Journal of the American College of Nutrition, Vol. 17, No. 4, 385-387 (1998)
Published by the American College of Nutrition
Glucose Ingestion and Whole Blood Ionized Calcium and Magnesium in the Third Trimester of Pregnancy
Luis A. Bracero, MD,
Francis Mimouni, MD, FACN and
Attiya Hafeez, MD
Department of Obstetrics and Gynecology (L.A.B., A.H.), Maimonides Medical Center, Brooklyn, NY
Department of Pediatrics (F.M.), Maimonides Medical Center, Brooklyn, NY
Address reprint requests: Luis A. Bracero, MD, Dept. OB/GYN, Catholic Medical Center, 88-25 153rd Street, Suite 4G, Jamaica, NY 11432
 |
ABSTRACT
|
|---|
Objective: To test the hypothesis that glucose ingestion leads to a decrease in plasma ionized calcium (iCa) and ionized magnesium (iMg) during the third trimester of pregnancy.
Methods: We studied 54 women who underwent a 50 g glucose challenge test (GCT) and 27 women who underwent a 3-hour 100 g glucose tolerance test (GTT) because of an abnormal GCT. Plasma glucose was measured with an automated chemistry analyzer, while whole blood iCa and iMg were measured using an ion-selective electrode.
Results: The 1-hour plasma glucose post-GCT correlated inversely with whole blood iCa (r=-0.322, p=0.027). The 3-hour plasma glucose GTT revealed a similar, but not statistically significant, decrease in blood iCa (r=-0.378, p=0.356). The combined 1-hour peak plasma glucose during GTT and GCT correlated inversely with iCa (r=-0.376, p=0.001), but not with iMg (r=0.050, p=0.737). Using multiple regression with iCa as the dependent variable and plasma glucose and glucose dose (50 or 100 g) as independent variables, both plasma glucose and glucose dose were inversely correlated with iCa (R2=0.45, p<0.001).
Conclusion: We conclude that in pregnancy, induced hyperglycemia correlates with a drop in blood iCa concentrations; however a 100 g glucose load leads to a lesser iCa decrease than a 50 g load.
Key words: pregnancy, ionized calcium, ionized magnesium, glucose tolerance
|
INTRODUCTION
|
|---|
Oral ingestion of glucose in adults and children leads to a decrease in plasma calcium [1,2]. Studies have shown that ingestion of glucose causes elevations in plasma gastrin and enteroglucagon concentrations which in turn elevate plasma calcitonin levels [3]. Increased calcitonin is known to cause hypocalcemia [4]. Data are lacking on the effects of glucose ingestion on whole blood total or ionized calcium (iCa) in pregnant women. Furthermore, there are no data on the effects of glucose ingestion on whole blood total or ionized magnesium (iMg).
The purpose of this study was to assess the effects of glucose ingestion on iCa and iMg concentrations in the third trimester. We hypothesized that glucose ingestion in pregnancy leads to a drop in whole blood iCa and iMg.
|
MATERIALS AND METHODS
|
|---|
This was a prospective study, conducted between 12/6/95 and 2/27/96, and approved by the Maimonides Medical Center Institutional Review Board. All pregnant women attending the obstetrical clinic at the Maimonides Medical Center were eligible for participation. Fifty-four pregnant women who were undergoing a 50 g glucose challenge test (GCT) between 24 and 28 weeks of gestation to screen for gestational diabetes were recruited for the study. Fifteen additional women who previously had an abnormal GCT and needed a 100 g 3-hour glucose tolerance test (GTT) were also asked to be participants. The mean gestational age at time of the GCT was 26.6±4.3 weeks, and at time of the GTT was 26.3±5.6. Informed consent was signed by all patients.
At the time of the GCT or GTT, 2 ml of blood was collected in heparinized tubes for analysis of whole blood iCa and iMg. Samples were refrigerated for a maximum of 6 hours prior to analysis. A Nova 8 Analyzer with an ion-selective electrode (Nova Biomedical, Waltham, MA) was used to measure iCa and iMg, and the results are reported as normalized for a pH of 7.40. Plasma glucose was measured with a Paramax automated chemistry analyzer (Baxter Diagnostics Inc., Deerfield, IL).
In this preliminary study, we intended to recruit approximately 30 women undergoing GTT because this sample size was considered adequate for detecting important correlations. Pearson correlation was used to assess the relationship between continuous variables. A Student’s t-test was used to compare independent continuous variables. Paired t-tests were used for comparisons of the GTT results. Multiple linear regression was used to control for the effects of potentially confounding factors, such as maternal weight or glucose dose on iCa or iMg. A p value of <0.05 was considered statistically significant.
|
RESULTS
|
|---|
Maternal characteristics are shown in Table 1. Twelve of 54 (22.2%) women had a GCT test result 
140 mg/dl. Nine of 27 (33.3%) women who underwent a GTT had an abnormal GTT, consistent with a diagnosis of gestational diabetes [5]. The concentrations of iCa after GCT ranged from 4.33 mg/dl to 5.53 mg/dl, with a mean value of 4.81±0.24 mg/dl. One hour post-GCT plasma glucose was inversely correlated with whole blood iCa (r=-0.322, p=0.027, Fig. 1). One-hour post-GCT plasma glucose values did not correlate with whole blood iMg (r=0.064, p=0.669).
View larger version (17K):
[in this window]
[in a new window]
|
Fig. 1. Inverse relationship between the 1-hour plasma glucose after 50 g glucola load (x axis, mg/dl) and whole blood iCa (y axis, mg/dl).
|
|
During the 3-hour GTT, there was a trend for a drop in blood iCa and iMg (Fig. 2) which did not reach statistical significance. However, the peak plasma glucose during GTT and GCT combined correlated inversely with simultaneously obtained blood iCa (r=-0.376, p=0.001, Fig. 3), but not with blood iMg. Using multiple regression analysis with iCa as the dependent variable and plasma glucose and glucose dose (50 vs. 100 g) as independent variables, both plasma glucose and glucose dose were inversely correlated with iCa (R2=0.45, p<0.001).
View larger version (18K):
[in this window]
[in a new window]
|
Fig. 2. Mean glucose, iCa, and iMg concentrations (y axis) during 3-hour GTT. While there are significant changes in plasma glucose, the decrease in iCa and iMg does not reach statistical significance.
|
|
To test whether the heaviest women had the smallest decrease in ionized calcium, we assessed the correlation between iCA and peak glucose for women below the median weight and then above the median weight. Both groups showed an inverse correlation but there was increased variability in the heavier women.
Using a Student’s t-test we found that women with a glucose concentration equal to or greater than 150 mg/dl had a statistically significantly lower iCa level when compared with those women with a glucose concentration less than 150 mg/dl (4.72 vs. 4.88 mg/dl, p=0.003).
|
DISCUSSION
|
|---|
We found that during pregnancy, ingestion of glucose correlates with a decrease in blood iCa concentration. In this pilot study we chose not to measure glucagon, gastrin, or calcitonin, because we were unsure whether blood iCa or iMg correlated with blood glucose concentration. We can only speculate that, similar to the non-pregnant state, ingestion of glucose during pregnancy leads to increased enteroglucagon and gastrin production with a subsequent increase in calcitonin production and then a drop in iCa concentration [2]. The absence of any relationship between glucose ingestion and iMg is not surprising. When purified porcine calcitonin was administered to humans, a decrease in magnesium concentration did not accompany the resulting hypocalcemia [6,7]. Shaul et al have also shown that Mg infusion does not result in significant change in plasma calcitonin [8]. The lack of statistical significance for the correlation between iMg and peak plasma glucose is unlikely to be due to the small sample size. With an r=0.05 the sample size would have to include 3138 patients to show statistical significance, assuming a power of 80% and a p value of 0.05. Using these assumptions, the sample size required to show statistical significance for correlation between the iCa and peak plasma glucose was 54 patients; exactly the sample size that we obtained.
The greater hypocalcemic effect of a lower, rather than a higher, dose of ingested glucose is paradoxical and difficult to explain. We speculate that with the higher glucose dose of 100 g, a greater degree of hyperglycemia leads to an inhibition of pancreatic glucagon production. This in turn may oppose the effects of gastrin and enteroglucagon (stimulated by glucose ingestion) on calcitonin.
The results of this study must be considered as preliminary. While it appears that glucose ingestion significantly affects iCa concentrations, the mechanism is still speculative. Our results may be relevant to a number of disease states which complicate pregnancy and in which a role for dietary calcium has been suggested such as pregnancy induced hypertension [9], a frequent complication of pregnancies in women with diabetes [10].
Received January 1, 1997.
Accepted December 1, 1997.
|
REFERENCES
|
|---|
- Londono JH, McGee JH, Sobel RE, et al. Variations in serum calcium and phosphorus levels during glucose tolerance tests. Clin Chem
17:
648,
1971.
- Venkataraman PS, Blick KE, Rao R, Fry HD, Parker MK: Decline in serum calcium, magnesium, and phosphorus values with oral glucose in normal neonates: Studies of serum parathyroid hormone and calcitonin. J Pediatr
108:
607–610,
1986.[Medline]
- Swaminathan R, Bates RLF, Bloom SR, Ganguli PC, Care AD: The relationship between food, gastrointestinal hormones and calcitonin secretion. J Endocrinol
59:
217–230,
1973.[Abstract/Free Full Text]
- Stevenson JC, Hillyard CJ, MacIntyre I, Cooper H, Whitehead MI: A physiological role for calcitonin: protection of the maternal skeleton. Lancet
ii:
769–770,
1979.
- National Diabetes Data Group: Classification and diagnosis of gestational diabetes mellitus and other categories of glucose intolerance. Diabetes
28:
1039–1057,
1979.[Medline]
- Bell NH, Barrett R, Patterson R: Effects of porcine thyrocalcitonin on serum calcium, phosphorus and magnesium in the monkey and in man. Proc Soc Exper Biol Med
123:
114–118,
1966.[Medline]
- Foster GVI, MacIntyre I, Joplin GF, Melum KEW: Effect of Thyrocalcitonin in man. Lancet
1:
107–109,
1966.[Medline]
- Shaul PW, Mimouni F, Tsang RC, Specker BL: The role of magnesium in neonatal calcium homeostasis: Effects of magnesium infusion on calciotropic hormones and calcium. Ped Res
22:
319–323,
1987.[Medline]
- Villar J, Repke J, Belizan JM, Pareja G: Calcium supplementation reduces blood pressure during pregnancy: results of a randomized controlled clinical trial. Obstet Gynecol
70:
317–322,
1987.[Medline]
- Siddiqi T, Rosenn B, Mimouni F, Khoury J, Miodovnid F: Hypertension during pregnancy in insulin-dependent diabetic women. Obstet Gynecol
77:
514–519,
1991.[Abstract/Free Full Text]
TOP
ABSTRACT
INTRODUCTION
