Purpose: It has previously been shown that there is a threshold of serum 25-hydroxy vitamin D below which secondary hyperparathyroidism may occur. Our purpose was to estimate this threshold in a population of migrant African women living in Paris. Methods: Between February 2008 and December 2009, measurements of 25-hydroxy vitamin D and parathormone were performed in 165 African migrant women living in Paris. The estimation of 25-hydroxy vitamin D and parathormone marginal distributions as Gaussian mixtures, combined with a nonparametric kernel estimation method of the regression function of parathormone on 25-hydroxy vitamin D, provided the desired estimate of serum 25-hydroxy vitamin D threshold. Results: In our sample of African women, our method has shown that serum 25-hydroxy vitamin D levels below 48 ± 2 nmol/L may induce an increase in parathormone concentrations. Conclusion: In this sample, our method provided a reliable estimate (95 % confidence interval) of the serum 25-hydroxy vitamin D level below which an increase in parathormone concentrations can be observed. © 2011 Hans Huber Publishers.

25-hydroxyvitamin D Kernel regression Gaussian mixture African migrant women Secondary hyperparathyroidism

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