Enhanced Calcium Intake Increases Bone Mineral Density on the Background of Vitamin A Toxicity in a Swine Model.

BACKGROUND

Hypervitaminosis A inhibits bone mineralization. Additional calcium (Ca) may mitigate the negative impacts of excessive dietary vitamin A (VA).

OBJECTIVES

This study determined the effects of high dietary Ca on bone formation and growth in swine receiving varying concentrations of dietary VA, including the National Research Council (NRC) recommendation (2200 IU VA/kg feed for 5-11 kg pigs).

METHODS

Pigs were weaned on day 17 and randomly assigned by sex, weight, and litter to 5 treatments (n = 12/group): -VA=Ca, low VA, control Ca; =VA=Ca, NRC control; +VA-Ca, high VA, low Ca; +VA=Ca, high VA, control Ca; and +VA+Ca, high VA, high Ca for 5 wk. Weights and feed intake were measured weekly. VA was measured in serum, liver, and extrahepatic tissues using ultraperformance liquid chromatography. Bone mineral density (BMD) was assessed by dual-energy X-ray absorptiometry on the femurs. Outcomes were compared among treatments using linear mixed-effects models.

RESULTS

Weight gain was affected by treatment (P < 0.05) and was higher in -VA=Ca and +VA+Ca (0.44 ± 0.039 kg/d, 0.44 ± 0.043 kg/d, respectively) than +VA-Ca (0.35 ± 0.06 kg/d). The -VA=Ca and =VA=Ca groups were deficient (<0.1 μmol VA/g liver). Mean liver VA in +VA groups were >3.0 μmol/g, and 100% +VA-Ca and +VA+Ca pigs, and 91.7% of +VA=Ca pigs had fasting retinyl esters >5% of total serum VA, both indicating toxicity. The plasma concentrations of Ca and phosphorus in +VA+Ca were higher than all groups (P < 0.05) except +VA=Ca. BMD was highest in +VA+Ca (0.639 ± 0.048 g/cm2), and lowest in +VA-Ca (0.354 ± 0.035 g/cm2) (P < 0.0001).

CONCLUSIONS

VA fed at the NRC recommendation for 5 wk did not achieve sufficient liver VA stores. Excessive Ca supported bone development and weight gain despite VA toxicity. Further investigations are needed to determine swine VA requirements to ensure adequacy.