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Beta Carotene Supplementation and Age-Related Maculopathy in a Randomized Trial of US Physicians
William G. Christen, ScD;
JoAnn E. Manson, MD, DrPH;
Robert J. Glynn, ScD;
J. Michael Gaziano, MD;
Emily Y. Chew, MD;
Julie E. Buring, ScD;
Charles H. Hennekens, MD
Arch Ophthalmol. 2007;125(3):333-339.
ABSTRACT
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Objective To test whether beta carotene supplementation affects the incidence of age-related maculopathy (ARM) in a large-scale randomized trial.
Design Randomized, double-masked, placebo-controlled trial among 22 071 apparently healthy US male physicians aged 40 to 84 years. Participants were randomly assigned to receive beta carotene (50 mg every other day) or placebo.
Main Outcome Measure Incident ARM responsible for a reduction in best-corrected visual acuity to 20/30 or worse.
Results After 12 years of treatment and follow-up, there were 162 cases of ARM in the beta carotene group vs 170 cases in the placebo group (relative risk [RR], 0.96; 95% confidence interval [CI], 0.78-1.20). The results were similar for the secondary end points of ARM with or without vision loss (275 vs 274 cases; RR, 1.01; 95% CI, 0.86-1.20) and advanced ARM (63 vs 66 cases; RR, 0.97; 95% CI, 0.69-1.37).
Conclusions These randomized data relative to 12 years of treatment among a large population of apparently healthy men indicate that beta carotene supplementation has no beneficial or harmful effect on the incidence of ARM. Long-term supplemental use of beta carotene neither decreases nor increases the risk of ARM.
Trial Registration clinicaltrials.gov Identifier: NCT00000152
INTRODUCTION
In the United States, an estimated 30% of persons 65 years and older show signs of early age-related maculopathy (ARM) or its late-stage manifestations, which are also known as age-related macular degeneration (AMD).1-2 Despite its common occurrence, there are no generally available treatment options. Laser photocoagulation,3-4 photodynamic therapy,5-6 and antivascular endothelial growth factor therapy7-8 are effective only for persons with the late-stage neovascular form of the disease. Most affected individuals have the earlier atrophic form of ARM, which has no known proven treatment. For these reasons, identification of preventive measures is of particular clinical and public health importance.
In some observational studies,9-12 individuals who self-select for use of antioxidant nutrients and other dietary intakes have lower risk of ARM. Evidence from randomized trials is accumulating to evaluate a possible role for nutritional supplement use in delaying disease onset and progression. The Age-Related Eye Disease Study13 (AREDS) demonstrated that treatment with high-dose antioxidant supplements (ascorbic acid, vitamin E, and beta carotene) and zinc could mitigate the progression to advanced ARM in persons at high risk. These findings in the AREDS are an important advance in disease prevention and serve as the basis for current recommendations regarding nutritional supplement use in persons at high risk for ARM.14 Nonetheless, many important questions remain. Citing possible adverse effects of components in the AREDS formulation, some ophthalmologists suggest the use of alternative formulations,15 which remain largely unproved. The value of antioxidant supplement use in persons at usual risk for ARM was not evaluated in the AREDS and remains to be determined. Among persons at usual risk for ARM and at increased risk for advanced ARM, these and other unresolved issues of clinical importance can be addressed with further information on the effects of each component of the AREDS formulation and of other nutrient combinations.
Beta carotene was included in the AREDS13 formulation at the start of that trial because it was readily available in a research formulation and was already under investigation in large randomized trials of cancer and cardiovascular disease. One of these was the Physicians' Health Study I16 (PHS I), which tested beta carotene and low-dose aspirin use among 22 071 apparently healthy US male physicians. The main trial results for the PHS I showed no benefit or harm of 12 years' use of beta carotene treatment on cancer or cardiovascular disease end points. In this article, we describe the results for ARM from the randomized beta carotene component of the PHS I.
METHODS
STUDY POPULATION
The PHS I16 was a randomized, double-masked, placebo-controlled trial of the use of beta carotene (Lurotin) (50 mg every other day) and low-dose aspirin (Bufferin) (325 mg every other day) in the primary prevention of cardiovascular disease and cancer among 22 071 apparently healthy US male physicians aged 40 to 84 years in 1982. Information collected at baseline included height, weight, alcohol use, current multivitamin use, blood pressure, cholesterol level, physical activity, history of cigarette smoking, and history of diabetes mellitus. Participants completed annual follow-up questionnaires supplying information about their compliance with the treatment regimens and about the occurrence of any relevant events. Informed consent was obtained from all participants, and the research protocol was reviewed and approved by the institutional review board at Brigham and Women's Hospital.
The randomized aspirin component of the PHS I was terminated early on January 25, 1988, primarily because of a statistically significant (P<.001) 44% reduction in the risk of a first myocardial infarction in the aspirin group.17 The randomized beta carotene component continued uninterrupted until its scheduled termination on December 31, 1995, with a mean duration of treatment of 12 years (range, 11.6-14.2 years).16 At the end of 11 years of follow-up (the last year completed for all participants), 99.2% were still providing information on morbidity, and the follow-up for mortality was 99.9% complete. Eighty percent of participants in the beta carotene group and in the placebo group were still taking the study pills, with a mean compliance among pill takers of more than 97%. Therefore, even after 11 years, 78% of the study pills assigned in the beta carotene group were reported as still being taken. In the placebo group, 6% of participants reported taking supplemental beta carotene or vitamin A. The validity of reported compliance with the assigned treatment was assessed by measuring plasma beta carotene concentrations in specimens obtained at unannounced visits to a small sample of participants in 3 geographic areas. Those assigned to receive beta carotene had significantly higher mean concentrations than those assigned to receive placebo (1.2 vs 0.3 mg/L [2.24 vs 0.56 mmol/L], P<.001).18
ASCERTAINMENT AND DEFINITION OF END POINTS
Information on diagnoses of ARM made during the first 7 years of the trial was requested on the 84-month questionnaire. Physicians were asked, "Have you ever had macular degeneration diagnosed in your right (left) eye?" If they answered yes, they were requested to provide the month and year of the diagnosis. Subsequent annual questionnaires requested information on diagnoses during the preceding year. Signed permission to examine medical records pertaining to the diagnosis was requested on the questionnaires and, when necessary, in separate follow-up mailings. Ophthalmologists and optometrists were contacted by mail and were requested to complete an ARM questionnaire supplying information about the date of initial diagnosis, the best-corrected visual acuity at the time of diagnosis, and the date when the best-corrected visual acuity reached 20/30 or worse (if different from the date of initial diagnosis). Information was also requested about the signs of ARM observed (drusen, disciform scar, geographic atrophy, subretinal neovascular membrane, or retinal pigment epithelium [RPE] hypopigmentation, hyperpigmentation, or detachment) when visual acuity was first noted to be 20/30 or worse, as well as the date when exudative neovascular disease, if present, was first noted (defined by the presence of disciform scar, RPE detachment, or subretinal neovascular membrane). We also asked whether there were other ocular abnormalities that would explain or contribute to vision loss and, if so, whether the ARM by itself was enough to cause the best-corrected visual acuity to be reduced to 20/30 or worse. Medical records were obtained for more than 92% of participants reporting ARM.
The primary end point was visually significant ARM, defined as a self-report confirmed by medical record evidence of an initial diagnosis after randomization but before December 31, 1995, with a reduction in best-corrected visual acuity to 20/30 or worse attributable to ARM. The following 2 secondary end points were also defined: ARM with or without vision loss, composed of all incident cases, and advanced ARM, composed of cases of visually significant ARM with pathologic findings of disciform scar, RPE detachment, geographic atrophy, or subretinal neovascular membrane. The advanced ARM end point was defined to provide a more direct comparison of our results with the findings for advanced AMD in the AREDS.13
The present study includes 21 142 participants who were followed up for at least 7 years and who provided information on diagnoses of ARM made during the first 7 years of the trial on the 84-month questionnaire (ie, physicians who died during the first 7 years of follow-up were excluded). Of these, 10 585 were in the beta carotene group, and 10 557 were in the placebo group (eFigure).
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eFigure. Study design. Excluded were 929 participants who died during the first 7 years of the trial or who did not provide information about diagnoses of age-related maculopathy made during the first 7 years of the trial (requested on the 84-month questionnaire).
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DATA ANALYSIS
Cox proportional hazards regression models were used to estimate the relative risk (RR) of ARM among those assigned to beta carotene compared with those assigned to placebo after adjustment for age at baseline and for randomized aspirin treatment. Models were also fit separately within the following 4 age groups: 40 to 49, 50 to 59, 60 to 69, and 70 to 84 years. Tests for trend of the effect of age on any association between beta carotene use and ARM were calculated by including a term for the interaction of beta carotene supplementation and age (expressed as a continuous variable with values ranging from 1 to 4 corresponding to the 4 age groups) in a Cox proportional hazards regression model. For each RR, the 95% confidence interval (CI) and 2-sided P value were calculated. All analyses were conducted using SAS statistical software, version 8.2 (SAS Institute Inc, Cary, NC).
We also analyzed subgroup data according to baseline categories of alcohol use (daily, weekly, or rarely), cigarette smoking (never or past, or current), high cholesterol level (defined as  240 mg/dL [6.22 mmol/L] or past or current lipid-lowering treatment) (yes or no), current multivitamin use (yes or no), body mass index (calculated as weight in kilograms divided by the square of height in meters) (<25.0, 25.0-29.9, or 30.0), and the presence of hypertension (defined as reported systolic blood pressure of 140 mm Hg, diastolic blood pressure of 90 mm Hg, or history of treatment for high blood pressure) (yes or no to explore the possible modification of any effect of beta carotene supplementation). Tests of interaction were performed to evaluate the statistical significance of any modifying effect of these variables. We also used an interaction term that included the length of follow-up to test for a trend of the RR over time and to evaluate the adequacy of the Cox proportional hazards regression assumption over time.
Individuals, rather than eyes, were the unit of analysis because eyes were not examined independently, and participants were classified according to the status of the worse eye as defined by disease severity. When the worse eye was excluded because of vision loss attributed to other ocular abnormalities, the fellow eye was considered for classification.
RESULTS
Baseline characteristics of the beta carotene and placebo groups are given in Table 1. As expected in a large randomized trial, these characteristics were equally distributed between the 2 groups.
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Table 1. Baseline Characteristics of the Beta Carotene and Placebo Groups in Physicians’ Health Study I*
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During a mean of 12 years of treatment and follow-up, 549 cases of ARM were confirmed. These included 332 cases of visually significant ARM, approximately two thirds of which were characterized by a combination of drusen and RPE changes when visual acuity was first noted to be 20/30 or worse. One hundred twenty-nine participants with visually significant ARM developed signs of advanced ARM during the follow-up period.
There was no statistically significant benefit or harm of beta carotene supplementation relative to any end point (Table 2). For the primary end point of visually significant ARM, there were 162 cases in the beta carotene group vs 170 cases in the placebo group (RR, 0.96; 95% CI, 0.78-1.20). Similar findings were observed for the end points of ARM with or without vision loss and advanced ARM. For all 3 end points, the RRs did not vary significantly among the 4 age groups (interaction P>.7 for all).
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Table 2. Confirmed Cases of Age-Related Maculopathy (ARM)
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The Figure shows the cumulative incidence rates of visually significant ARM, ARM with or without vision loss, and advanced ARM according to the year of follow-up. There were no significant effects of beta carotene supplementation on any of the end points after excluding cases diagnosed during the first 2 years of follow-up (visually significant ARM: RR, 0.93; 95% CI, 0.74-1.16; ARM with or without vision loss: RR, 0.99; 95% CI, 0.83-1.17; and advanced ARM: RR, 0.95; 95% CI, 0.66-1.37) or during the first 5 years of follow-up (visually significant ARM: RR, 0.93; 95% CI, 0.73-1.19; ARM with or without vision loss: RR, 1.06; 95% CI, 0.88-1.27; and advanced ARM: RR, 0.84; 95% CI, 0.55-1.28). Tests of proportionality of the hazard ratios indicated no statistically significant trend over time for any end point (visually significant ARM, P = .16; ARM with or without vision loss, P = .99; and advanced ARM, P = .19).
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Figure. Cumulative incidence rates of age-related maculopathy (ARM).
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There was no evidence for any modification of the lack of effect of beta carotene supplementation on the incidence of ARM by the baseline categories of alcohol use, blood pressure, cholesterol level, body mass index, cigarette smoking, or current multivitamin use. The results of these analyses for the end point of visually significant ARM are given in Table 3.
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Table 3. Relative Risk (RR) of Visually Significant ARM as Modified by Other Risk Factors
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COMMENT
These randomized trial data of 12 years' duration from a large population of apparently healthy male physicians indicate that beta carotene treatment has no statistically significant beneficial or harmful effect on the risk of ARM. Men in the beta carotene group had a nonsignificant 4% lower risk of the primary study end point of visually significant ARM. The 95% CI around this estimate excluded a beneficial effect of 25% or greater or a harmful effect of 20% or greater. The RR estimates for the secondary end points of ARM with or without vision loss and advanced ARM were near the null value of 1.0.
Some potential limitations of the trial need to be considered, particularly in view of the null findings. It seems unlikely that an inadequate dosage of beta carotene explains the null findings. The dosage used in this study (50 mg every other day) increased the plasma beta carotene concentration approximately 4-fold18-19 (similar to the increase in beta carotene concentration observed in the AREDS13) and placed men in the beta carotene group in the top few percentiles of the general population with respect to usual intake. It also seems unlikely that the duration of treatment of 12 years was insufficient to materially reduce the risk of ARM. In the AREDS, the beneficial effect of high-dose antioxidant and zinc supplements was apparent after a treatment duration of 6.3 years, suggesting that the 12 years of treatment in the PHS I was sufficient to detect any possible benefit of beta carotene supplementation. Exclusion of cases diagnosed during the first 2 years or the first 5 years of follow-up had little effect on RR estimates, suggesting that there was no delayed effect for beta carotene supplementation. Poor compliance with the assigned treatment also seems an unlikely explanation for our findings. At the end of the trial, compliance was still 78% in the beta carotene group, and only 6% of participants in the placebo group reported taking beta carotene or vitamin A supplements. Other possible explanations for our findings include bias in the ascertainment of the end points and confounding by other factors. Because it was not feasible to perform ocular examinations on all participants, the ascertainment of ARM cases was based on participant reports; therefore, some degree of underascertainment of ARM is plausible. However, the underascertainment of disease is not associated with bias in randomized comparisons. Random misclassification of reported ARM, which would tend to shift the RR estimate toward the null, was reduced by the use of medical records to confirm the participant reports. Furthermore, the participants are all physicians. Nonrandom or differential misclassification was unlikely because medical records were reviewed without knowledge of beta carotene treatment assignment, and study participants and treating ophthalmologists and optometrists were unaware of beta carotene treatment assignment. Confounding is unlikely in this large randomized trial because, as expected, baseline characteristics were equally distributed between the beta carotene and placebo groups. This equal distribution of risk factors provides reassurance that other potential confounders that were unmeasured or were unknown were likely to be evenly distributed between the 2 groups.
Beta carotene supplementation in ARM has been examined in 2 previous randomized trials. In the Alpha-Tocopherol, Beta-Carotene Study,20 a randomized trial of alpha tocopherol (50 mg) and beta carotene (20 mg) daily supplementation that was conducted among more than 29 000 Finnish male smokers aged 50 to 69 years, end-of-trial eye examinations were performed for a subsample of 941 participants 65 years or older. Based on analysis of fundus photographs, 269 participants (28.6%) were judged to show signs of ARM at trial end, with most cases (239/269 [88.8%]) classified as dry maculopathy with hard drusen or pigmentary changes. In that trial, there was no beneficial effect of beta carotene supplementation on the prevalence of ARM (RR, 1.04; 95% CI, 0.74-1.47). The AREDS13 examined whether daily supplement use of zinc and an antioxidant combination of beta carotene (15 mg), ascorbic acid (500 mg), and vitamin E (400 IU) could delay progression to advanced AMD among 3640 participants aged 55 to 80 years at high risk for AMD. During a mean of 6.3 years of follow-up, 803 incident cases of advanced AMD were identified. Compared with individuals assigned to placebo, those assigned to zinc plus antioxidant supplements had a statistically significant 28% (RR, 0.72; 99% CI, 0.52-0.98) reduced risk of advanced AMD. Those assigned to antioxidant supplements alone had a somewhat smaller and statistically nonsignificant 20% (RR, 0.80; 99% CI, 0.59-1.09) reduced risk of advanced AMD. Because the antioxidant agents were tested in combination, the specific effects of beta carotene, ascorbic acid, and vitamin E could not be determined in the AREDS.
Our findings in the PHS I are in general agreement with the findings of the Alpha-Tocopherol, Beta-Carotene Study20 in suggesting that long-term supplementation with beta carotene has no marked beneficial or harmful effect on early stages of ARM development. A comparison of our findings with those of the AREDS13 is complicated by the absence of specific information on the effect of beta carotene in the AREDS formulation and by the testing of a higher-risk population and the use of an end point of more severe ARM in that trial. When we considered only the 129 cases of advanced ARM characterized by geographic atrophy or signs of exudative disease in our study, an end point more comparable with the end point of advanced AMD examined in the AREDS, we found no evidence of benefit or harm from the 12 years of beta carotene treatment (RR, 0.97; 95% CI, 0.69-1.37). However, the 95% CI around this estimate was wide, probably because of the smaller number of cases.
Initial enthusiasm for supplementation with beta carotene was tempered by the emergence of evidence in the mid-1990s that suggested that large dosages of beta carotene could be harmful in smokers.21-22 However, the main trial results for the PHS I indicated that 12 years of randomized beta carotene treatment had no beneficial or harmful effect on any cancer or cardiovascular disease end point in the overall population or in the 11.0% of physicians who were current smokers at baseline.16 Two other randomized trials also reported no effect of beta carotene supplementation on cancer, cardiovascular, or mortality end points.23-24
Concern about the possible adverse effects of beta carotene supplementation in smokers caused some ophthalmologists to recommend that smokers avoid taking beta carotene in the AREDS13 formulation and instead to recommend a supplement with only some of the trial ingredients.15 Several additional preparations of the original AREDS supplement are commercially available.15 However, the effect of removing 1 or more ingredients from the AREDS formulation cannot be predicted, and the effects on ARM of different combinations of antioxidant nutrients and other preventive agents will need to be tested in randomized trials. Our data, particularly as they apply to advanced ARM, suggest that the reduction in ARM progression observed for the antioxidant combination in the AREDS is unlikely to reflect an important independent beneficial effect for beta carotene supplementation and that removal of beta carotene from the AREDS formulation should have no material effect on the efficacy of the supplement. The observation that beta carotene is found only in trace amounts in the retina25-28 provides some indirect support for this suggestion. Nevertheless, a possible indirect effect of beta carotene in the AREDS formulation, mediated through interaction with other trial ingredients,29-31 cannot be excluded.
In summary, the results of this trial indicate that beta carotene supplementation for 12 years has little effect on the development of visually significant ARM in apparently healthy men. These findings, together with forthcoming data from other completed and ongoing trials,32-35 will complement the findings in the AREDS13 by clarifying the effects of individual antioxidant supplements and other nutrient combinations and should help ensure rational clinical and public health recommendations for the prevention of ARM.
AUTHOR INFORMATION
Correspondence: William G. Christen, ScD, Division of Preventive Medicine, Department of Medicine, Brigham and Women's Hospital, 900 Commonwealth Ave E, Boston, MA 02215-1204 (wchristen{at}rics.bwh.harvard.edu).
Submitted for Publication: May 18, 2006; final revision received September 25, 2006; accepted September 26, 2006.
Author Contributions: Dr Christen had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Financial Disclosure: Dr Christen has received research funding support from the National Institutes of Health (NIH), Harvard University (Clinical Nutrition Research Center), and DSM Nutritional Products, Inc (Roche). Dr Manson has received research funding support from the NIH and research support for study pills and/or packaging from BASF and Cognis. Dr Glynn has been funded from grants to the Brigham and Women's Hospital from Astra Zeneca, Bristol-Meyers Squibb Company, Merck and Co, Inc, and Novartis AG. Dr Gaziano has received support or honoraria from or has served as a consultant to BASF, Bayer AG, DMS Pharmaceuticals, McNeil Consumer Products, Pfizer Inc, PLIVA, and Wyeth Pharmaceuticals and has served as an expert witness for GlaxoSmithKline Inc, Merck and Co, Inc, and Nutra Quest International, Inc. Dr Buring has received investigator-initiated research funding and support from the NIH (National Heart, Lung, and Blood Institute, National Cancer Institute, and National Institute on Aging) and Dow Corning Corporation; research support for pills and/or packaging from Bayer Health Care and the National Source Vitamin E Association; honoraria from Bayer for speaking engagements; and serves on an external scientific advisory committee for a study by Procter & Gamble. Dr Hennekens has received support from or has served as a consultant to or on speakers bureaus for Actelion Ltd and Actelion Pharmaceuticals Ltd, Agatston Research Institute, Amgen Inc, AstraZeneca, Bayer AG, Bristol-Myers Squibb Company, Chattem, Inc, Delaco Company, the US Food and Drug Administration, GlaxoSmithKline Inc, Keryx Biopharmaceuticals, Inc, McNeil Consumer Products, Merck and Co, Inc, the National Institutes of Health, Novartis AG, Pfizer Inc, Reliant Pharmaceuticals, LLC, TAP Pharmaceutical Products Inc, United BioSource Corporation, and UpToDate and is a coinventor on patents held by Brigham and Women's Hospital.
Funding/Support: This study was supported by grants HL 26490, HL 34595, CA 34944, CA 40360, and EY 06633 from the National Institutes of Health (Dr Gaziano).
Additional Information: The online-only eFigure is available.
Acknowledgments: We acknowledge the crucial contributions of the entire staff of the PHS under the leadership of Charlene Belanger, MPH, Mary Breen, Vadim Bubes, PhD, Jean MacFadyen, Geneva McNair, David Potter, Leslie Power, Harriet Samuelson, MA, Miriam Schvartz, MD, Mickie Sheehey, Joanne Smith, and Phyllis Johnson Wojciechowski. We are also indebted to the 22 071 dedicated and committed participants of the PHS.
Author Affiliations: Division of Preventive Medicine, Department of Medicine, Brigham and Women's Hospital (Drs Christen, Manson, Glynn, Gaziano, and Buring), Departments of Epidemiology (Dr Manson) and Biostatistics (Dr Glynn), Harvard School of Public Health, and Department of Ambulatory Care and Prevention, Harvard Medical School (Dr Buring), Harvard University, and Massachusetts Veterans Epidemiology Research and Information Center, Department of Veterans Affairs Boston Healthcare System (Dr Gaziano), Boston; National Eye Institute, Bethesda, Md (Dr Chew); and Departments of Medicine and Epidemiology and Public Health, University of Miami School of Medicine, Miami, and Department of Biomedical Science, Center of Excellence in Biomedical and Marine Biotechnology, Florida Atlantic University, Boca Raton (Dr Hennekens).
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