Associations of polymorphisms in vitamin D and iron-related genes with vitamin D supplementation and iron status in women

Abstract

Current evidence to guide and support nutrition recommendations is limited. Precision nutrition is a novel field of study that could direct patient protocols toward improving health outcomes using food as medicine. The discipline of nutrigenetics analyzes how the response to nutritional changes may vary depending on one’s alleles. Single nucleotide polymorphisms (SNPs) are small genetic variants that can contribute to physiological response. However, the effects of SNPs for all known alleles are not fully understood. During a three-week study, volunteers adhered to a vegan or vegetarian diet and ingested a vitamin D supplement (400 IU) daily in the latter two weeks. Blood samples were collected at the end of week one, prior to supplementation, as well as on the last day of the study. Samples were then analyzed for plasma calcidiol, hepcidin, and ferritin levels with ELISA assays, as well as used for DNA variant analysis in PCR and Sanger sequencing. The main finding in this study was that two weeks of 400 IU vitamin D supplementation did not significantly alter plasma calcidiol, hepcidin, or ferritin. There were also no significant interactions among supplementation response percent change scores. Most participants in the study had calcidiol levels in the suboptimal range. There was a minor positive correlation between BMI and plasma ferritin. Hormone therapy and menstrual cycle regularity appeared to influence baseline levels of hepcidin and ferritin. Hepcidin levels were lower in participants reporting no hormone therapy compared to those with hormone therapy, regardless of menstrual regularity. Irregular menstrual cycling was associated with higher baseline ferritin. SNP analyses revealed haplotype variations in baseline and responses to vitamin D supplementation for calcidiol, hepcidin, and ferritin, but significant differences among haplotypes were undeterminable given low and unequal sample sizes. These findings merit further study with a larger sample size, higher vitamin D dose, and longer time frame.