EAL

FNOA: Antioxidants (2011-2012)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To examine the incidence of age-related macular degeneration (AMD) in a trial of combined folic acid, pyridoxine hydrochloride (vitamin B₆) and cyanocobalamin (vitamin B₁₂) therapy.

Inclusion Criteria:

Women from the ongoing Women's Antioxidant Cardiovascular Study (WACS), with pre-existing cardiovascular disease (CVD) or with three or more coronary risk factors.

Exclusion Criteria:

Women who reported a diagnosis of AMD on the baseline questionnaire were excluded.

Description of Study Protocol:

Recruitment

From August 1997 through January 1998, all 8,171 women participating in the WACS were sent invitations and consent forms for participation in the folic acid/pyridoxine/cyanocobalamin (combination treatment) arm of the trial.

Design

Randomized, double-blind, placebo-controlled trial.

Blinding Used

Double-blind study.

Intervention

Participants were randomly assigned to receive a combination of folic acid (2.5mg per day), pyridoxine hydrochloride (50mg per day) and cyanocobalamin (1mg per day) or placebo.

Statistical Analysis

Cox proportional hazards regression was used to estimate the relative risk (RR) of AMD among those assigned to receive the combination treatment compared with those assigned to receive the placebo after age adjustment (in years) at baseline and randomized assignments to ascorbic acid, vitamin E and beta carotene treatment
Models were also fit separately within the pre-specified age groups of 40 to 54 years, 55 to 64 years and 65 years or older
The proportionality assumption throughout the follow-up period was tested by including an interaction term of folic acid/pyridoxine/cyanocobalamin with the logarithm of time in the Cox models
For each RR, the 95% CI and two-sided P value were calculated.

Data Collection Summary:

Timing of Measurements

Women were randomized in April 1998 and the pill regimen was completed on July 31, 2005. Annual questionnaires were sent to all participants to monitor their adherence to the pill regimen and the occurrence of any relevant events including AMD.

Dependent Variables

Total AMD, defined as self-reported confirmed by a medical record evidence of an initial diagnosis after randomization but before July 31, 2005
Visually significant AMD with the same definition as total AMD but with best-corrected visual acuity loss to 20/30 or worse attributable to AMD.

Independent Variables

Treatment or placebo group.

Control Variables

Mean age: 40 to 54 years, 55 to 64 years, 65 years or older
Cigarette smoking: Current, past only, never
Alcohol use: Daily, weekly, rarely/never
BMI, mean (SD): less than 25%, 26% to 29.9%, 30% or more
Hypertension
Elevated cholesterol level
Diabetes mellitus
Prior cardiovascular disease
Menopausal Status: Pre-menopausal, post-menopausal/current HRT, post-menopausal/no HRT, dubious/unclear
Current use of multivitamin supplements
Aspirin use in the past month.

Description of Actual Data Sample:

Initial N: 5,205
Attrition (final N): At completion of the pill regimen, morbidity and mortality follow-up was 92.6% complete
Age:
- Combination group: 62.6 years (mean)
- Placebo group: 62.6 years (mean).

Other Relevant Demographics

Characteristic	Combination Group	Placebo Group
Cigarette smoking:
Current	11.4%	12.2%
Past only	43.6%	45.0%
Never	45%	42.7%
Alcohol use:
Daily	33.2%	32.7 %
Weekly	12.2%	12.4%
Rarely/never	54.6%	54.9%
Hypertension	86.6%	85.7%
Elevated cholesterol level	77.6%	78.8%
Diabetes mellitus	21.3%	21.6%
Prior cardiovascular disease	64.4%	62.6%
Menopausal status:
Pre-menopausal	6.3%	6.5%
Post-menopausal/current HRT	48.9%	49.3%
Post-menopausal/no HRT	42.3%	42.2%
Dubious/unclear	2.5%	2.0%
Current use of multivitamin supplement	22.5%	23.1%
Aspirin use in past month	62.4%	62.1%

Anthropometrics

Combination group: Mean BMI 30.6 (6.7)
Placebo group: Mean BMI 30.7 (6.7).

Location

Massachusetts, US.

Summary of Results:

During an average of 7.3 years of treatment and follow-up, a total of 137 cases of AMD were documented, including 70 cases of visually significant AMD:

Variables

Combination Group

Number of Cases

Placebo Group

Number of Cases

Statistical Analysis

Total AMD

RR 0.66, 95% CI: 0.47 to 0.93, (P=0.01)

Visually significant AMD

RR 0.59, 95% CI: 0.36 to 0.95, (P=0.03)

Relative risks did not vary significantly over the three age groups for either end point (P interactions, each more than 0.2)
A beneficial effect of the combination treatment on total AMD began to emerge at approximately two years of treatment and follow-up and persisted throughout the trial
For visually significant AMD, the curves appeared to diverge later in the trial at approximately four years
For both end points, the rate differences appeared to increase with longer follow-up:

	First Three years of Follow-up	Remaining 4.3 Years of Follow-up
Total AMD	RR 0.87, 95% CI: 0.54 to 1.42 (P=0.59)	RR .72, 95% CI: 0.44 to 1.18 (P=0.19)
Visually significant AMD	RR 0.84, 95% CI: 0.39 to 1.78 (P=0.65)	RR 0.52 95% CI: 0.27 to 0.98, (P=0.04)

There was not evidence that the effect of combination treatment on either AMD end point was modified by any AMD risk factor considered.

Author Conclusion:

Daily supplementation with folic acid, pyridoxine and cyanocobalamin during an average of 7.3 years of follow-up reduced the risk of AMD in women at increased risk of vascular disease
Those assigned to active treatment had a statistically significant 35% to 40% decreased risk of AMD. The beneficial effect of treatment began to emerge at approximately two years of follow-up and persisted throughout the trial.
Because there are currently no recognized means to prevent the early stages of AMD development other than avoidance of cigarette smoking, these findings could have important clinical and public health implications and need to be confirmed in other populations of men and women.

Funding Source:

Government:

National Heart, Lung, and Blood Institute and the National Eye Institute

Industry:

Cognis Corporation and BASF Corporation

Pharmaceutical/Dietary Supplement Company:

Reviewer Comments:

The authors note the following limitations:

Whether the reduced risk of AMD observed in WAFACS was due to lowering of homocysteine levels by the combination treatment or is independent of lowered homocysteine levels is an important question that needs further investigation
Sub-study findings indicate that the reduced risk of AMD in the combination group may have been due at least in part to lowering of homocysteine levels, but a treatment benefit independent of lowering homocysteine levels is also possible
Other plausible mechanisms include a direct antioxidant effect of folic acid and B vitamin supplements and enhancement of endothelial nitric oxide levels in the colloidal vasculature with an associated increase in vascular reactivity. Further study is required to distinguish between these and other possibilities
The findings from this study for AMD are in sharp contrast to the null findings for CVD observed in the WAFACS and other completed trials to lower homocysteine levels in persons with pre-existing vascular disease despite substantial lowering of homocysteine concentrations by study treatment in those trials
Although the findings could be due to chance and need to be confirmed in other populations, it may be worthwhile to consider whether the discordant findings for AMD and CVD reflect important differences between the choroidal and systemic vasculature with respect to responsiveness to the lowering of homocysteine levels. AMD is a small vessel disease that may be more amenable to benefit form lowering homocysteine concentrations and further study is necessary.

All enrolled subjects may not have been accounted for as only the point morbidity and mortality follow-up was provided for the end of the pill regimen.

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
	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?	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)	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.)	???
	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
	3.6.	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?		No
	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
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	No
	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?	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?	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
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?	N/A
	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?	Yes
	6.6.	Were extra or unplanned treatments described?	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
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)?	???
	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?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes