Racial differences in AMD
Monday, January 16, 2012
Racial minorities, including Latinos and Asian Americans, do not appear to have similar risks of developing nonexudative and exudative Age-related macular degeneration (AMD) as whites in the United States, according to a recent study.
Several large population-based studies have examined differences in the prevalence of AMD between whites and blacks in the United States (Table). These studies have consistently demonstrated that AMD affects whites more than blacks. When examining differences in prevalence of AMD between other racial minorities and whites, there are conflicting findings as to whether Latinos have higher or lower rates of AMD relative to whites. An analysis of data from the National Health and Nutrition Examination Survey (NHANES) and another from the Multi-ethnic Study of Atherosclerosis (MESA) study found that Latinos had lower rates of early and late nonexudative AMD relative to whites. In contrast, findings from the Colorado-Wisconsin Study of Age-related Maculopathy showed higher rates of nonexudative AMD in Latinos compared with whites and the Proyecto VER identified signs of early AMD in over one quarter of Latinos over 50 years of age. While studies have assessed rates of AMD among individuals residing in Asian countries, little is known about the prevalence of AMD among Asian Americans. Given that Latino and Asian Americans constitute the 2 fastest-growing minorities in the United States,12 representing nearly 20% of the population, it is becoming increasingly important to have an improved understanding of the epidemiology of AMD for these groups.
Methods & Results
In this retrospective longitudinal cohort study billing records of all encounters for 2 259 061 beneficiaries aged ≥40 enrolled in a large, national US managed care network from 2001 through 2007 were reviewed and the incidence and prevalence of nonexudative and exudative AMD were determined and stratified by race. Cox regression analyses determined the hazard of nonexudative and exudative AMD for each race, with adjustment for confounders.
During the study, 113,234 individuals (5.0%) were diagnosed with nonexudative and 17,181 (0.76%) with exudative AMD. After adjustment for confounders, blacks had a significantly reduced hazard of nonexudative (hazard ratio [HR]=0.75, 95% confidence interval [CI]: 0.71-0.79) and exudative AMD (HR=0.70, 95% CI: 0.59-0.83) at age 60 and a reduced hazard of nonexudative (HR=0.56, 95% CI: 0.52-0.60) and exudative AMD (HR=0.45, 95% CI: 0.37-0.54) at age 80 relative to whites. Similar comparisons for Latinos demonstrated an 18% reduced hazard for nonexudative AMD at age 80 (HR=0.82, 95% CI: 0.76-0.88) relative to whites. Asian Americans showed a 28% increased hazard for nonexudative AMD at age 60 (HR=1.28, 95% CI: 1.20-1.36) but a 46% decreased hazard for exudative AMD at age 80 (HR=0.54, 95% CI: 0.40-0.73).
Discussion & Conclusions
In this large national study, we followed a cohort of individuals of each of the 4 major races longitudinally over time to assess for differences among the races in the hazard of developing nonexudative and exudative AMD. After adjustment for a number of key confounding factors in the multivariable regression analysis, we identified several important differences in the rates of developing AMD among the races. Our analysis confirms the findings of many other studies, demonstrating significantly lower rates of nonexudative and exudative AMD at ages 60 and 80 in blacks relative to whites. No differences were noted in rates of nonexudative AMD between Latinos and whites at age 60; however, by age 80 the hazard of developing nonexudative AMD was lower in Latinos relative to whites. In contrast, Latinos exhibited higher rates of exudative AMD relative to whites at age 60, though this difference became insignificant by age 80. The only group found to have an increased hazard of nonexudative AMD relative to whites were 60-year-old Asian Americans, though by age 80 no significant differences were noted between these 2 races. Below are comparisons among the findings from the present analysis with other published studies in the literature.
Blacks
Several large population-based studies, including the Atherosclerosis Risk in Communities Study, the MESA study, and the Salisbury Eye Evaluation Project, have reported decreased risk of early (nonexudative) AMD among blacks as compared with whites. Other population-based studies (the Baltimore Eye Survey and NHANES III) also showed less early AMD in blacks relative to whites, though the findings of these studies did not reach statistical significance. Our analysis confirmed the findings of these population-based studies, demonstrating a 25% decreased hazard of developing nonexudative AMD for blacks at age 60 (P < .0001) and a 44% decreased hazard of nonexudative AMD at age 80 (P < .0001) when compared to similar-aged whites.
While several studies describe reduced rates of exudative AMD among blacks relative to whites, only 2 studies have been able to show a statistically significant difference between the 2 races. All of the existing population-based studies that have attempted to compare rates of exudative AMD between blacks and whites have been limited by small numbers of blacks with exudative AMD (ranging from only 0 to 7 individuals in each study). As many of these studies have acknowledged, they were under-powered to detect a true difference in the rate of exudative AMD between the 2 races. The present analysis had adequate numbers of blacks (366 persons) and whites (12,857 persons) with exudative AMD to make comparisons among the groups. Our results corroborate the findings of a study by Javitt and associates, who performed a similar analysis by using Medicare claims data and showed significantly lower rates of exudative AMD in blacks relative to whites.
Latinos
The prevalence of nonexudative AMD in Latinos (3.81%) in our study was similar to that reported in the MESA study (4.0%), but considerably lower than 3 other population-based studies (7.0%-27.9%). The majority of participants in the latter 3 studies were of Mexican-American ancestry. According to the US Census Bureau, one-third of all Latinos residing in the United States originated from Latin American countries other than Mexico. Therefore, the rates of AMD generated from these 3 population-based studies may not be fully reflective of all Latinos residing in the United States.
In this study we found that Latinos at age 60 had a similar hazard of developing nonexudative AMD relative to whites, but had an 18% decreased hazard by age 80 (P < .0001). Three previous studies that compared early AMD in whites vs Latinos found no significant differences between these groups, but did not stratify the results by age, making direct comparisons difficult. Our analyses also demonstrated that Latinos had a significantly increased hazard for exudative AMD at age 60 relative to whites (P < .0001), which is contrary to what has been previously reported, though at age 80 this hazard was no longer significantly different for Latinos compared to whites (P = .17).
Asian Americans
While several papers have reported the prevalence of AMD among Asians residing in China, Japan, and other Asian countries, we are aware of only 1 population-based study that examined rates of AMD among Asian Americans (specifically, Chinese Americans) residing in the United States. In the present analysis, Asian Americans had a 28% increased hazard for developing nonexudative AMD at age 60, but this difference was no longer significant at age 80 relative to whites. Similar hazards were found when comparing 60-year-old Asian Americans to whites for exudative AMD, but the hazard was found to be significantly decreased for 80-year-old Asian Americans. Our findings differ from those of the MESA study, which showed a similar rate of early AMD for Chinese Americans compared to whites (OR: 0.74, CI: 0.48-1.15) but a significantly higher risk for exudative AMD (age- and sex-adjusted OR: 4.30, CI: 1.30-14.27).10 Reasons for these differences may include study design, particularly the fact that our analysis included Asians of many ethnicities, not just of Chinese ancestry, which was the predominant Asian ethnicity represented in MESA.
Recently, Kawasaki and associates performed a meta-analysis of data from 4 large population-based studies conducted in Asia along with Chinese Americans from the MESA study. These researchers found that Asians aged 40 to 79 had a prevalence rate of 6.8% for early AMD and 0.56% for late AMD. Despite major differences in study design between these population-based studies included in the meta-analysis and the methods we used, the prevalence estimates for early and late AMD are remarkably similar among the 2 studies.
Implications
One factor that may account for some of the differences in risk of exudative AMD among the races is tobacco use, a known risk factor for exudative AMD. A recent study by the Kaiser Family Foundation compared smoking rates among races within the United States and showed that both Latinos and Asians were less likely to smoke than whites. It is possible that the higher hazards of exudative AMD observed among whites in this study relative to other races may be attributable, in part, to greater tobacco use in persons of this race. A similar finding has been observed in the Hisayama and Funagata studies. When comparing rates of exudative AMD in Japanese male and female subjects, these studies report higher exudative AMD rates among male subjects, which may be attributable to greater tobacco use among Japanese males. Unfortunately, our data source does not contain information on smoking, so we were not able to explore how tobacco use may affect our study findings.
The proportion of the US population who are Latino or Asian American is expected to rise to 33% by 2050, and will number over 135 million people. Understanding rates of AMD in these groups is imperative, so that clinicians can have better insight into who is most at risk for developing this disease and health policymakers can use this information to help guide decisions pertaining to healthcare resource allocation.
In summary, racial minorities, including Latinos and Asian Americans, do not appear to have similar risks of developing nonexudative and exudative AMD as whites. Additional studies using other sources should be conducted to determine the generalizability of this study's findings to other groups.
Source:
Am J Ophthalmol. 2011 Aug;152(2):273-282.e3
http://www.ncbi.nlm.nih.gov/pubmed/21696700
Several large population-based studies have examined differences in the prevalence of AMD between whites and blacks in the United States (Table). These studies have consistently demonstrated that AMD affects whites more than blacks. When examining differences in prevalence of AMD between other racial minorities and whites, there are conflicting findings as to whether Latinos have higher or lower rates of AMD relative to whites. An analysis of data from the National Health and Nutrition Examination Survey (NHANES) and another from the Multi-ethnic Study of Atherosclerosis (MESA) study found that Latinos had lower rates of early and late nonexudative AMD relative to whites. In contrast, findings from the Colorado-Wisconsin Study of Age-related Maculopathy showed higher rates of nonexudative AMD in Latinos compared with whites and the Proyecto VER identified signs of early AMD in over one quarter of Latinos over 50 years of age. While studies have assessed rates of AMD among individuals residing in Asian countries, little is known about the prevalence of AMD among Asian Americans. Given that Latino and Asian Americans constitute the 2 fastest-growing minorities in the United States,12 representing nearly 20% of the population, it is becoming increasingly important to have an improved understanding of the epidemiology of AMD for these groups.
Methods & Results
In this retrospective longitudinal cohort study billing records of all encounters for 2 259 061 beneficiaries aged ≥40 enrolled in a large, national US managed care network from 2001 through 2007 were reviewed and the incidence and prevalence of nonexudative and exudative AMD were determined and stratified by race. Cox regression analyses determined the hazard of nonexudative and exudative AMD for each race, with adjustment for confounders.
During the study, 113,234 individuals (5.0%) were diagnosed with nonexudative and 17,181 (0.76%) with exudative AMD. After adjustment for confounders, blacks had a significantly reduced hazard of nonexudative (hazard ratio [HR]=0.75, 95% confidence interval [CI]: 0.71-0.79) and exudative AMD (HR=0.70, 95% CI: 0.59-0.83) at age 60 and a reduced hazard of nonexudative (HR=0.56, 95% CI: 0.52-0.60) and exudative AMD (HR=0.45, 95% CI: 0.37-0.54) at age 80 relative to whites. Similar comparisons for Latinos demonstrated an 18% reduced hazard for nonexudative AMD at age 80 (HR=0.82, 95% CI: 0.76-0.88) relative to whites. Asian Americans showed a 28% increased hazard for nonexudative AMD at age 60 (HR=1.28, 95% CI: 1.20-1.36) but a 46% decreased hazard for exudative AMD at age 80 (HR=0.54, 95% CI: 0.40-0.73).
Discussion & Conclusions
In this large national study, we followed a cohort of individuals of each of the 4 major races longitudinally over time to assess for differences among the races in the hazard of developing nonexudative and exudative AMD. After adjustment for a number of key confounding factors in the multivariable regression analysis, we identified several important differences in the rates of developing AMD among the races. Our analysis confirms the findings of many other studies, demonstrating significantly lower rates of nonexudative and exudative AMD at ages 60 and 80 in blacks relative to whites. No differences were noted in rates of nonexudative AMD between Latinos and whites at age 60; however, by age 80 the hazard of developing nonexudative AMD was lower in Latinos relative to whites. In contrast, Latinos exhibited higher rates of exudative AMD relative to whites at age 60, though this difference became insignificant by age 80. The only group found to have an increased hazard of nonexudative AMD relative to whites were 60-year-old Asian Americans, though by age 80 no significant differences were noted between these 2 races. Below are comparisons among the findings from the present analysis with other published studies in the literature.
Blacks
Several large population-based studies, including the Atherosclerosis Risk in Communities Study, the MESA study, and the Salisbury Eye Evaluation Project, have reported decreased risk of early (nonexudative) AMD among blacks as compared with whites. Other population-based studies (the Baltimore Eye Survey and NHANES III) also showed less early AMD in blacks relative to whites, though the findings of these studies did not reach statistical significance. Our analysis confirmed the findings of these population-based studies, demonstrating a 25% decreased hazard of developing nonexudative AMD for blacks at age 60 (P < .0001) and a 44% decreased hazard of nonexudative AMD at age 80 (P < .0001) when compared to similar-aged whites.
While several studies describe reduced rates of exudative AMD among blacks relative to whites, only 2 studies have been able to show a statistically significant difference between the 2 races. All of the existing population-based studies that have attempted to compare rates of exudative AMD between blacks and whites have been limited by small numbers of blacks with exudative AMD (ranging from only 0 to 7 individuals in each study). As many of these studies have acknowledged, they were under-powered to detect a true difference in the rate of exudative AMD between the 2 races. The present analysis had adequate numbers of blacks (366 persons) and whites (12,857 persons) with exudative AMD to make comparisons among the groups. Our results corroborate the findings of a study by Javitt and associates, who performed a similar analysis by using Medicare claims data and showed significantly lower rates of exudative AMD in blacks relative to whites.
Latinos
The prevalence of nonexudative AMD in Latinos (3.81%) in our study was similar to that reported in the MESA study (4.0%), but considerably lower than 3 other population-based studies (7.0%-27.9%). The majority of participants in the latter 3 studies were of Mexican-American ancestry. According to the US Census Bureau, one-third of all Latinos residing in the United States originated from Latin American countries other than Mexico. Therefore, the rates of AMD generated from these 3 population-based studies may not be fully reflective of all Latinos residing in the United States.In this study we found that Latinos at age 60 had a similar hazard of developing nonexudative AMD relative to whites, but had an 18% decreased hazard by age 80 (P < .0001). Three previous studies that compared early AMD in whites vs Latinos found no significant differences between these groups, but did not stratify the results by age, making direct comparisons difficult. Our analyses also demonstrated that Latinos had a significantly increased hazard for exudative AMD at age 60 relative to whites (P < .0001), which is contrary to what has been previously reported, though at age 80 this hazard was no longer significantly different for Latinos compared to whites (P = .17).
Asian Americans
While several papers have reported the prevalence of AMD among Asians residing in China, Japan, and other Asian countries, we are aware of only 1 population-based study that examined rates of AMD among Asian Americans (specifically, Chinese Americans) residing in the United States. In the present analysis, Asian Americans had a 28% increased hazard for developing nonexudative AMD at age 60, but this difference was no longer significant at age 80 relative to whites. Similar hazards were found when comparing 60-year-old Asian Americans to whites for exudative AMD, but the hazard was found to be significantly decreased for 80-year-old Asian Americans. Our findings differ from those of the MESA study, which showed a similar rate of early AMD for Chinese Americans compared to whites (OR: 0.74, CI: 0.48-1.15) but a significantly higher risk for exudative AMD (age- and sex-adjusted OR: 4.30, CI: 1.30-14.27).10 Reasons for these differences may include study design, particularly the fact that our analysis included Asians of many ethnicities, not just of Chinese ancestry, which was the predominant Asian ethnicity represented in MESA.
Recently, Kawasaki and associates performed a meta-analysis of data from 4 large population-based studies conducted in Asia along with Chinese Americans from the MESA study. These researchers found that Asians aged 40 to 79 had a prevalence rate of 6.8% for early AMD and 0.56% for late AMD. Despite major differences in study design between these population-based studies included in the meta-analysis and the methods we used, the prevalence estimates for early and late AMD are remarkably similar among the 2 studies.
Implications
One factor that may account for some of the differences in risk of exudative AMD among the races is tobacco use, a known risk factor for exudative AMD. A recent study by the Kaiser Family Foundation compared smoking rates among races within the United States and showed that both Latinos and Asians were less likely to smoke than whites. It is possible that the higher hazards of exudative AMD observed among whites in this study relative to other races may be attributable, in part, to greater tobacco use in persons of this race. A similar finding has been observed in the Hisayama and Funagata studies. When comparing rates of exudative AMD in Japanese male and female subjects, these studies report higher exudative AMD rates among male subjects, which may be attributable to greater tobacco use among Japanese males. Unfortunately, our data source does not contain information on smoking, so we were not able to explore how tobacco use may affect our study findings.
The proportion of the US population who are Latino or Asian American is expected to rise to 33% by 2050, and will number over 135 million people. Understanding rates of AMD in these groups is imperative, so that clinicians can have better insight into who is most at risk for developing this disease and health policymakers can use this information to help guide decisions pertaining to healthcare resource allocation.
In summary, racial minorities, including Latinos and Asian Americans, do not appear to have similar risks of developing nonexudative and exudative AMD as whites. Additional studies using other sources should be conducted to determine the generalizability of this study's findings to other groups.
Source:
Am J Ophthalmol. 2011 Aug;152(2):273-282.e3
http://www.ncbi.nlm.nih.gov/pubmed/21696700