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Effet de la vitamine D sur les marqueurs métaboliques et la fonction musculaire : étude chez des sujets libanais âgés, normo-pondéraux ou obèses

Abstract : The main role of vitamin D is to control the homeostasis of the phosphorus and calcium status of the body. Recent observational studies have shown that vitamin D is also able to regulate insulin secretion and insulin sensitivity, thus playing an important role in the regulation of glucose homeostasis. In addition, vitamin D has been shown to modulate muscle health. For example, vitamin D deficiency negatively influences muscle mass and muscle function in the elderly. Studies have clearly shown that correcting vitamin D deficiencies improves muscle contractile function and muscle strength in this population. In addition, the level of physical activity decreases with age, that negatively affects muscle mass and contractile function, and leads to weight gain, mainly due to increased body fat. However, studies have found that overweight seniors are characterized by lower blood vitamin D levels, lower muscle mass and strength compared to a reference age population.The main objective of this work was to evaluate the effects of vitamin D supplementation on glucose homeostasis and insulin resistance index, as well as on appendicular muscle mass (ASMM) and muscle strength in normal weight or overweight older people. This work is based on a randomized controlled trial, performed in single blind. In terms of results, we show that vitamin D intake in normal or overweight elderly subjects, characterized by a low vitamin D status, improved short-term fasting glucose and insulin resistance markers. The increase in serum 25-hydroxyvitamin D [25 (OH) D] after supplementation resulted in a significant decrease in fasting insulin levels and in HOMA-IR index. We were able to identify a correlation between low serum concentrations of [25 (OH) D] and a decrease in glucose tolerance and an increased risk of type 2 diabetes.Regarding muscle markers, we have shown that vitamin D supplementation has beneficial implications on appendicular muscle mass and fat mass in elderly men and women. However, we found no significant effect on muscle strength. We also found that overweight subjects had a lower serum [25 (OH) D] at baseline. In addition the increase in muscle mass after vitamin D intake was lower in this group than in normal weight subjects.Overall, this work shows that it is necessary to monitor the vitamin D status in older people, especially in overweight subjects.
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Cynthia El Hajj. Effet de la vitamine D sur les marqueurs métaboliques et la fonction musculaire : étude chez des sujets libanais âgés, normo-pondéraux ou obèses. Alimentation et Nutrition. Université Clermont Auvergne, 2019. Français. ⟨NNT : 2019CLFAS015⟩. ⟨tel-02521297⟩

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