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VN: Cardiovascular Disease (2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

The purpose of this study was to examine association of using different foods and the risk of cancer, ischemic heart disease and all-cause mortality, by comparing vegetarian and non-vegetarian groups.

Inclusion Criteria:

Seventh-Day Adventist, non-Hispanic Californian whites aged 25 or older, who returned lifestyle questionnaires in 1976.

Exclusion Criteria:

No exclusion criteria were stated.

Description of Study Protocol:

Recruitment

  • Recruitment began with a 1974 census questionnaire mailed to all Seventh-Day Adventist households in state of California
  • 59,081 Seventh-Day Adventists, aged 25 or older, were identified by the census and all were mailed a detailed lifestyle questionnaire in 1976
  • A 75% response rate of non-Hispanic whites yielded 34,198 participants for this study.

Design

Cohort study:

  • A surveillence program to detect new cancer and ischemic heart disease was conducted for six years
  • Relative risk of these diseases was calculated for each category (vegetarian, semi-vegetarian and non-vegetarian).

Statistical Analysis

Cohort study used relative risk at 95% CI.

Data Collection Summary:

Timing of Measurements

The dependent variable (incidence of cancer or ischemic heart disease) was measured annually through a six-year surveillence program.

Dependent Variables

  • The dependent variables, incidence of cancer or ischemic heart disease, were measured via cohort responses to annual mailings requesting information on any hospitialization in previous 12 months. If cancer or ischemic heart disease was reported, then the study personnel went back and reviewed the medical records to verify.
  • Other dependent variables reported as cross-sectional data were: Obesity, diabetes mellitus, hypertension and arthritis
  • Computerized matching with state death tapes and the National Death Index was used to identify fatal cases.

Independent Variables

  • Frequency of specific food and food groups eaten via a food frequency questionnaire, which included questions relating to 51 different foods or food groups. Select foods reported on were: Beef, poultry, fish, vegetarian meat substitutes, soft margarine on bread, eggs, doughnuts, coffee, tomatoes, legumes, nuts, green salads and fruit (all fruit and then fruit separated as canned, dried, citrus, winter and other).
  • Categorization of cohorts into "Vegetarian" (ate no fish, poultry, or meat), "Semi-Vegetarians" (ate fish and poultry, but less than once a week) and "Non-Vegetarians" (all remaining subjects).

Control Variables

  • Multi-variate analysis was adjusted for age, sex, smoking, exercise, BMI and hypertension when examining the impact of beef consumption and nut consumption on ischemic heart disease. Additionally, bread, nuts, fish, cheese, coffee, legumes and fruit consumption was adjusted when examining the impact of beef in the diet. When examining the impact of nut consumption, the same food consumption adjustments were made except beef was adjusted in place of nuts as previously listed.
  • Analysis of diabetes, hypertension and arthritis by vegetarian status was adjusted for age
  • Analysis of incidence of common cancers in vegetarians vs. non-vegetarians was adjusted for age and sex and in the case of lung cancer, for past and present smoking
  • Analysis of fruit consumption and all incidence of lung cancers in California Seventh-Day Adventists was adjusted for age, sex and cigarette-smoking history.
Description of Actual Data Sample:
  • Initial N: 34,198 (13,857 male; 20,341 female)
  • Attrition (final N): 3% lost to follow-up, however all of these subjects contributed some person-years
  • Age: 25 to over 85 years
  • Ethnicity: Non-Hispanic white
  • Other relevant demographics: Seventh-Day Adventists
  • Anthropometrics: In this group of 45- to 60-year-olds, male non-vegetarians weighed an average of 6.4kg more than their vegetarian counterparts. Female non-vegetarians weighed an average of 5.5kg more than the vegetarians. Average BMIs of these groups showed statistical significance between vegetarians and non-vegetarians.
  • Location: Residents of the State of California.
Summary of Results:

Baseline data suggests both male and female Seventh-Day Adventist vegetarians have lower risks of diabetes mellitus, hypertension and arthritis than non-vegetarians, however this may not be attributed only to the absence of meat, but perhaps other specific dietary practices.

Odds Ratio and 95% CIs of Prevalent Diabetes, Hypertension and Arthritis by Vegetarian Status in California Seventh-Day Adventists1

Endpoint

Vegetarians

Semi-Vegetarians

Non-Vegetarians

Diabetes; Male

1.00

1.35 (1.02, 1.78)2

1.97 (1.56, 2.47)2

Diabetes; Female

1.00

1.08 (0.89, 1.32)2

1.93 (1.65, 2.25)2

Hypertension; Male

1.00

1.57 (1.36, 1.83)2

2.23 (1,96, 2.52)2

Hypertension; Female

1.00

1.44 (1.30, 1.59)2

2.24 (2.05, 2.44)2

Rheumatoid Arthritis; Male

1.00

1.14 (0.83, 1.56)3

1.50 (1.16, 1.95)3

Rheumatoid Arthritis; Female

1.00

1.16 (0.97, 1.39)2

1.57 (1.35, 1.83)2

Rheumatism; Male

1.00

1.20 (1.03, 1.39)2

1.48 (1.31, 1.68)2

Rheumatism; Female

1.00

1.28 (1.16, 1.41)2

1.61 (1.49, 1.75)2

1: Adjusted for age
2,3: Significantly different from vegetarians, 2P=0.0001; 3P=0.005.

Cohort Study

  • Beef consumption of three or more times per week for men showed RR of 2.31 for fatal ischemic heart disease over vegetarians, however no associations were found between beef consumption and fatal ischemic heart disease in women
  • Those who ate nuts four or five times per week had only about 50% of ischemic heart disease risk vs. those who ate nuts once a week or not at all, regardless of whether they were vegetarian or not
  • Those who used whole grain bread had RR of 0.89 for fatal ischemic heart disease (P<0.005) and 0.56 for non-fatal ischemic heart disease (P<0.01) vs. those who used white bread
  • Both colon and prostate cancer were significantly more common among non-vegetarian Seventh-Day Adventists
  • Both red and white meat conumption increased the risk of colon cancer
  • There were no clear dietary associations with breast cancer in this study population.

Incidence and RR of Common Cancers in Non-Vegetarians vs. Seventh-Day Adventist Vegetarians1

Cancer

Incidence (N)

Relative Risk (95% CI)

P-Value

Colon

107

1.88  (1.24, 2.87)

0.0032

Breast

128

1.25 (0.87, 1.80)

0.22

Lung2

45

1.16 (0.56, 2.38)

0.69

Prostate

127

1.54 (1.05, 2.26)

0.03

Uterine

1.16

1.17 (0.81, 1.71)

0.41

1: Non-vegetarians ate meat more than once a week; vegetarians ate no meat. Adjusted for age and sex.
2: Also adjusted for past and present smoking.

  • A strong inverse association was found between eating fruit and the risk of lung cancer, i.e, eating fruit three times per week or less had an RR of 1.00 for development of lung cancer, whereas eating fruit up to once a day had an RR of 0.30 and eating fruit at least twice a day had an RR of 0.26
  • Seventh-Day Adventist vegetarians had an RR for total mortality of 0.80, CI 95%, compared with those who ate any meat products.
Author Conclusion:
  • Vegetarian Seventh-Day Adventists are at an advantage over their non-vegetarian counterparts, as they are less likely to develop cancers of the colon, prostate and fatal heart disease in men
  • Odds ratios of this study group suggests that there is also an advantage of decreased development of diabetes mellitus, hypertension and arthritis
  • In this study, the advantages are related to both the reduced consumption of meat and the increased consumption of fruit, vegetables, whole grains and nuts by vegetarians.
Funding Source:
Government: NIH
Reviewer Comments:

The cross-sectional data and cohort study report suggest that Seventh-Day Adventists with vegetarian dietary habits (reduced meat consumption and increased fruit, vegetable, whole grain and nut consumption) are less likely to develop colon and prostate cancer and fatal ischemic heart disease in men, as well as diabetes mellitus, hypertension and arthritis.

Strengths

  • The author made his comparisons within the special population (Seventh-Day Adventists), which reduced the likelihood of confounding by other non-dietary factors, such as absence of tobacco and limited use of alcohol
  • There was a large population (N=34,198), which yielded about 180,000 person-years and satisfactory statistical power for several common cancers such as breast, colon and prostate.
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? Yes
  1.3. Were the target population and setting specified? Yes
  2. Was the selection of study subjects/patients free from bias? 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
  2.1. 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
  2.2. 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? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
  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? 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.) 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.) Yes
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? Yes
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? Yes
  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? 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%.) No
  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%.) No
  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? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? Yes
  5. Was blinding used to prevent introduction of bias? Yes
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
  5.1. 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
  5.2. 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? No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  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? N/A
  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? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  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? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
  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? 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
  7.4. 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? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  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)? 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
  8.5. 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
  8.6. 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
  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. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  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? 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. 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