curves, skeletal X-ray photographs and Ca and P balances were studied.
    Ca: P ratios between 1: 0.96 and 1: 1.27 proved optimum. Net absorption and retention of these minerals was maximum at that ratio. The rations with extreme Ca: P ratios induced rachitis that healed with both treatments. It was in these rations that net absorption of Ca reacted most sensitively to vitamin D or UV treatment. At all Ca: P ratios some reaction was observed with vitamin D and with UV-treatment. Excess of one of the two minerals inhibited the retention of the other. Inhibition by Ca was more potent than by P.
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