title: Vitamin D Status Is Positively Associated with Calcium Absorption among Postmenopausal Thai Women with Low Calcium Intakes.
abstract: BACKGROUND
  Few data exist on the ability of postmenopausal women to absorb calcium from diets habitually low in calcium.
  
  
  OBJECTIVE
  The objective of this study was to evaluate fractional calcium absorption from a green leafy vegetable vs. milk in relation to vitamin D status.
  
  
  METHODS
  We measured fractional calcium absorption from both a dairy- and plant-based source in 19 postmenopausal Thai women (aged 52-63 y) with low calcium consumption (350 ± 207 mg/d) in relation to serum parathyroid hormone (PTH) and serum 25-hydroxyvitamin D [25(OH)D]. Fractional calcium absorption was measured using a triple stable calcium isotope method based on isotope recovery in a 28-h urine collection. Two extrinsically labeled test meals were ingested in random order: a green leafy vegetable (cassia) ingested along with ⁴³Ca or a glass of milk containing ⁴⁴Ca. Women received intravenous ⁴²Ca with the first test meal.
  
  
  RESULTS
  In 19 postmenopausal women studied (mean age, 56.9 ± 3.4 y), ~95% were 25(OH)D sufficient (≥20 μg/L). Serum 25(OH)D status was positively correlated with fractional absorption from both cassia (P = 0.05, R² = 0.21) and milk (P = 0.03, R² = 0.26). Fractional calcium absorption from cassia was significantly lower than that measured from milk (42.6% ± 12.3% vs. 47.8% ± 12.8%, P = 0.03), but true calcium absorption did not significantly differ (120 ± 35 mg/d vs. 135 ± 36 mg/d). Serum PTH was significantly inversely associated with serum 25(OH)D (P = 0.006, R² = 0.37) even though PTH was not elevated (>65 pg/mL).
  
  
  CONCLUSIONS
  These findings suggest that vitamin D status is an important determinant of calcium absorption among Thai women with low calcium intakes, and cassia may be a readily available source of calcium in this population. Furthermore, these data indicate that serum 25(OH)D concentrations may affect PTH elevation in postmenopausal women with low calcium intakes.
authors: Institute of Nutrition, Mahidol University, Nakhon Pathom, Thailand; and.
authors: Prapaisri P
authors: PP
authors: Sirichakwal
authors: Institute of Nutrition, Mahidol University, Nakhon Pathom, Thailand; and.
authors: Achiraya
authors: A
authors: Kamchansuppasin
authors: Division of Nutritional Sciences, Cornell University, Ithaca, NY.
authors: Christine C
authors: CC
authors: Akoh
authors: Institute of Nutrition, Mahidol University, Nakhon Pathom, Thailand; and.
authors: Wantanee
authors: W
authors: Kriengsinyos
authors: Institute of Nutrition, Mahidol University, Nakhon Pathom, Thailand; and.
authors: Somsri
authors: S
authors: Charoenkiatkul
authors: Division of Nutritional Sciences, Cornell University, Ithaca, NY koo4@cornell.edu.
authors: Kimberly O
authors: KO
authors: O'Brien
mesh_terms: D000368:Aged; D000375:Aging; D000818:Animals; D015415:Biomarkers / Q000097:blood / Q000652:urine; D002127:Calcium Isotopes; D002136:Calcium, Dietary / Q000032:analysis / Q000378:metabolism*; D002366:Cassia; D004032:Diet / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism*; D008875:Middle Aged; D008892:Milk; D009752:Nutritional Status; D017698:Postmenopause; D019518:Postprandial Period; D015995:Prevalence; D012306:Risk; D013785:Thailand / Q000453:epidemiology; D014675:Vegetables; D014808:Vitamin D Deficiency / Q000097:blood / Q000453:epidemiology / Q000378:metabolism* / Q000652:urine
chemical_list: D015415:Biomarkers; D002127:Calcium Isotopes; D002136:Calcium, Dietary
keywords: bioavailability; calcium absorption; parathyroid hormone; postmenopausal women; stable isotope; vitamin D