Dietary calcium does not interact with vitamin D₃ in terms of determining the response and catabolism of serum 25-hydroxyvitamin D during winter in older adults.
BACKGROUND
Interactions between calcium and vitamin D may have implications for the regulation of serum 25-hydroxyvitamin D [25(OH)D] and its catabolism and, consequently, the vitamin D dietary requirement.


OBJECTIVE
We investigated whether different calcium intakes influenced serum 25(OH)D and indexes of vitamin D activation and catabolism during winter and in the context of both adequate and inadequate vitamin D intakes.


METHODS
A 15-wk winter-based, randomized, placebo-controlled, double-blind vitamin D₃ intervention (20 μg/d) study was carried out in free-living men and women aged ≥50 y (n = 125) who were stratified according to calcium intakes [moderate-low (<700 mg/d) or high (>1000 mg/d) intake]. The serum 25(OH)D concentration was the primary outcome, and serum calcium, parathyroid hormone (PTH), 1,25-dihydroxyvitamin D [1,25(OH)₂D], 24,25-dihydroxyvitamin D [24,25(OH)₂D], the ratio of 24,25(OH)₂D to 25(OH)D, vitamin D-binding protein, and free 25(OH)D were exploratory outcomes.


RESULTS
A repeated-measures ANOVA showed there was no significant (P = 0.2) time × vitamin D treatment × calcium intake grouping interaction effect on the mean serum 25(OH)D concentration over the 15-wk intervention period. Serum 25(OH)D concentrations increased (P ≤ 0.005) and decreased (P ≤ 0.002) in vitamin D₃ and placebo groups, respectively, and were of similar magnitudes in subjects with calcium intakes <700 mg/d (and even <550 mg/d) compared with >1000 mg/d. The response of serum PTH, 1,25(OH)₂D, 24,25(OH)₂D, the ratio of 24,25(OH)₂D to 25(OH)D, and free 25(OH)D significantly differed in vitamin D₃ and placebo groups but not by calcium intake grouping.


CONCLUSIONS
We found no evidence of a vitamin D sparing effect of high calcium intake, which has been referred to by some authors as "vitamin D economy." Thus, recent dietary vitamin D requirement estimates will cover the vitamin D needs of even those individuals who have inadequate calcium intakes.
From the School of Food and Nutritional Sciences (KMS, AH, SMO, JYZ, M Kinsella, KG, M Kiely, and KDC) and the Department of Medicine (KDC), University College Cork, Cork, Ireland.
Kevin D
KD
Cashman
From the School of Food and Nutritional Sciences (KMS, AH, SMO, JYZ, M Kinsella, KG, M Kiely, and KDC) and the Department of Medicine (KDC), University College Cork, Cork, Ireland.
Aoife
A
Hayes
From the School of Food and Nutritional Sciences (KMS, AH, SMO, JYZ, M Kinsella, KG, M Kiely, and KDC) and the Department of Medicine (KDC), University College Cork, Cork, Ireland.
Sinead M
SM
O'Donovan
From the School of Food and Nutritional Sciences (KMS, AH, SMO, JYZ, M Kinsella, KG, M Kiely, and KDC) and the Department of Medicine (KDC), University College Cork, Cork, Ireland.
Joy Y
JY
Zhang
From the School of Food and Nutritional Sciences (KMS, AH, SMO, JYZ, M Kinsella, KG, M Kiely, and KDC) and the Department of Medicine (KDC), University College Cork, Cork, Ireland.
Michael
M
Kinsella
From the School of Food and Nutritional Sciences (KMS, AH, SMO, JYZ, M Kinsella, KG, M Kiely, and KDC) and the Department of Medicine (KDC), University College Cork, Cork, Ireland.
Karen
K
Galvin
From the School of Food and Nutritional Sciences (KMS, AH, SMO, JYZ, M Kinsella, KG, M Kiely, and KDC) and the Department of Medicine (KDC), University College Cork, Cork, Ireland.
Mairead
M
Kiely
From the School of Food and Nutritional Sciences (KMS, AH, SMO, JYZ, M Kinsella, KG, M Kiely, and KDC) and the Department of Medicine (KDC), University College Cork, Cork, Ireland.
Kelly M
KM
Seamans
D015650:24,25-Dihydroxyvitamin D 3 / Q000097:blood / Q000378:metabolism; D015652:25-Hydroxyvitamin D 2 / Q000097:blood* / Q000378:metabolism; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D002112:Calcifediol / Q000097:blood* / Q000378:metabolism; D002117:Calcitriol / Q000097:blood / Q000378:metabolism; D002118:Calcium / Q000097:blood / Q000378:metabolism; D002136:Calcium, Dietary / Q000008:administration & dosage / Q000378:metabolism / Q000627:therapeutic use*; D002762:Cholecalciferol / Q000378:metabolism / Q000627:therapeutic use*; D019587:Dietary Supplements; D004311:Double-Blind Method; D004872:Ergocalciferols / Q000097:blood / Q000378:metabolism; D005260:Female; D006801:Humans; D007494:Ireland; D008297:Male; D008875:Middle Aged; D009751:Nutritional Requirements; D012621:Seasons; D014808:Vitamin D Deficiency / Q000097:blood / Q000209:etiology / Q000378:metabolism / Q000517:prevention & control*
D002136:Calcium, Dietary; D004872:Ergocalciferols; D002762:Cholecalciferol; D015652:25-Hydroxyvitamin D 2; D015650:24,25-Dihydroxyvitamin D 3; C003564:1,25-dihydroxyergocalciferol; C028140:24,25-dihydroxyvitamin D2; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium