HTN: Vitamins (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To determine whether dietary vitamin E intake in childhood (four years of age) or mid-life (43 years of age) was predictive of adult hypertension and high waist circumference.
Inclusion Criteria:
Singleton, legitimate births in England, Scotland or Wales during the first week of March 1946; N=5,362
Exclusion Criteria:
  • Those not interviewed at 43 years and those from whom dietary records were not collected at both time points (four and 43 years) were excluded
  • 2,980 remained in the study
  • It was felt that the population was still representative of the native-born population.
Description of Study Protocol:

Recruitment

  • The 1946 British Birth Cohort of the MRC National Survey of Health and Development was used. It is a social class-straified random sample of 5,362 singleton legitmate births in England, Scotland or Wales occurring during the first week of March 1946.
  • No further information regarding recruitment is given.

Design

Longitudinal study with two time points of data collection: At four and at 43 years.

Statistical Analysis

  • Energy-adjusted tertiles of vitamin E intake were calculated and six categories of vitamin E intake were defined (low, middle, high at childhood or adulthood)
  • Using low vitamin E intake at childhood and adulthood as the reference group, differences were analyzed using multiple logistic regression to determine odds ratios adjusted for confounding variables with 95% confidence intervals and significance designated at P<0.05
  • Univariate analyses (chi square, ANOVA) tests were used to compare percentages for sociodemographic, lifestyle and dietary variables.
Data Collection Summary:

Timing of Measurements

When subjects were four and 43 years old. 

Dependent Variables

  • Variable One: Blood pressure measured twice at 43 years, after 45 minutes of sitting without smoking; second measure was used. Hypertension defined as at least 140/90mmHg or if the subject was taking medication for hypertension
  • Variable Two: Waist circumference measured twice at 43 years and the average used; measured at the mid-point between the costal margin and iliac crest to nearest 0.1cm. Large circumference indicated CVD risk, defined as more than 102cm in men and more than 88cm in women.

Independent Variables

  • Variable One: Energy-adjusted tertiles of vitamin E (mg per MJ) intake, calulated at ages four and 43
  • Variable Two: Occupational social class, measured as father's occupation type at age four and the subject's occupation type at 43
  • Variable Three: Region of residency at age 43, defined as Scotland, North, Central and London
  • Variable Four: Smoking at 43, either yes or no
  • Variable Five: Physical activity at age 43; active were those who took part in any sports, exercise or vigorous leisure activities at least once per week; others were considered inactive
  • Variable Six: Body weight and height at age 43, measured by nurse and used to calculate BMI
  • Variable Seven: Energy adjusted intake of vitamin C, beta-carotene at ages four and 43
  • Variable Eight: PUFA intake index at age 43, derived from intake of fat spreads consumed
  • Variable Nine: Dietary intake of calcium, sodium, potassium and magnesium at ages four and 43
  • Variable 10: Adult fruit and vegetable intake.
Description of Actual Data Sample:

 

Initial N: 5,362 in original birth cohort, 3,262 of the original were interviewed at age 43

Attrition (final N): 2,980 (1,484 males, 1,496 females); determined by those interviewed at both time points with dietary records

Age: Four 43 years old

Ethnicity: Native-born English, Scottish and Welsh

Other Relevant Demographics

Father's occupational social class in 1950 (age four):

  • Non-manual: 40.6%
  • Manual: 55.7%
  • Not recorded: 3.7%.

Subject's occupational social class in 1989 (age 43):

  • Non-manual: 63.2%
  • Manual: 30.6%
  • Not recorded: 6.2%.

Anthropometrics

Waist circumference and BMI included in results; data not included for first time point (age four).

Location

England, Scotland and Wales.

Summary of Results:
  • Groups of Vitamin E intake are indicated by the six groups: Childhood-high, adulthood-high (ChAh); childhood-low, adulthood-high (ClAh); childhood-high, adulthood-middle (ChAm); childhood-low, adulthood-middle (ClAm); childhood-high, adulthood-low (ChAl); childhood-low, adulthood-low (ClAl)
  • Odds ratios with 95% CI are given. A reference of 1.00 is used as the value for the ChAh group. A P-value is given for those values statistically different from the reference indicated in bold. Odds ratios were adjusted for all independent variables listed above. 

Variables

ChAh

ClAh

ChAm

ClAm

ChAl

ClAl

Statistical Significance

Hypertension

1.00

1.66
(0.98-2.80)

1.53
(0.84-2.81)

1.50
(0.87-2.59)

1.57
(0.84-2.93

1.78

(1.03-3.08)

P<0.05

Waist Circumference

1.00

1.06
(0.69-1.62)

1.21
(0.75-1.96)

1.15
(0.75-1.78)

0.68
(0.39-1.20

1.58 (1.02-2.43)

P<0.05

Dietary Vitamin E Intakes of Each Group in Childhood and Adulthood

Vitamin E Intake (mg per Day)

ClAl

ChAl

ClAm

ChAm

ClAh

ChAh

Childhood

2.2

3.2

2.2

3.2

2.2

3.2

Adulthood

5.3

5.1

8.5

8.2

14.2

13.1

Other significant results include: 

  • 12% of the subjects were hypertensive at age 43
  • 17% of subjects had a high waist circumference at age 43
  • All of the groups of Vitamin E intake (listed above) had a higher risk of being hypertensive, compared to the reference group of childhood-high, adulthood-high (ChAh), but they failed to reach statistical significance with the exception of the childhood-low, adulthood-low (ClAl) group that was different, P<0.05
  • The risk of hypertension was greater if father's and subject's social class was manual: 1.75 (1.23-2.47), compared to the reference of non-manual father and non-manual subject class
  • Risk of hypertension increased with BMI, 1.09 (1.06-1.13)
  • Risk of hypertension decreased with physical activity, 0.70 (0.54-0.93)
  • Men were more likely to be hypertensive than women: 1.71 (1.29-2.26)
  • There was no difference between the Vitamin E intake groups listed above regarding waist circumference, with the exception of the ClAl group that was 1.58 times more likely to have a high waist circumference
  • Those with a manual social class at age four were more likely to have a high waist circumference: 1.45 (1.09-1.93) and 1.75 (1.29-2.36)
  • Those who were physically active were 40% less likely to have a high waist circumference, compared to those who were not active.

 

Author Conclusion:
  • Low dietary Vitamin E intake in childhood (age four) and adulthood (age 43) is independently associated with hypertension and waist circumference, two-risk factors for CVD
  • The authors feel the conclusion is robust because it is independent of other variables including smoking, physical activity, occupational social class, intakes of fat, antioxidant vitamins, PUFAs and fruit and vegetables.
Funding Source:
University/Hospital: MRC Human Nutrition Research, Elsie Widdowson Laboratory (Cambridge University UK), University College and Royal Free Medical School
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:
  • Assessment of vitamin E intake with accuracy is difficult, due to lack of knowledge of amounts and types of fats consumed and the natural variation in foods. However, vitamin E content of fats and oils was used at the time, 1950 and 1989. A differential PUFA index of intake at age 43 was derived by categorizing the types of fat consumed into four groups.
  • Intake of vitamin supplements was not recorded and cod liver oil was distributed free of charge in 1950 to welfare subjects in this population. Baseline nutrition adequacy was not measured nor was cardiovascular health.
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) Yes
 
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? ???
  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? 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
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  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? ???
  4.1. Were follow-up methods described and the same for all groups? 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%.) ???
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. 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? ???
  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.) ???
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? ???
  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? 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
  6.4. 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? No
  6.6. Were extra or unplanned treatments described? No
  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
7. Were outcomes clearly defined and the measurements valid and reliable? N/A
  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? No
  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)? 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? 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? N/A
  10.2. Was the study free from apparent conflict of interest? N/A