PlOS Med:肥胖导致人体内维生素D不足

2013-02-17 PlOS Medicine 中国网 刘海英

  过去有研究显示,维生素D缺乏与肥胖二者之间有关联,但到底是维生素D缺乏导致了肥胖,还是肥胖导致体内维生素D不足,却一直没有明确。最近,英国伦敦大学学院儿童健康研究所的一项新研究对此因果关系进行了确认。该研究表明,肥胖会导致体内维生素D不足,而补充维生素D却起不到减肥的效果。   这一发表在《公共科学图书馆 医学》杂志上的研究,通过对42000人的遗传标记进行分析,探讨了身体质量指数(BMI)


  过去有研究显示,维生素D缺乏与肥胖二者之间有关联,但到底是维生素D缺乏导致了肥胖,还是肥胖导致体内维生素D不足,却一直没有明确。最近,英国伦敦大学学院儿童健康研究所的一项新研究对此因果关系进行了确认。该研究表明,肥胖会导致体内维生素D不足,而补充维生素D却起不到减肥的效果。

  这一发表在《公共科学图书馆 医学》杂志上的研究,通过对42000人的遗传标记进行分析,探讨了身体质量指数(BMI)与维生素D代谢、合成的关系,并通过超过123000人的生理数据来确认所得的研究成果。

  研究人员分析发现,BMI指数若提高10%,则会使得体内维生素D的浓度下降4%。据此研究人员认定,BMI指数过高,即肥胖,会导致维生素D不足,而维生素D缺乏对体重的影响则很小,二者关系不受性别、年龄等因素的影响。

  维生素D不足是个日益严重的公共健康问题。有证据表明,维生素D的代谢、存储等都会受到体内脂肪的影响。小鼠实验证实,大剂量的维生素D2可以促进体内能量的燃烧,但补充维生素D并不能起到减肥效果。

  研究人员表示,虽然许多研究表明缺乏阳光照射或过度使用防晒霜会造成维生素D缺乏,但也需注意,肥胖同样会引起维生素D不足;尽管补充维生素D不能帮助调节体重,但维生素D缺乏则会增加肥胖所带来的一系列健康问题的风险。


Background
Obesity is associated with vitamin D deficiency, and both are areas of active public health concern. We explored the causality and direction of the relationship between body mass index (BMI) and 25-hydroxyvitamin D [25(OH)D] using genetic markers as instrumental variables (IVs) in bi-directional Mendelian randomization (MR) analysis.
Methods and Findings
We used information from 21 adult cohorts (up to 42,024 participants) with 12 BMI-related SNPs (combined in an allelic score) to produce an instrument for BMI and four SNPs associated with 25(OH)D (combined in two allelic scores, separately for genes encoding its synthesis or metabolism) as an instrument for vitamin D. Regression estimates for the IVs (allele scores) were generated within-study and pooled by meta-analysis to generate summary effects.
Associations between vitamin D scores and BMI were confirmed in the Genetic Investigation of Anthropometric Traits (GIANT) consortium (n = 123,864). Each 1 kg/m2 higher BMI was associated with 1.15% lower 25(OH)D (p = 6.52×10−27). The BMI allele score was associated both with BMI (p = 6.30×10−62) and 25(OH)D (−0.06% [95% CI −0.10 to −0.02], p = 0.004) in the cohorts that underwent meta-analysis. The two vitamin D allele scores were strongly associated with 25(OH)D (p≤8.07×10−57 for both scores) but not with BMI (synthesis score, p = 0.88; metabolism score, p = 0.08) in the meta-analysis. A 10% higher genetically instrumented BMI was associated with 4.2% lower 25(OH)D concentrations (IV ratio: −4.2 [95% CI −7.1 to −1.3], p = 0.005). No association was seen for genetically instrumented 25(OH)D with BMI, a finding that was confirmed using data from the GIANT consortium (p≥0.57 for both vitamin D scores).
Conclusions
On the basis of a bi-directional genetic approach that limits confounding, our study suggests that a higher BMI leads to lower 25(OH)D, while any effects of lower 25(OH)D increasing BMI are likely to be small. Population level interventions to reduce BMI are expected to decrease the prevalence of vitamin D deficiency.

    

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