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DLM: Major Dietary Components for LDL-Cholesterol Reduction (2001)

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

To examine trends in consumption of energy and fat, prevalence of overweight in the population, the association of overweight with levels of blood pressure (BP) and blood cholesterol (CHOL) and the prevalence of high BP and high CHOL among the overweight compared with the non-overweight across NHANES I, II and III surveys.

Inclusion Criteria:
  • Age 20 to 74 years old
  • Non-institutionalized civilians living in the United States.
Exclusion Criteria:

Less than three BP measurements taken with a standard sphygmomanometer either at home or in the medical examination center.

Description of Study Protocol:

Recruitment

Not applicable. This paper uses existing data sets to examine trends over time.

Design

  • Cross-sectional surveys (NHANES I, II, and III)
  • Each consisting of in-home interviews and medical examinations carried out in mobile units.

Statistical Analysis (Descriptive statistics after age-adjustments)

  • All analyses used the appropriate sample weights to produce national estimates
  • Age-adjustments:
    • BP estimates for NHANES III were age-adjusted to the 1990 US population
    • Estimates of CHOL levels were age-adjusted to the 1990 US population
    • Mean energy intake was age-adjusted
    • Age-adjusted and age-specific mean systolic BPs (SBP) and diastolic BPs (DBP) and mean total CHOL were estimated according to BMI level for men and women according to race
    • Age adjustments for trends between subgroups used the 1980 US population
  • Prevalence rates of high BP and high CHOL were calculated.
Data Collection Summary:

Timing of Measurements

  • NHANES I: 1971 to 1974
  • NHANES II: 1976 to 1980
  • NHANES III: 1988 to 1994
    • Phase I: 1988 to 1991
    • Phase II: 1993.

Variables

  • Dietary Intake:
    • Estimated from one 24-hour recall per person; conducted by trained nutritionists
    • In NHANES III, multiple-pass 24-hour recall developed by the University of Minnesota's Nutrition Coordinating Center was used
    • NHANES III also had an updated USDA nutrient database as the primary source of nutrient composition data
  • Blood pressure:
    • Two sets of three BP measurements were taken; one set by a trained and certified lay interviewer and the second by a trained physician at the mobile examination center 
    • High BP was defined as mean SBP greater than 140mmHg, mean DBP greater than 90mmHg or currently taking antihypertensive medication
  • CHOL:
    • Fasting blood draw obtained by venipuncture; standardized by using National Heart, Lung and Blood Institute (NHLBI)/CDC criteria
    • High blood cholesterol was defined as total serum cholesterol greater than 6.21mmol per L
  • Body weight and height:
    • Measured using standardized techniques and equipment
    • Adults were weighed without shoes in a hospital gown using an electronic-load cell scale in kilograms
    • Height was measured without shoes, using a fixed stadiometer and recorded to the nearest milimeter
    • Overweight was BMI 27.8kg per m2 or higher for men and 27.3kg per m2 or higher for women (sex-specific 85th percentile values of BMI for men and women age 20 to 29 years from NHANES II).

 

Description of Actual Data Sample:
  • Initial N: Not reported; tens of thousands participated in each survey
  • Age: 20 to 74 years old 
  • Ethnicity: Results reported for White and non-Hispanic Black men and women only 
  • Location: Throughout the US.

 

Summary of Results:

 

Variables

NHANES I

NHANES II

NHANES III (Phase 1)

 NHANES III (Phase 2) Trend

Age-adjusted Energy Intake (kcal Midpoints)

All Men: 2,465 

  • White (W): 2,492
  • Black (B): 2,240

All Women: 1,546

  • W: 1,560
  • B: 1,417

All Men: 2,457 

  • W: 2,488
  • B: 2,237

All Women: 1,531

  • W: 1,544
  • B: 1,446

 All Men: 2,465 

  • W: 2,492
  • B: 2,240

All Women: 1,546

  • W: 1,560
  • B: 1,417

 All Men: 2,751

  • W: 2,777
  • B: 2,553

All Women: 1,831

  • W: 1,838
  • B: 1,785
 Little difference except in NHANES III, data show an increase of ~300 kcal in men and women compared with NHANES I and II

Total Fat (grams) Intake

 All Men: 102.6

  • W: 104.0
  • B: 90.5

All Women: 63.1

  • W: 63.9
  • B: 57.1

 All Men: 101.5

  • W: 103.1
  • B: 91.0

All Women: 62.5

  • W: 63.1
  • B: 58.8

 All Men: 102.6

  • W: 104.1
  • B: 98.2

All Women: 69.3

  • W: 69.2
  • B: 70.5

 All Men: 105.4 

  • W: 107.3
  • B: 98.9

All Women: 69.0

  • W: 69.4
  • B: 68.9
  Between 1993 and 1972, fat intake increased ~2.8 g for men and about ~6g for women; There has been a greater increase in Black persons

Percent Energy from Fat (%)

 All Men: 36.8

  • W: 36.9
  • B: 36.2

All Women: 36.0

  • W: 36.1
  • B: 35.5

 All Men: 36.7

  • W: 36.8
  • B: 36.2

All Women: 35.9

  • W: 36.0
  • B: 35.9

 All Men: 34.3

  • W: 34.5
  • B: 34.2

All Women: 33.9

  • W: 33.9
  • B: 35.0

 All Men: 33.7

  • W: 34.1
  • B: 33.6

All Women: 32.9

  • W: 33.0
  • B: 33.5

Year 2000 goal of 30% of energy or less in total fat has not yet been met.

 Consistent downward trend in men and women; no significant difference between White and Black groups

Percent Energy from Saturated Fat (%)

All Men: 13.5

  • W: 13.6
  • B: 12.7

All Women: 12.9

  • W: 13.0
  • B: 12.4

All Men: 13.2 

  • W: 13.3
  • B: 12.8

All Women: 12.5

  • W: 13.0
  • B: 12.4

All Men: 11.7 

  • W: 11.9
  • B: 11.3

All Women: 11.6

  • W: 11.7
  • B: 11.7

All Men: 11.1 

  • W: 11.2
  • B: 10.9

All Women: 10.7

  • W: 10.9
  • B: 10.7

 Year 2000 goal of less than 10% of energy as saturated fat has not yet been met.

 Consistent downward trend in men and women; no significant difference between White and Black groups
Overweight (Prevalence of)  25.0  25.4  33.3    Changed from 1 in 4 in early 1970s to 1 in 3 in 1990; trend seen in all survey subgroups with highest prevalence among low-income women (45% to 50%)
Hypertension

 

  

 Overall: 24

  • B 32.4%
  • W: 23.3

% controlled by medication = 35% (Year 2000 goal is at least 50%)

   Increase in prevalence
High Blood Cholesterol  5.53mmol/L    5.33mmol/L    Decline for every sex and age group

Other Findings

Relation Between Overweight, High BP and High CHOL

BP and CHOL increase as BMI increases.

Age-adjusted Mean BP by BMI and Sex

  • Increase in mean DBP with increasing BMI in men and women that is similiar for Black and White populations
  • The difference between highest and lowest quintile of BMI category was:
    • ~ 7mmHg for DBP in men (80mmHg vs. 73mmHg) 
    • ~6 mmHg for DBP in women (75mmHg vs. 69mmHg)
    • ~8 mmHg for SBP in men (131mmHg vs. 124 mmHg)
    • ~11 mmHg for SBP in women.

Prevalence of High BP by BMI, Sex and Race

  • Prevalence of high BP increases in overweight people compared with non-overweight people; the trend is most prominent in White women and lowest in Black women.
  • Compared to non-overweight persons in the same demographic category, the increased prevalence of high BP is:
    • 75% in overweight White women
    • 20% in overweight Black women
    • 40% higher in White men
    • 60% higher in Black men.

Age-adjusted Mean CHOL by BMI and Sex

  • Men: Mean cholesterol intake level increased by ~0.49mmol per L from the lowest to highest quintile of BMI
    • Similiar trend for White and Black men
  • Women: Mean cholesterol level increased by ~19mg per dL from lowest to highest quintile of BMI
    • White women have higher mean levels than Black women at the upper BMI.

Prevalence of High CHOL by BMI, Sex and Race

  • Compared to non-overweight persons in the same demographic category, the increased prevalence of high CHOL is:
    • 20% in overweight White women
    • 10% in overweight Black women
    • 15% in overweight White men
    • 60% in overweight Black men.
Author Conclusion:
  • These data from NHANES surveys show that trends in overweight (BMI) differ from those of other cardiovascular heart disease risk factors (blood pressure and blood cholesterol levels) and dietary intakes
  • Mean dietary lipid intakes as a proportion of energy are nearing recommended levels, and there are improvements in the proportion of the population who have controlled their high blood pressure and cholesterol levels. However, there is a striking increase in the prevalence of overweight in the US.
Funding Source:
Government: NHLBI and CDC
Reviewer Comments:

Strengths:

  •  Representative and large sample of US adults

Limitations:

  • Between NHANES II and III, the dietary data collection method was improved substantially, so the observed increase in energy intake may be at least partially attributable to more complete intake information
  • Dietary intake data are underreported because a higher mean daily energy intake for a percentage of adults would be required to maintain body weight.
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? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? 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) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) 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? 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? 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%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? 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
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.) N/A
  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? Yes
  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? 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
  6.7. 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? No
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? No
  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
  8.6. Was clinical significance as well as statistical significance reported? 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
  9.1. 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? Yes
  10.2. Was the study free from apparent conflict of interest? Yes