Increased calcium intake is associated lower serum 25-hydroxyvitamin D levels in subjects with adequate vitamin D intake
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RESEARCH ARTICLE
Open Access
Increased calcium intake is associated lower serum 25-hydroxyvitamin D levels in subjects with adequate vitamin D intake: a population-based observational study Rolf Jorde1,2* and Guri Grimnes1,2
Abstract Background: There are indications that an increased intake of calcium has a vitamin D sparing effect, which might be explained by a decreased catabolism of 25-hydroxyvitamin D (25(OH)D). However, there are only a few studies where this has been examined. Method: In the seventh survey of the Tromsø study, serum 25(OH)D and parathyroid hormone were measured, and questionnaires on calcium and vitamin D intakes filled in. Results: There were significant interactions between sex, calcium and vitamin D intakes regarding serum 25(OH)D level. The analyses were therefore done stratified. In males there was, regardless of vitamin D intake, a significant decrease in serum 25(OH)D with increasing calcium intake. The difference in serum 25(OH)D between those with the highest and lowest calcium intakes was approximately 10%. In the females, there was in subjects with low vitamin D intake (< 7 μg/d) a significant increase in serum 25(OH)D with increasing calcium intake, which could not be explained by secondary hyperparathyroidism. In females with higher vitamin D intakes, increasing calcium intake was associated with lower serum 25(OH)D levels. Conclusions: There is, at least in subjects with an adequate vitamin D intake, a negative association between calcium intake and serum 25(OH)D. Keywords: Calcium, Parathyroid hormone, Vitamin D, 25-hydroxyvitamin D
Background Vitamin D is obtained from the diet or supplements and also from production in the skin upon sun exposure. Vitamin D is first hydroxylated in the liver to 25hydroxyvitamin D (25(OH)D), and then in the kidneys to 1,25-dihydroxyvitamin D (1,25(OH)2D) which is the active form of the vitamin. The main biological effect of 1, * Correspondence: [email protected] 1 Tromsø Endocrine Research Group, Department of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, Norway 2 Division of Internal Medicine, University Hospital of North Norway, 9038 Tromsø, Norway
25(OH)2D is to increase the intestinal calcium absorption. The 25-hydroxylation is substrate driven, whereas the 1hydroxylation is tightly regulated by parathyroid hormone (PTH). If the serum calcium level falls, the serum PTH level increase stimulating secretion of 1,25(OH)2D and thereby restoration of the serum calcium level [1]. The serum level of 25(OH)D is generally considered as the best marker of a subjects vitamin D status, due to its ease of measurement, long half-life and correlation with known vitamin D effects. However, there is no consensus as to what can be considered an adequate or optimal serum 25(OH)D level [2, 3].
© The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropri
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