MyVisionTest News Archive
Nov 16, 2009
High omega-6 fatty acid intake increases risk of AMD
A new epidemiologic study finds that diets high in omega-6 polyunsaturated fatty acids (PUFAs) were associated with increased risk of age-related macular degeneration (AMD), and may mask the protective influences of consuming diets high in omega-3 PUFAs (fish oil).
Previous epidemiological studies generally indicate a higher prevalence or progression of AMD among people with diets high in total fat, although associations are not always statistically significant. However, the associations with individual types of fats have been less consistent, with the exception of long-chain omega-3 polyunsaturated fatty acid (PUFA) or fish intake, which was generally related to decreased risk of AMD. Previous studies that examined the associations of saturated fatty acid (SFA), PUFA, and monounsaturated fatty acid (MUFA) intakes with AMD observed an increased risk (not always statistically significant) for the highest vs lowest levels of intake of these fats. Although all previous studies addressed advanced AMD, few studies addressed earlier stages that were detectable photographically, and in only 1 of these studies was diet assessed before photographic ascertainment of AMD.
Methods and Results
Women aged 50 to 79 years with high and low lutein intake from 3 sites of the Women's Health Initiative Observational Study were recruited into the Carotenoids in Age-Related Eye Disease Study. Fat intake from 1994 through 1998 was estimated using food frequency questionnaires, and AMD was assessed photographically from 2001 through 2004.
Intakes of omega-6 and omega-3 polyunsaturated fatty acids, which were highly correlated (r = 0.8), were associated with approximately 2-fold higher prevalence of intermediate AMD in high vs low quintiles. However, monounsaturated fatty acid intake was associated with lower prevalence. Age interactions were often observed. In women younger than 75 years (n = 1325), total fat and saturated fatty acid intakes were associated with increased prevalence of AMD (multivariate adjusted odds ratios for intermediate AMD, 1.7 for quintile 5 vs quintile 1 for total fat [P = .10 for trend] and 1.6 for saturated fatty acids [P = .23 for trend]). The associations were reversed in older women.
Previous investigations have observed a protective influence of omega-3 PUFA or fish to be stronger among people with lower intake of omega-6 PUFA, possibly because omega-6 PUFA replaces omega-3 PUFA in membranes and competes with omega-3 PUFA for cyclooxygenases to form proinflammatory eicosanoids. Therefore, the researchers computed associations of long-chain omega-3 PUFA intake with AMD separately, stratifying by intake level of omega-6 PUFA (above and below the median intake of 6% as a percentage of total energy). The adjusted ORs for AMD in the highest vs lowest quintile for long-chain omega-3 PUFA intake were 1.0 vs 2.7 for women below vs above the median for omega-6 PUFA intake (P = .38 for interaction).
Discussion and Conclusions
In this study, total fat intake was not associated with overall intermediate AMD; however, associations varied with age. Direct associations of total fat intake with AMD in the younger women (three-fourths of the sample) were consistent with the large body of evidence that suggests that AMD risk is directly associated with the level of total fat intake. High levels of fat intake have been significantly associated with higher prevalence, incidence, or progression in several studies. It is common knowledge that high-fat diets are often micronutrient poor. Consequently, high-fat diets might be a marker for diets that are poor in many micronutrients (vitamins, lutein, etc) that could protect against AMD.
The inverse associations between AMD and total fat intake in the older segment of the population (≥75 years) could be the result of selective mortality bias.
The intake of omega-6 PUFAs, primarily provided by added vegetable fats (salad dressing, mayonnaise, and margarine), was associated with an increased prevalence in intermediate AMD in the CAREDS sample. Similar associations with overall omega-6 PUFA intake or that of the major omegaa-6 PUFA (linoleic acid) have been observed in 5 previous investigations in American samples
These direct associations of omega-6 PUFA intake with AMD could reflect the fact that this is a common source of fat in this sample and that fat simply replaces calories spent on eating more nutrient-dense foods. It could also reflect a specific deleterious influence of these fats. Omega-6 PUFAs promote inflammation, which is thought to contribute to retinal damage that may promote AMD.
Another potential explanation for the direct association of omega-6 PUFAs with AMD in this study could be that solid vegetable fats — in America — are also a source of trans-fatty acids, which may be atherogenic. Trans-fatty acid intake in 3 American studies was associated with a high risk of AMD. However, in the present study, the intake of trans-fatty acids was not associated with AMD.
This study found a direct adverse association between AMD and the intake of omega-3 PUFAs. This is in contrast to protective associations between omega-3 PUFA or fish intake and AMD reported in numerous previous studies. This may be because omega-3 PUFA consumption was highly correlated with the omega-6 PUFA consumption in this study and to consuming both fat types concurrently. For example, a major source of omega-3 PUFA was tuna salad, which supplies not only long-chain omega-3 PUFAs but also high levels of omega-6 PUFAs in the form of mayonnaise.
A protective influence of omega-3 PUFAs may depend on the intake of omega-6 PUFAs. In 3 past studies in which omega-6 PUFAs were associated with higher risk, a protective association with long-chain omega-3 PUFA was observed only in conjunction with low levels of omega-6 PUFAs. In the present study, direct associations with omega-3 PUFA intake were stronger in women whose intake of omega-6 PUFAs was above — rather than below — 6% of energy, but the interaction was not statistically significant. Despite the results of the present study, the larger body of epidemiological evidence suggests that the intake of long-chain omega-3 PUFAs and/or fish is related to a lower risk of AMD.
The investigators state that their results support a growing body of evidence suggesting that diets high in several types of fat may contribute to the risk of intermediate AMD and that diets high in monounsaturated fatty acids may be protective.
Read more...
Arch Ophthalmol. 2009 Nov;127(11):1483-93
Tags: diet, fish, AMD, fat
A new epidemiologic study finds that diets high in omega-6 polyunsaturated fatty acids (PUFAs) were associated with increased risk of age-related macular degeneration (AMD), and may mask the protective influences of consuming diets high in omega-3 PUFAs (fish oil). Previous epidemiological studies generally indicate a higher prevalence or progression of AMD among people with diets high in total fat, although associations are not always statistically significant. However, the associations with individual types of fats have been less consistent, with the exception of long-chain omega-3 polyunsaturated fatty acid (PUFA) or fish intake, which was generally related to decreased risk of AMD. Previous studies that examined the associations of saturated fatty acid (SFA), PUFA, and monounsaturated fatty acid (MUFA) intakes with AMD observed an increased risk (not always statistically significant) for the highest vs lowest levels of intake of these fats. Although all previous studies addressed advanced AMD, few studies addressed earlier stages that were detectable photographically, and in only 1 of these studies was diet assessed before photographic ascertainment of AMD.
Women aged 50 to 79 years with high and low lutein intake from 3 sites of the Women's Health Initiative Observational Study were recruited into the Carotenoids in Age-Related Eye Disease Study. Fat intake from 1994 through 1998 was estimated using food frequency questionnaires, and AMD was assessed photographically from 2001 through 2004.
Intakes of omega-6 and omega-3 polyunsaturated fatty acids, which were highly correlated (r = 0.8), were associated with approximately 2-fold higher prevalence of intermediate AMD in high vs low quintiles. However, monounsaturated fatty acid intake was associated with lower prevalence. Age interactions were often observed. In women younger than 75 years (n = 1325), total fat and saturated fatty acid intakes were associated with increased prevalence of AMD (multivariate adjusted odds ratios for intermediate AMD, 1.7 for quintile 5 vs quintile 1 for total fat [P = .10 for trend] and 1.6 for saturated fatty acids [P = .23 for trend]). The associations were reversed in older women.
Previous investigations have observed a protective influence of omega-3 PUFA or fish to be stronger among people with lower intake of omega-6 PUFA, possibly because omega-6 PUFA replaces omega-3 PUFA in membranes and competes with omega-3 PUFA for cyclooxygenases to form proinflammatory eicosanoids. Therefore, the researchers computed associations of long-chain omega-3 PUFA intake with AMD separately, stratifying by intake level of omega-6 PUFA (above and below the median intake of 6% as a percentage of total energy). The adjusted ORs for AMD in the highest vs lowest quintile for long-chain omega-3 PUFA intake were 1.0 vs 2.7 for women below vs above the median for omega-6 PUFA intake (P = .38 for interaction).
Discussion and Conclusions
In this study, total fat intake was not associated with overall intermediate AMD; however, associations varied with age. Direct associations of total fat intake with AMD in the younger women (three-fourths of the sample) were consistent with the large body of evidence that suggests that AMD risk is directly associated with the level of total fat intake. High levels of fat intake have been significantly associated with higher prevalence, incidence, or progression in several studies. It is common knowledge that high-fat diets are often micronutrient poor. Consequently, high-fat diets might be a marker for diets that are poor in many micronutrients (vitamins, lutein, etc) that could protect against AMD.
The inverse associations between AMD and total fat intake in the older segment of the population (≥75 years) could be the result of selective mortality bias.
The intake of omega-6 PUFAs, primarily provided by added vegetable fats (salad dressing, mayonnaise, and margarine), was associated with an increased prevalence in intermediate AMD in the CAREDS sample. Similar associations with overall omega-6 PUFA intake or that of the major omegaa-6 PUFA (linoleic acid) have been observed in 5 previous investigations in American samples
These direct associations of omega-6 PUFA intake with AMD could reflect the fact that this is a common source of fat in this sample and that fat simply replaces calories spent on eating more nutrient-dense foods. It could also reflect a specific deleterious influence of these fats. Omega-6 PUFAs promote inflammation, which is thought to contribute to retinal damage that may promote AMD.
Another potential explanation for the direct association of omega-6 PUFAs with AMD in this study could be that solid vegetable fats — in America — are also a source of trans-fatty acids, which may be atherogenic. Trans-fatty acid intake in 3 American studies was associated with a high risk of AMD. However, in the present study, the intake of trans-fatty acids was not associated with AMD.
This study found a direct adverse association between AMD and the intake of omega-3 PUFAs. This is in contrast to protective associations between omega-3 PUFA or fish intake and AMD reported in numerous previous studies. This may be because omega-3 PUFA consumption was highly correlated with the omega-6 PUFA consumption in this study and to consuming both fat types concurrently. For example, a major source of omega-3 PUFA was tuna salad, which supplies not only long-chain omega-3 PUFAs but also high levels of omega-6 PUFAs in the form of mayonnaise.
A protective influence of omega-3 PUFAs may depend on the intake of omega-6 PUFAs. In 3 past studies in which omega-6 PUFAs were associated with higher risk, a protective association with long-chain omega-3 PUFA was observed only in conjunction with low levels of omega-6 PUFAs. In the present study, direct associations with omega-3 PUFA intake were stronger in women whose intake of omega-6 PUFAs was above — rather than below — 6% of energy, but the interaction was not statistically significant. Despite the results of the present study, the larger body of epidemiological evidence suggests that the intake of long-chain omega-3 PUFAs and/or fish is related to a lower risk of AMD.
The investigators state that their results support a growing body of evidence suggesting that diets high in several types of fat may contribute to the risk of intermediate AMD and that diets high in monounsaturated fatty acids may be protective.
Read more...
Arch Ophthalmol. 2009 Nov;127(11):1483-93
