Estimation of the 25(OH) vitamin D threshold below which secondary hyperparathyroidism may occur among African migrant women in Paris.

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.