VN: Micronutrients in Pregnancy (2007)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To compare the magnesium status of pregnant women following a plant-based diet to the one of women consuming an average Western diet.  Additionally, the occurrence of calf muscle cramps during pregnancy was assessed.
Inclusion Criteria:
  • Pregnant women from each trimester
  • Must have completed questionnaire
  • Single pregnancy (not pregnant with twins)
  • Not currently taking multivitamin/mineral supplement
  • Living less than 200km from study site 
  • Women following a plant-based diet must have followed for at least 3 years prior to study.
Exclusion Criteria:
  • Metabolic diseases
  • Twin-pregnancy
  • Known pregnancy complications
  • Greater than three  previous deliveries
  • Concurrent use of medication that interacts with magnesium absorption (diuretics)
  • Magnesium supplementation prior to the study
  • Failure to complete questionnaire
  • Living greater than 200km from study site
Description of Study Protocol:


  •  Handouts in health magazines and gynecologists from 1995-1997


  • Blood sample and record of dietary intake for 4 days in weeks 9-12, 20-22, and 36-38
  • Women divided in 2 groups: Western Diet vs. vegetarian diet
  • Vegetarian diet divided further: lacto-ovo (those who did not consume any meat or meat products) vs low meat

Statistical Analysis

  •  Dietary intake was compared using the Mann-Whitney U-Test
  • Magnesium status of the dietary groups was compared by using generalized estimating equations (GEE).  All two-way interactions were tested, but no interactions with P<0.15 were found.  GEE model adjusted for BMI; for serum and red blood cell magnesium also adjusted for use of magnesium supplements, serum potassium and calcium concentrations.
Data Collection Summary:

Timing of Measurements

 Gestation wks 9-12, 20-22, 36-38

Dependent Variables

  • Serum, red blood cell, and urinary magnesium assessed from fasting blood draws and first morning urine collection respectively at each visit.  Magnesium was assessed within 2 hours of collection of serum and urine.
  • Calf muscle cramps assessed from information obtained from "complaint diary" developed for the study.

Independent Variables

  •  Dietary intake assessed using the German Food Code and Nutrition Data Base BLS II.3 from 4-day food record obtained at each visit


Description of Actual Data Sample:


Initial N: 119

Attrition (final N): 108 (38 following Western diet; 27 lacto-ovo diet; 43 low-meat eaters), 82 assessed for calf muscle cramps

Age: mean 29-30 years

Ethnicity: Not disclosed

Anthropometrics: BMI slightly higher in Western diet group than plant-based diet group 

Location: Glessen, Germany


Summary of Results:

 Dietary Intake of Magnesium

Dietary Intake/ Food Group

Lacto-Ovo Vegetarian (OLV)


Mean ±s.e.

Low-Meat Eaters (LME)


Mean ±s.e.

Western Diet


Mean ±s.e.

Statistical Significance of OLV vs Western diet

Statistical Significance of LME vs Western diet

Magnesium (mg/day)






Whole grain products
























Soy products






Magnesium intake was higher in the ovo-lacto vegetarians and low-meat eaters than in the control group.

Serum, Red Blood Cell, and Urinary Concentrations of Magnesium



mean ± s.e.


mean ± s.e.

Control Diet

mean ± s.e.

OLV vs. control


LME vs control


Serum Magnesium (mmol/l)

1 Trimester

2 Trimester

3 Trimester






















 Red Blood Cell  Magnesium (mmol/l)

1 Trimester

2 Trimester

3 Trimester

















 Urinary Magnesium (mmol/l)

1 Trimester

2 Trimester

3 Trimester


















Urinary magnesium was highest in ovo-lacto vegetarians (P=0.023), followed by low-meat eaters (P=0.017) compared to control group.

Dietary magnesium intake per body weight was positively related to the magnesium concentrations in serum (r=0.158; P=0.010), red blood cell (r=0.163, P=0.008) and in urine (r=0.219; P<0.001).

Observed magnesium concentrations for all participants were in the lower reference range.

Other Findings

Steady increase in calf muscle cramps reported.  During the first trimester, 4% of all subjects reported muscle cramps.  These reports were similar between all groups.  The second trimester had 17% of subjects reporting calf muscle cramps and by the third trimester, 48% of subjects.  The occurrence of calf cramps was significantly lower in the ovo-lacto vegetarians and low-meat eaters than in the control group during the second (P=0.011) and the third trimester (P=0.008).  The frequency of calf muscle cramps reported were also higher in the control group (58%) than the plant based diet group (24%, P=0.004). 

Serum magnesium concentrations were slightly lower in subjects reporting calf cramps than in subjects not reporting calf-cramps (0.67±0.06 vs 0.70±0.05 mmol/l, P=0.054).  No significant differences were found for magnesium concentrations in RBC in urine.


Author Conclusion:

During the course of pregnancy, women following a plant-based diet for an average of more than 8 years had a higher dietary intake of magnesium and also a higher nutrient density for magnesium than women on the control diet.  The higher dietary intake was not associated with a concurrent higher magnesium concentration in serum but serum magnesium concentrations are strictly regulated by the kidney.

Low serum magnesium concentrations even after a high magnesium intake in pregnant women adhering to a plant-based diet may be the high phytic acid intake from whole grain products.

Urinary magnesium excretion was markedly increased in the plant-based diet group when compared to the control group suggesting a higher bioavailability of magnesium in the ovo-lacto vegetarians and low-meat eaters.

No association was observed between protein intake and magnesium concentrations in serum or red blood cell.

It has been shown that measurement of total serum or plasma magnesium may not adequately reflect physiologic magnesium stores because plasma contains <1% of total body magnesium which is stored predominantly intracellular and in bone.

Our observations suggest higher magnesium intake of women following a plant-based diet is associated with a lower occurrence of calf muscle cramps.

The present study suggests that a habitual plant-based diet result in a slightly improved magnesium status during pregnancy compared to an average Western diet.

Funding Source:
Foundation associated with industry:
Reviewer Comments:

As dietary intake is highly based on ethnicity, it would be of importance to know in greater detail the demographics of the women following the Western diet versus the plant-based diet.  As diets high in saturated fats, sugar, caffeine, and alcohol may increase magnesium needs, a more detailed nutrient breakdown of the dietary records would be beneficial.  Ionized magnesium (IMg) is considered a better indicator of magnesium status than total serum concentations. 

Adult serum magnesium levels: 1.6-2mg/dl or 0.66-1.07mmol/l

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) N/A
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) N/A
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? No
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? ???
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? No
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? Yes