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Vegetarian Nutrition

VN: Therapeutic Vegetarian Diets and Attrition (2009)

Citation:
Hunt JR, Matthys LA, Johnson LK. Zinc absorption, mineral balance, and blood lipids in women consuming controlled lactoovovegetarian and omnivorous diets for eight weeks. Am J Clin Nutr. 1998 Mar; 67 (3): 421-430.
PubMed ID: 9497185
 
Study Design:
Non-Randomized Crossover Trial
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
  • Primary objective: Determine zinc absorption from a whole ovolactovegetarian diet and to relate the absorption results to measures of zinc status and excretion after an extended period (eight weeks) of consumption of a controlled diet
  • Additional objectives: Determine effect of ovolactovegetarian diet on
    • Balance of other minerals and tract elements
    • Blood pressure 
    • Plasma lipids and lipoproteins.
Inclusion Criteria:
  • Female
  • No apparent underlying diseases
  • Had not donated blood for more than six months
  • Had not used iron or zinc supplements exceeding 20mg per day for more than six months
  • Agreed to discontinue taking all nutrient supplements upon application submission (generally six to 12 weeks before start of study).
Exclusion Criteria:

None noted.

Description of Study Protocol:

Recruitment

Women recruited through public advertisements.

Design

Crossover trial.

Intervention

Registered dietitians planned two experimental diets (ovolactovegetarian and non-vegetarian) containing ordinary foods in a two-day menu cycle. 

  • The subjects consumed an ovolactovegetarian and a non-vegetarian diet for eight weeks each in a crossover design
  • All foods were weighed (to an accuracy of 1%) and provided by the research center
  • Women ate breakfast at the research center on weekday mornings and carried the remaining food to their homes or workplace in cooled, insulated containers; they reheated foods that were usually served warm before consuming them
  • To maintain individual body weights, energy intakes were adjusted in 200kcal increments by proportionally changing the amounts of all foods
  • Coffee and tea were excluded from the diets
  • City water, a low-energy carbonated water and chewing gum were consumed by subjects as desired after analyses indicated these foods had minimal trace element contents
  • Limited amounts of salt, pepper and selected low-energy carbonated beverages were provided individually according to the volunteers' preferences and then served consistently throughout the study (with corresponding adjustments made to mineral balance calculations)
  • The ovolactovegetarian and non-vegetarian diets contained zero and 184g meat per day (zero and approximately 6.5oz per day; mostly beef), respectively
  • In contrast with the non-vegetarian diet, the ovolactovegetarian diet contained legumes daily and included whole grain (rather than refined) bread and cereal products
  • Ovolactovegetarian diet contained slightly less saturated fat, approximately 100mg per day less cholesterol, approximately 25% less protein, 12% less fat, somewhat greater amounts of fruit and vegetables, 16% more carbohydrate, 21% more ascorbic acid, 2.5 times more dietary fiber and three times more phytic acid than the non-vegetarian diet
  • By analysis, calcium contents of the two diets were similar, but the ovolactovegetarian diet had approximately 45% more copper and magnesium, more than twice as much manganese, 10% less phosphorus, 14% less zinc (despite similar calculated amounts of zinc) and four times more total inositol phosphates than did the non-vegetarian diet. 

 Statistical Analysis

  • Dietary effects determined by repeated measures analysis of variance (ANOVA), with individual volunteers serving as their own controls
  • Variance in data expressed as a pooled standard deviation (SD), calculated as square root of mean square error from the ANOVA
  • Pearson's correlation coefficients used to assess additional relations between variables
  • Results significant when P<0.05
  • Non-significant P values between 0.05 and 0.11 were noted when judged to be of interest.

 

Data Collection Summary:

Timing of Measurements

  • Zinc absorption using extrinsic radioisotopic tracer measured after four weeks on each diet in subsample of 11 women
  • Zinc absorption via whole-body radioactivity determined before the meals, after second labeled meal and twice weekly thereafter
  • Blood pressure conducted two times weekly during weeks five to eight of each dietary period
  • Chemical analyses: Blood via phlebotomy obtained after overnight fast after week seven and eight on each diet
  • Mineral balances (via feces and urine collection) determined in all women for the last 14 days of each diet.

Dependent Variables

  • Variable One, zinc absorption
    • Measured via 65Zn as extrinsic radioisotopic tracer and by serial whole-body scintillation counting
    • Zinc measure using 65Zn as extrinsic radioisotopic tracer, measured on subsample of 11 women after four weeks on each diet, entire menu (three meals a day for two days; evening snack foods served with the third meal) was labeled with 7.4kBq 65Zn. Tracer mixed with foods in each meal that were the best sources of zinc, and the specific activity (ratio of 65Zn to elemental zinc) was constant for all meals. [Note: measurement on subsample provided adequate statistical power.]
    • Whole-body radioactivity was determined before the meals, after the second labeled meal and twice weekly thereafter.
  • Variable Two, mineral balance:
    • Plasma zinc and copper determined by atomic-absorption spectrophotometry
    • Plasma magnesium diluted with 0.5% lanthanum chloride before measurement by atomic-absorption spectrophotometry
    • Ceruloplasmin activity determined by colorimetrically measuring its p-phenylenediamine oxidase activity
    • Feces collected completely for last 14 days of each dietary test period: Calcium, copper, magnesium, manganese, phosphorus and zinc contents of digestates determined by inductively coupled argon-plasma-emission spectrophotometry
    • Urinary calcium, magnesium, phosphorus and zinc were similarly measured. Urinary copper and manganese were not determined because concentrations of these were below accurate detection limits by this method and did not contribute significantly to the balance determination. 
    • Elemental balance calculated as difference between dietary intake and excretion (in feces and urine)
    • Apparent absorption calculated as difference between dietary intake and fecal excretion
    • For subjects in whom zinc absorption was measured with radioisotopes, endogenous fecal zinc excretion estimated as fecal zinc minus unabsorbed dietary zinc (e.g., fecal zinc (dietary zinc to absorbed zinc)
    • Dietary inositol phosphates determined by HPLC
  • Variable Three, blood lipid concentrations: Apolipoprotein A-I and apolipoprotein B measured by immunochemical prescription. Lipoprotein(a) measured by automated immunoprecipitation analysis. Triacylglycerol determined by enzymatic hydrolysis and chromogenic coupling to measure glycerol. Total cholesterol determined by enzymatic hydrolysis, with oxidation and chromogenic coupling. HDL cholesterol determined after extraction with phosphotungstic acid. VLDL cholesterol estimated from triacylglycerol and LDL cholesterol determined by difference (LDL equals total HDL minus VLDL).  
  • Variable Four, blood pressure: Measured on left arm with automated microprocessor-based, oscillometric sphygmomanometer after subjects lain supine for more than 10 minutes in a quiet room.

Independent Variable

Diet: Ovolactovegetarian diet, non-vegetarian diet.

Description of Actual Data Sample:

 

  • Initial N: 21 females
  • Attrition (final N): 21 females
  • Age: 33.2±seven years (range, 20 to 42 years)
  • Ethnicity: Not reported
  • Other relevant demographics: None of the women used medications routinely, with the exception that nine used hormonal contraceptives.

Anthropometrics

  • Mean body weight: 62.1±8.4kg (range, 53kg to 82kg)
  • Body mass index (BMI): 23.5±2.8kg/m2 (range, 19.0kg/m2 to 29.0kg/m2).

Location

North Dakota, US.

 

Summary of Results:

Table One
The table below presents the plasma concentrations of trace elements, ceruloplasmin, blood lipids and lipoproteins and blood pressure for the two diet arms of the study.

Variables

Ovolactovegetaria

Non-Vegetarian

P-Value

1: Zinc Absorption1 (N=11)

(mg per day)

2.4

3.7

0.001

(Percentage of diet)

26

33

0.01

  Zinc balance (N=21)

Diet (mg per day)2

9.1±1.0

11.1±1.3

 

Urine (mg per day)

0.27

0.33

0.01

2: Plasma Concentrations of Minerals and Ceruloplasmin (N=21)

Zinc (umol per L)

13.9

14.7

0.05

Copper (umol per L)

21.5

23.2

0.001

 Ceruloplasmin (mg per L)

519

563

0.001

3: Plasma Concentrations of Blood Lipids and Lipoproteins (N=21)

HDL chol (mmol per L)

1.16

1.3

0.05

LDL chol (mmol pr L)

2.48

2.73

0.001

Total chol (mmol per L)

4.08

4.45

0.001

LDL : HDL ratio

2.24

2.23

NS

Total cholesterol : HDL ratio

3.63

3.56

NS

Apolipoprotein A-I (mg per L)

14.2

15.8

0.001

Apolipoprotein B (mg per L)

7.5

8.1

0.05

Lipoprotein(a) (mg per L)

1.61

1.83

0.05

Triacylglycerol (mmol per L)

0.96

0.9

NS

4: Blood Pressure

Systolic (mm Hg)

108

109

NS

Diastolic (mm Hg)

65

65

NS

Non-Vegetarian
1 Measured isotopically by whole-body counting and zinc balance
2 x+SD: Diet variability reflects individual differences in energy intake as well a analytic variability. ANOVA not conducted for dietary date detailed limited number of independent samples.

Table Two
Analyzed calcium, copper, magnesium, manganese and phosphorus balance1.


 

Ovolacto-vegetarian

Non-vegetarian

P-Value

Calcium  Diet

(mg per day)2

973+112

995+139

 
Urine

(mg per day)

119

155

0.0001

(Percentage of diet)

12

16

0.04

Copper Diet

(mg per day)2

1.8+0.2

1.3+0.2

 
Feces

(mg per day)

1.4

1

0.03

Magnesium Diet

(mg per day)2

367+44

260+29

 
Urine

(Percentage of diet)

27

34

0.02

Feces

(mg per day)

278

169

0.0001

(Percentage of diet)

76

65

0.02

Apparent absorption

(percentage of diet)

24

35

0.02

Manganese Diet

(mg per day)2

5.9+0.7

2.5+0.3

 
Feces

(mg per day)

5.3

2.4

0.0001

Phosphorus Diet

(mg per day)2

1,457+167

1,667+182

 
Urine

(mg per day)

745

1,011

0.002

(Percentage of diet)

51

60

0.03

Feces

(mg per day)

669

583

0.05

(Percentage of diet)

46

35

0.0003

Apparent absorption

(mg per day)

788

1,084

0.0001

(Percentage of diet)

54

65

0.0003

 
1 N=21
2 x+SD. Diet variability reflects individual differences in energy intake as well an analytic variability. ANOVA not conducted for dietary date detailed limited number of independent samples.
  • Tables One and Two above note significant differences of variables only (exception, Variable Four: Blood pressure, neither systolic nor diastolic blood pressure were significantly affected by diet)
  • Blood cholesterol and cholesterol fractions were significantly reduced by 8% to 11% (table one) with the ovolactovegetarian diet compared with non-vegetarian diet; however, the ratios of LDL to HDL or of total cholesterol to HDL were not significantly different, nor was triacylglycerol affected by diet
  • Despite higher copper content of the ovolactovegetarian diet, both concentrations of copper in plasma and activity of ceruloplasmin were significantly reduced by approximately 8% with ovolactovegetarian diet, compared with non-vegetarian diet
  • The apparent absorption of magnesium, expressed as a proportion of dietary magnesium, was significantly lower with the ovolactovegetarian diet (P<0.02). However, because the ovolactovegetarian diet contained substantially more magnesium than the non-vegetarian diet, magnesium balance was not significantly different between the two diet periods.
  • The lower absorption of phosphorus with the ovolactovegetarian diet was compensated for by a reduction of 266mg per day in urinary phosphorus excretion, thus phosphorus balance was unaffected by diet.

Other Findings

  • Estimated endogenous zinc excretion was not different between the two diets. Results suggested endogenous fecal zinc excretion was roughly in proportion to the amount absorbed from each diet, with no indication that excretion was increased when diet contained more phytic acid.
  • There was no correlation between zinc absorption (measured in week four) and plasma zinc concentration (measured Weeks Seven and Eight)
  • Plasma zinc concentrations did not correlate with urinary zinc excretion or zinc balance measured at the same time.
Author Conclusion:
  • There are two potential problems in obtaining adequate zinc from a vegetarian diet: Low zinc content of the diet and low zinc bioavailability. Both affected the results of this study.
  • Zinc balance was maintained with both diets. Although there is greater risk of zinc deficiency in persons consuming an ovolactovegetarian diet compared with omnivorous diets, with inclusion of whole grains and legumes, zinc requirements can be met and zinc balance maintained.
  • Although the ovolactovegetarian diet contained substantially more copper, magnesium and manganese than the non-vegetarian diet, only manganese balance was positively affected by this higher content
  • It appears urinary calcium excretion partially compensated for the nearly significant differences in apparent calcium absorption, and that with the substantial calcium intakes of nearly 1,000mg, the subjects were in balance when consuming both diets. The lower urinary calcium with the ovolactovegetarian diet in this study probably resulted from lower calcium absorption associated with phytic acid.
  • Results of this study suggest that vegetarian diets do not lower blood pressure under conditions of constant energy consumption and body weight.
Funding Source:
Government: USDA
Reviewer Comments:
  • Authors did not indicate if subjects were randomly assigned to a specific treatment order
  • No exclusion criteria were noted
  • No discussion of whether all subjects recruited were entered into the study
  • No discussion of attrition
  • Biases and study limitations were not discussed by authors
  • Unsure if duration of intervention was sufficient to produce a meaningful effect
  • No mention of a washout period between diets.
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) Yes
  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) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  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
  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) Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
  1. Was the research question clearly stated? Yes
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.1. 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
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? No
  1.3. Were the target population and setting specified? No
  2. Was the selection of study subjects/patients free from bias? No
2. Was the selection of study subjects/patients free from bias? No
  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? No
  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? No
  2.2. Were criteria applied equally to all study groups? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? No
  2.4. Were the subjects/patients a representative sample of the relevant population? No
  3. Were study groups comparable? Yes
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
  3.1. 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
  3.2. 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
  3.3. 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? N/A
  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? N/A
  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
  3.5. 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
  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. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  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
  4.2. 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
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
  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? No
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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.) No
  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.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  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
  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. 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? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? No
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? No
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  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? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  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? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? 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. 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
  7.1. 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
  7.2. 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? N/A
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? 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
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.7. Were the measurements conducted consistently across groups? 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. 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
  8.1. 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
  8.2. 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
  8.3. 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)? N/A
  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)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? 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? No
  8.6. Was clinical significance as well as statistical significance reported? No
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
  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? No
9. Are conclusions supported by results with biases and limitations taken into consideration? No
  9.1. Is there a discussion of findings? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? No
  9.2. Are biases and study limitations identified and discussed? No
  10. Is bias due to study's funding or sponsorship unlikely? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes
  10.2. Was the study free from apparent conflict of interest? Yes