Low Dietary Vitamin D with a Regular Level of Calcium Prior To and During Pregnancy and Lactation Has No Effect on Trabecular Bone Structure of Mouse Dams

Rationale Vitamin D and calcium are necessary for bone health. We have shown that maternal and post‐weaning exposure to low versus high levels of dietary vitamin D (25 versus 5000 IU/kg diet) alters structural outcomes of trabecular bone health in male (PMID: 27698344) but not female (PMID: 27792161) offspring while cortical bone was unaffected in both sexes. Of note was that offspring were challenged with an obesogenic diet (high fat and sucrose) to exacerbate effects on bone health from age 15 days through to 7 months. Our findings from these offspring suggest that calcium (Ca) can compensate for low dietary vitamin D intakes in rodents. Because pregnancy and lactation are a stress on maternal bone health, we conducted a follow‐up study and measured bone outcomes of the mothers at the end of lactation. The objective of this study was to determine if a maternal diet low in vitamin D, and previously shown to not impact bone structure in their female offspring, was sufficient to maintain BMD, bone structure and bone strength of mothers who had undergone pregnancy and lactation. Study Design & Methods 3‐week old female C57BL/6J mice were fed AIN93G diet containing 0.5% Ca and either 25 (low) or 5000 (high) IU vitamin D/kg diet through mating (at age 7 weeks), pregnancy and lactation (n=12/group). These levels are substantively lower and higher than the level of 1000 IU vitamin D/kg diet in the AIN93G diet. At the end of lactation, corresponding to an age of 13 weeks, mice were euthanized and femurs and lumbar vertebrae (LV) were collected. Femurs and LV outcomes were measured ex vivo : BMD of whole femur and 1/3 proximal femur using DXA (pSabre, Orthometrix), bone structure at the femur midpoint, distal femur and LV using micro computed tomography (Skyscan 1176, Bruker microCT) and bone strength at femur neck, femur midpoint and LV using a materials testing system (Model 4442, Instron Corp.). Results There were no differences in trabecular bone structure (BV/TV, Tb.Th., Tb.N., Tb.Sp., DA, Conn.Dn) at the distal femur or lumbar vertebra among mothers fed low or high vitamin D. For cortical bone at femur midpoint, Ct.Ar/Tt.Ar and Ec.Pm were lower (p<0.05) among mothers fed low versus high vitamin D while other measures (Tt.Ar., Ct.Ar., Ct.Th., Ps.Pm., Ecc.) were similar. Interestingly, bone mineral content (BMC) and BMD of whole femur and proximal 1/3 were similar while BMD but not BMC was lower (p<0.05) for LV with low vitamin D. However, bone strength, measured as peak load to fracture, did not differ between groups at all three sites measured. Conclusion Mothers fed low vitamin D from weaning through end of lactation have largely similar bone health to mothers receiving a high level of vitamin D. Given that bone health is similar between groups, regardless of the challenge of pregnancy and lactation to bone health, suggests that the level of Ca in the AIN93 diet may compensate for low vitamin D and/or that AIN93 diet contains levels of vitamin D far in excess of that needed to support a healthy bone structure in mice. Support or Funding Information Funding provided by Centrum Foundation Pfizer Consumer Healthcare Research Innovation Fund and the Department of Nutritional Sciences at the University of Toronto. Infrastructure support was provided from the Canada Foundation for Innovation (Grant # 222084). Christopher R. Villa was partially funded by the Banting and Best Diabetes Centre‐Novo Nordisk Studentship and Tamarack Graduate Award in Diabetes Research and by an Ontario Graduate Scholarship. Elena Comelli holds the Lawson Family Chair in Microbiome Nutrition Research at the University of Toronto. Wendy Ward holds a Canada Research Chair in Bone and Muscle Development.

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