Dietary Super-Doses of Cholecalciferol Fed to Aged Laying Hens Illustrates Limitation of 24,25-Dihydroxycholecalciferol Conversion

BackgroundOlder humans who take high levels of vitamin D3 supplementation for a prolonged time may be at risk of vitamin D toxicity. It is unclear how dietary super-doses (10,000x greater than requirement) can affect vitamin D3 status in aged animals. Aged laying hens could be a model to compare vitamin D3 supplementation effects with women in peri- or postmenopausal stages of life.ObjectiveWe investigated dietary super-dose impacts of cholecalciferol (vitamin D3) on vitamin D3 status in aged laying hens in production.MethodsForty-eight 68 wk old Hy-Line Brown laying hens were individually housed in cages with eight hens per dietary treatment for eleven weeks. Hens were randomly assigned to one of six treatment groups of dietary vitamin D3 supplementation and fed ad libitum. Supplementation levels were 400, 800, 7,400, 14,000, 20,000, and 36,000 IU D3/kg of feed. At the end of the study, all hens were euthanized and tissue samples and feces were collected. Plasma and egg yolk vitamin D3 metabolites, calcium and phosphorus composition of eggshells, ileal digesta, and feces were measured. Duodenal, ileal, liver, and kidney gene expression levels were measured.ResultsWe observed that increasing dietary vitamin D3 increased plasma vitamin D3 and egg yolk vitamin D3 (p < 0.0001 for both sites). We also observed an increase in plasma 24,25-dihydroxycholecalciferol as dietary vitamin D3 levels increased (p < 0.0001). The plasma 25-hydroxycholecalciferol:24,25-dihydroxycholecalciferol ratio exhibited an asymptotic relationship starting at the 14,000 IU/kg D3 treatment.ConclusionsDietary super-doses of vitamin D3 led to greater plasma and egg yolk vitamin D3 levels which shows that aged laying hens can deposit excess vitamin D3 in egg yolk. We suggest future research should explore how 24-hydroxylation mechanisms are affected by vitamin D3 supplementation. Further understanding of 24-hydroxylation can help ascertain ways to reduce risk of vitamin D toxicity. Older humans who take high levels of vitamin D3 supplementation for a prolonged time may be at risk of vitamin D toxicity. It is unclear how dietary super-doses (10,000x greater than requirement) can affect vitamin D3 status in aged animals. Aged laying hens could be a model to compare vitamin D3 supplementation effects with women in peri- or postmenopausal stages of life. We investigated dietary super-dose impacts of cholecalciferol (vitamin D3) on vitamin D3 status in aged laying hens in production. Forty-eight 68 wk old Hy-Line Brown laying hens were individually housed in cages with eight hens per dietary treatment for eleven weeks. Hens were randomly assigned to one of six treatment groups of dietary vitamin D3 supplementation and fed ad libitum. Supplementation levels were 400, 800, 7,400, 14,000, 20,000, and 36,000 IU D3/kg of feed. At the end of the study, all hens were euthanized and tissue samples and feces were collected. Plasma and egg yolk vitamin D3 metabolites, calcium and phosphorus composition of eggshells, ileal digesta, and feces were measured. Duodenal, ileal, liver, and kidney gene expression levels were measured. We observed that increasing dietary vitamin D3 increased plasma vitamin D3 and egg yolk vitamin D3 (p < 0.0001 for both sites). We also observed an increase in plasma 24,25-dihydroxycholecalciferol as dietary vitamin D3 levels increased (p < 0.0001). The plasma 25-hydroxycholecalciferol:24,25-dihydroxycholecalciferol ratio exhibited an asymptotic relationship starting at the 14,000 IU/kg D3 treatment. Dietary super-doses of vitamin D3 led to greater plasma and egg yolk vitamin D3 levels which shows that aged laying hens can deposit excess vitamin D3 in egg yolk. We suggest future research should explore how 24-hydroxylation mechanisms are affected by vitamin D3 supplementation. Further understanding of 24-hydroxylation can help ascertain ways to reduce risk of vitamin D toxicity.