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American Journal of Clinical Nutrition, Vol. 88, No. 1, 216-223, July 2008
© 2008 American Society for Nutrition

ORIGINAL RESEARCH COMMUNICATION

Blood concentrations of individual long-chain n–3 fatty acids and risk of nonfatal myocardial infarction1,2,3

Qi Sun, Jing Ma, Hannia Campos, Kathryn M Rexrode, Christine M Albert, Dariush Mozaffarian and Frank B Hu

1 From the Departments of Nutrition (QS, HC, and FBH) and Epidemiology (DM and FBH), Harvard School of Public Health, Boston, MA, and the Channing Laboratory (JM, DM, and FBH), the Division of Cardiovascular Medicine (CMA and DM), and the Division of Preventive Medicine (KMR and CMA), Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA

2 Supported by research grants CA49449, CA42182, HL24074, HL34594, and CA87969 from the National Institutes of Health, by a Postdoctoral Fellowship from the Unilever Corporate Research (to QS), and by an American Heart Association Established Investigator Award (to FBH).

3 Reprints not available. Address correspondence to FB Hu, Department of Nutrition, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115. E-mail: frank.hu{at}channing.harvard.edu.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Background: Whereas dietary intake of long-chain n–3 fatty acids has been associated with risk of nonfatal myocardial infarction (MI), few studies have examined the relation for blood concentrations.

Objective: We aimed to investigate the effect of long-chain n–3 fatty acids in blood on the risk of nonfatal MI.

Design: Baseline blood samples were collected from 32 826 participants of the Nurses' Health Study in 1989–1990, among whom 146 incident cases of nonfatal MI were ascertained during 6 y of follow-up and matched with 288 controls.

Results: After multivariate adjustment, the relative risks (95% CI) comparing the highest with the lowest quartiles in plasma were 0.23 (0.09, 0.55; P for trend = 0.001) for eicosapentaenoic acid (EPA), 0.40 (0.20, 0.82; P for trend = 0.004) for docosapentaenoic acid (DPA), and 0.46 (0.18, 1.16; P for trend = 0.07) for docosahexaenoic acid (DHA). The associations for these fatty acids in erythrocytes were generally weaker and nonsignificant. In contrast to EPA and DHA, blood concentrations of DPA were not correlated with dietary consumption of n–3 fatty acids. Higher plasma concentrations of EPA, DPA, and DHA were associated with higher plasma concentrations of HDL cholesterol and lower concentrations of triacylglycerol and inflammatory markers.

Conclusions: Higher plasma concentrations of EPA and DPA are associated with a lower risk of nonfatal MI among women. These findings may partly reflect dietary consumption but, particularly for DPA, may indicate important risk differences based on metabolism of long-chain n–3 fatty acids.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
An inverse association of fish intake with the risk of developing fatal coronary heart disease (CHD) or sudden cardiac death has been consistently observed in populations with low-to-moderate fish intake, compared with little or no intake (1-9). These findings are consistent with antiarrhythmic effects of long-chain n–3 fatty acids in experimental studies (10-12) and clinical trial evidence that supplementation of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (1 g/d), 2 major long-chain n–3 fatty acids, reduced coronary death—especially sudden cardiac death—among myocardial infarction (MI) survivors (13).

Compared with the literature on fatal CHD, less epidemiologic evidence exists regarding associations of consumption of fish or long-chain n–3 fatty acid intake with the risk of nonfatal MI (3-5, 14-16). In most prospective cohort studies conducted in Western countries, higher fish consumption or long-chain n–3 fatty acid intake either was not associated or was weakly associated with lower risk of nonfatal MI without significant trends (4, 5, 14-16). In a previous analysis in the Nurses' Health Study, we found that higher consumption of total long-chain n–3 fatty acids was significantly associated with a lower risk of both coronary death and nonfatal MI, although the association was stronger for coronary death (3). In 2 hospital-based retrospective case-control studies, whole blood or serum contents of EPA+DHA were associated with a lower risk of nonfatal coronary events (17, 18), but this association was not observed in the prospective Cardiovascular Health Study (14). Recently, among Japanese with background fish intake much higher than that in usual Western diets, a clinical trial showed that EPA supplementation significantly reduced the incidence of nonfatal CHD (19), and a cohort study also showed that very high levels of fish intake in Japan were significantly associated with a lower risk of nonfatal CHD (20).

To further investigate the relations of n–3 fatty acids with nonfatal MI, particularly of individual long-chain n–3 fatty acids in tissues that might be affected by both diet and metabolism, as well as precursors of these fatty acids, we examined the associations of EPA, docosapentaenoic acid (DPA), and DHA concentrations in plasma and in erythrocyte membranes with the risk of nonfatal MI in a nested case-control study.


   SUBJECTS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Study population and collection of blood samples
The Nurses' Health Study began in 1976 when 121 700 female registered nurses aged 30–55 y were enrolled and completed baseline questionnaires about their lifestyle and medical history. In 1989 and 1990, blood samples were received from 32 826 participants on request. The average age at blood draw was 60 y. Methods of blood sample collection and transportation were described in detail elsewhere (21). Most (97%) of the blood samples arrived within 26 h of phlebotomy. Immediately on arrival, the samples were centrifuged (1200 x g for 15 min at room temperature) and divided into aliquots of plasma, erythrocytes, and buffy coat fractions, which were then placed in liquid nitrogen freezers at ≤–130 °C until analysis.

The current case-control study was conducted among the nurses who provided blood samples and were free of diagnosed cancer or cardiovascular disease at the time of phlebotomy. During 6 y of follow-up, we documented 147 nonfatal MI and 20 fatal CHD. For each case, 2 controls were randomly selected by risk-set sampling and were matched to the case for age (±1 y), smoking status (never, past, or current), and fasting status (fasting for 8 h or not). In the current study, we excluded fatal CHD because of the small numbers and likely different mechanisms for the reduction in fatal events for n–3 fatty acids. After exclusion of the participants with missing fatty acid data, 146 nonfatal MI cases and 288 controls were available for the present analysis.

All participants gave written informed consent. The study protocol was approved by the Institutional Review Board of the Brigham and Women's Hospital and by the Human Subjects Committee Review Board of the Harvard School of Public Health.

Ascertainment of coronary heart disease
Participants reporting cardiovascular endpoints on biennial questionnaires were asked for their medical records to confirm endpoints. Study physicians who were blinded to the exposure status of participants reviewed available medical records to confirm nonfatal MI by using World Health Organization criteria (22), which require typical symptoms plus either diagnostic electrocardiographic findings or elevated cardiac enzyme concentrations. For those whose medical records were unavailable, the diagnosis was considered probable if supported by telephone interview or other supplemental information. Of 146 nonfatal MI cases, 143 (97.9%) were confirmed by medical records, and 3 (2.1%) were confirmed by telephone interview.

Laboratory procedures
We shipped each case-control triplet to the lab in the same batch and assayed the samples in a random sequence under identical conditions. Technicians and laboratory personnel were blinded to the disease status of participants. Fatty acid concentrations in whole plasma and erythrocytes were analyzed by gas-liquid chromatography in 2 separate runs. Blood samples of cases and controls identified in 1990–1994 were assayed in 2000–2001; case-control triplets identified in 1996 were assayed in 2002. A detailed description of laboratory process was published elsewhere (23).

Laboratory control samples were run along with the case-control samples. Within-run CVs (%) were assessed by repeatedly analyzing quality-control samples. The within-run CV for EPA was 8.5% (plasma) and 16.7% (erythrocytes); for DPA, it was 6.0% (plasma) and 5.2% (erythrocytes); for DHA, it was 5.6% (plasma) and 5.3% (erythrocytes); and for {alpha}-linolenic acid (ALA), it was 6.5% (plasma) and 6.5% (erythrocytes).

Assessment of covariates
Medical history, lifestyle risk factors, and dietary habits were assessed by means of validated questionnaires in 1990 (closest in time to the blood sampling). Usual diet habits were assessed and updated every 4 y since 1980 by validated semi-quantitative food-frequency questionnaires inquiring about food consumption in the previous year. A detailed description of the reproducibility and validity of the questionnaires was published elsewhere (24). Four questions inquired about the intake of canned tuna fish, dark-meat fish, other fish, and shellfish. Estimated dietary consumption of long-chain n–3 fatty acids, including EPA, DPA, and DHA, was calculated on the basis of the responses to these questions and the estimated nutrient contents of each portion from the Harvard Food Composition Database. Long-chain n–3 fatty acid intake from supplements was also taken into account, although only 4 cases and 7 controls reported the use of supplements.

Plasma total and HDL cholesterol and triacylglycerol were measured enzymatically on the Hitachi 911 analyzer (Roche Diagnostics, Basel, Switzerland). LDL cholesterol was measured by using a homogenous direct method (Genzyme, Cambridge, MA). A detailed description of laboratory methods and procedures was published elsewhere (25). Concentrations of E-selectin, interleukin-6, intercellular adhesion molecule 1, and vascular cell adhesion molecule 1 were measured by using a commercial enzyme-linked immunosorbent assay (R&D Systems, Minneapolis, MN). C-reactive protein concentrations were measured by using a high-sensitivity latex-enhanced immunonephelometric assay (Dade Behring, Deerfield, IL).

Statistical analysis
We assessed the correlation between plasma and erythrocyte long-chain n–3 fatty acids and self-reported consumption of fish (servings/wk) and long-chain n–3 fatty acids (% of total fat) among controls. Spearman partial-rank correlation coefficients were calculated to control for the effects of other variables (26), including energy intake (in MJ), age at phlebotomy (y), smoking status (never smoked, past smoker, or currently smoke 1–14 cigarettes/d, 15–24 cigarettes/d, or ≥25 cigarettes/d), body mass index (BMI; in kg/m2), fasting status (yes or no), postmenopausal status (yes or no), postmenopausal hormone use (never, past, or current), and assay batch. We used the t test to examine the significance of Spearman partial correlation coefficients according to the following equation (26):

Formula 1(1)
where r is the Spearman partial correlation coefficient, n is the sample size, and p is the number of parameters of covariates. This test statistic has t distribution with n–p–2 df.

Quartiles of long-chain n–3 fatty acids were constructed according to the distribution among controls. Because case-control triplets diagnosed in 1990–1994 and 1996 were measured in 2 different runs in 2 different time periods, we created run-specific quartiles and merged the data for analysis to account for the potential between-run laboratory variation. We used conditional logistic regressions to estimate the relative risks (RRs) of nonfatal MI associated with these biomarkers. In nested case-control studies using risk-set sampling, odds ratios derived from conditional logistic regressions are unbiased estimates of RRs that take into account the matching factors (27). In multivariate models, we further adjusted for established risk factors for CHD including BMI (< 25, 25–29, or ≥30), physical activity (in tertiles), alcohol intake (0, 1–4, 5–14, or ≥15 g/d), total fat intake (% of total calories), parental history of MI before age 65 y (yes or no), history of hypertension (presence or absence), history of hypercholesterolemia (presence or absence), history of diabetes (presence or absence), postmenopausal status (yes or no), and postmenopausal hormone use (never, past, or current). To evaluate whether ALA could explain the association between long-chain n–3 fatty acids and the risk of nonfatal MI, we also adjusted for ALA concentrations in blood. P values for linear trend were calculated by entering a continuous score based on the median value in each quartile of fatty acid into the models.

We used multivariable linear regressions to examine the linear trend of plasma triacylglycerol, HDL, and inflammatory markers across quartiles of total long-chain n–3 fatty acids in plasma and erythrocytes in controls after adjustment for age, fasting status, smoking status, BMI, postmenopausal status and hormone use, physical activity, alcohol and total fat intake, parental history of MI, total trans fatty acids and ALA in blood, and assay batch. We calculated least-squares means for each quartile of individual long-chain n–3 fatty acids by using robust estimators of variance (28). P values for linear trend were estimated by entering the median value of each quartile of individual n–3 fatty acid content into the model as an ordinal variable. We found similar correlations between long-chain n–3 fatty acids and triacylglycerol for fasting and nonfasting samples, and we therefore used the entire control group for analysis after adjustment for fasting status.

All P values were 2-sided (P < 0.05). The 95% CIs were calculated for RRs and least-squares means. Data were analyzed with SAS software (version 9.1; SAS Institute Inc, Cary, NC).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The baseline characteristics of study participants are shown in Table 1Go. As would be expected, nurses diagnosed with nonfatal MI had a higher body mass index, consumed less alcohol, and were more likely to have a history of diabetes, hypertension, hypercholesterolemia, and parental history of MI than were controls. We therefore adjusted for these factors in multivariate analyses. Cases had less favorable lipoprotein profiles than did controls. In both plasma and erythrocytes, DHA was more abundant than EPA and DPA. In unadjusted analyses, cases had a significantly lower content of each long-chain n–3 fatty acid in plasma than did controls. Of erythrocyte concentrations of n–3 fatty acids, only DPA concentrations were significantly lower in cases than in controls. In both plasma and erythrocytes, cases had higher concentrations of ALA than did controls.


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  		TABLE 1. Baseline characteristics of nonfatal myocardial infarction cases and controls: the Nurses' Health Study, 19901

 
Spearman partial correlation coefficients between the dietary intake of fish and long-chain n–3 fatty acids and the plasma and erythrocyte long-chain n–3 fatty acid concentrations among controls are shown in Table 2Go. Both DHA and EPA in plasma and erythrocytes correlated with dietary consumption of fish and estimated dietary long-chain n–3 fatty acids. In contrast, DPA in both plasma and erythrocytes had little correlation with dietary fish or long-chain n–3 fatty acid intake. ALA in blood was not correlated with intake of fish or total long-chain n–3 fatty acids (data not shown). Dietary ALA intake was weakly correlated with ALA concentrations in blood (correlation: 0.23 for plasma and 0.16 for erythrocytes). Long-chain n–3 fatty acids were modestly intercorrelated with each other in plasma (between DPA and EPA: correlation = 0.52; between DPA and DHA: correlation = 0.24; and between EPA and DHA: correlation = 0.47) and in erythrocytes (between DPA and EPA, correlation = 0.41; between DPA and DHA: correlation = 0.18; and between EPA and DHA: correlation = 0.42). None of the correlations between ALA and long-chain n–3 fatty acids were significant (P < 0.1 for all absolute values of these correlations).


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  		TABLE 2. Spearman partial correlation coefficients between long-chain n–3 fatty acids in plasma and erythrocytes and the intake of these fatty acids and fish among controls at baseline1

 
The associations of long-chain n–3 fatty acids in plasma and erythrocytes with the risk of nonfatal MI are shown in Table 3Go. Plasma EPA concentrations were significantly associated with a lower risk of nonfatal MI. After adjustment for CHD risk factors and ALA concentrations in plasma, persons in the highest plasma EPA and DPA quartile had 77% (95% CI: 45%, 91%; P for trend = 0.001) and 60% (95% CI: 18%, 80%; P for trend = 0.004) lower risk of nonfatal MI, respectively, than did persons in the lowest quartile. EPA and DPA in erythrocytes were associated with a trend toward a lower risk of nonfatal MI, but the association was attenuated and was no longer significant after adjustment for other risk factors. In contrast, neither plasma nor erythrocyte DHA content was significantly associated with the risk of nonfatal MI after multivariable adjustment. Total content of long-chain n–3 fatty acids (EPA+DPA+DHA) in plasma, but not erythrocytes, was associated with a trend toward a lower risk of nonfatal MI (P = 0.03). The change of associations before and after adjustment of ALA concentrations in blood was not substantial (data not shown). Further adjustment for other factors, such as total trans fatty acids in blood and intakes of fiber, folate, fruit and vegetables, vitamin E supplement, and red meat, did not appreciably alter these findings (data not shown). ALA concentrations in plasma and erythrocytes were associated with a higher but nonsignificant risk of nonfatal MI: the RRs of the highest quartile were 1.79 (95% CI: 0.89, 3.59; P for trend = 0.14) for plasma ALA and 1.43 (95% CI: 0.73, 2.80; P for trend = 0.13) for erythrocyte ALA.


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  		TABLE 3. Relative risks of nonfatal myocardial infarction associated with long-chain n–3 fatty acid contents in plasma and erythrocytes: the Nurses' Health Study, 19901

 
We also evaluated associations between these n–3 fatty acids and concentrations of cardiovascular risk factors (Table 4Go). After multivariate adjustment, all individual long-chain n–3 fatty acids except DPA and DHA in erythrocytes were significantly inversely associated with triacylglycerol concentrations. The correlations were strongest for EPA in plasma. In addition, plasma EPA and DPA were positively associated with HDL cholesterol. Inverse correlations with some inflammatory markers were also seen for long-chain n–3 fatty acids in plasma. For example, strong inverse correlations were found between plasma EPA and DHA concentrations and plasma E-selectin concentrations. DPA in plasma also was strongly associated with lower concentrations of plasma interleukin-6. Long-chain n–3 fatty acids in erythrocytes were generally not associated with these inflammatory markers except for a positive association between erythrocyte EPA content and plasma C-reactive protein concentration.


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  		TABLE 4. Least-squares means of concentrations of plasma lipoprotein and inflammatory markers according to quartile of plasma and erythrocyte content of individual long-chain n–3 fatty acid among controls at baseline1

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
In this nested case-control study, higher concentrtions of EPA and DPA in plasma were associated with a lower risk of nonfatal MI among women. Based on the correlations between the tissue concentrations and estimated dietary consumption of these n–3 fatty acids, these findings may partly reflect dietary consumption but, particularly for DPA, may indicate important risk differences based on metabolism of long-chain n–3 fatty acids.

Long-chain n–3 fatty acids—ie, EPA (20:5n–3), DPA (22:5n–3), and DHA (22:6n–3)—have been hypothesized to be the constituents of the diet of Greenland Eskimos that are the major explanation for their low CHD mortality (29). In Western diets, seafood, especially dark-meat fish, is the primary dietary source of these fatty acids. In several well-conducted prospective cohort studies that assessed multiple CHD outcomes, fish intake was associated with lower risk of fatal CHD or sudden cardiac death but not with risk of nonfatal MI (2, 4, 5, 15, 16). Studies using biomarker data of long-chain n–3 fatty acid intake have also found significant inverse associations with sudden cardiac death (6, 30). In addition, in a secondary-prevention randomized trial conducted among MI survivors, supplementation with 1 g EPA + DHA/d significantly reduced the risk of sudden death by 45% but had no effects on nonfatal MI (13). These data support the proposed antiarrhythmic effects of EPA and DHA (10, 12).

Fewer studies have evaluated the relations of tissue concentrations of long-chain n–3 fatty acids and the risk of nonfatal MI, and their results have been inconsistent (14, 17, 18). Other biomarker studies that examined total CHD (combined nonfatal MI and fatal CHD) as the major outcome also have yielded mixed results (31, 32). In this study, EPA and DPA in blood, particularly in plasma, were associated with lower incidence of nonfatal MI after adjustment for other risk factors. It is interesting that we observed significantly inverse associations of DPA concentrations with risk, despite the fact that DPA was not correlated with estimated dietary consumption of n–3 fatty acids. Conversely, DHA content in plasma and erythrocytes was correlated with estimated dietary consumption but was not significantly associated with the risk of nonfatal MI.

Because the metabolisms for individual long-chain n–3 fatty acids are quite different, concentrations of these fatty acids in human blood may have different biological meanings. In both prior studies (33, 34) and the present analysis, DHA in plasma or erythrocytes is a better marker of dietary fish and n–3 fatty acid intake than is EPA. Blood concentrations of EPA could be influenced by several nondietary factors. EPA is preferentially mobilized from adipose tissue into the bloodstream at a much higher rate than is DHA (35). Compared with DHA, EPA is more likely to be distributed in the outer phospholipids layer of cell membranes, especially in lecithin (36), which is dynamically exchanged with plasma lecithin (37). The more dynamic metabolism, mobilization, and incorporation of EPA than of DHA may explain why DHA is a better marker of dietary consumption. It is important that these characteristics of EPA suggest that plasma EPA may represent a more dynamic and readily available pool of long-chain n–3 fatty acids than does DHA. In both plasma and erythrocytes, EPA has been shown to have higher incorporation and wash-out rates than does DHA, which indicates that EPA in blood may be metabolically more active and more available than is DHA (38). In comparison with EPA and DHA, much less is known about the metabolism, mobilization, and incorporation of DPA in tissues. In humans, DPA can be formed by means of the elongation of EPA or the retroconversion of DHA; the former is the much more dominant process (39, 40). The rapid retroconversion of DPA to EPA in human blood fractions also suggests the possibility that DPA could serve as a storage pool for EPA (41). In the present study, higher correlations observed between DPA and EPA concentrations than between DPA and DHA concentrations support this notion. In addition, DPA concentrations were not correlated with dietary fish or n–3 fatty acid consumption, which suggests that metabolic influences are the predominant determinants of DPA concentrations in plasma and erythrocytes. Therefore, either DPA itself or the processes related to DPA metabolism may play an important role in the risk of developing nonfatal MI.

Although ALA can be converted to long-chain n–3 fatty acids in vivo, the significance of this contribution in humans was unclear (42). In the current analysis, ALA was not correlated with the concentrations of these long-chain n–3 fatty acids. Adjustment of ALA did not substantially change the associations for these long-chain n–3 fatty acids, which suggested that ALA was unlikely to explain the inverse associations for EPA and DPA. Data on tissue or blood concentratins of ALA in relation to CHD risk were limited, and their results were mixed (43). In the current study, ALA concentrations in blood were not significantly associated with the risk of nonfatal MI. However, we cannot entirely exclude the possibility that, if ALA reduces the risk of CHD primarily through conversion to EPA, then women with a higher capacity for this conversion may have a lower risk of CHD.

Multiple potential effects of long-chain n–3 fatty acids may lower the risk of nonfatal MI. In vivo and in vitro, these fatty acids can reduce the production of atherogenic eicosanoids (44), improve endothelial dysfunction (45), and modulate plasma lipids (46). In the present study, plasma concentrations of EPA and DPA and, to a lesser extent, DHA were associated with more favorable concentrations of triacylglycerol, HDL cholesterol, and several inflammatory markers. By means of a dynamic exchange of cholesterol-ester and phospholipids (37, 47), circulating EPA and DPA in plasma may enter tissues and cell membranes and may modulate the production of atherogenic molecules, such as inflammatory mediators or atherogenic lipids, by affecting cell membrane receptors or binding to transcriptional factors or nuclear receptors, such as peroxisome proliferator–activated receptors, sterol regulatory element–binding protein, and nuclear factor-kappa B (48). Conversely, in the present study, n–3 fatty acids in erythrocytes were generally not associated with plasma concentrations of inflammatory markers. This observation is probably due to the fact that fatty acids in plasma phospholipids or cholesterol-esters are directly available to tissue cells, whereas only 60% of erythrocyte phospholipids can be exchanged into circulation (37).

Two recent Japanese studies indicated that high levels of fish intake or EPA supplementation may significantly lower the risk of nonfatal coronary events (19, 20). Because the usual fish intake in Japan is substantially higher than that in typical Western populations, it is not clear whether these results are generalizable to other populations. For example, as indicated by our findings for DHA, the current level of fish intake in the United States may not be sufficient to prevent nonfatal MIs. Furthermore, the efficacy of fish intake or fish-oil use in preventing total cardiovascular diseases is still a matter of debate (49-52). However, our study raises the possibility that increasing the availability of circulating EPA and DPA in plasma (through dietary intake or changes in mobilization, enzymatic activities of elongases and desaturases, or incorporation that facilitates the availability of EPA and DPA) may be beneficial to the prevention of CHD, independent of antiarrhythmic effects of long-chain n–3 fatty acids.

Several potential limitations should be considered. First, although we carefully controlled for major known CHD risk factors in the analyses, we cannot entirely exclude the possibility that the observed associations were due to other associated healthy lifestyles or dietary patterns. However, the strongest associations were seen for EPA and DPA, which were less strongly associated with dietary consumption than was DHA. Second, greater measurement error for erythrocyte EPA (within-run CV: 16.7%) may have substantially decreased statistical power to detect associations between erythrocyte EPA and nonfatal MI. Third, these findings may not be generalized to populations other than that of the present study—ie, white nurses.

In conclusion, this prospective study provides new evidence that plasma concentrations of EPA and DPA are associated with a lower incidence of nonfatal MI among US women. These results suggest that blood concentrations of individual long-chain n–3 fatty acids, which reflect both dietary intake and metabolic influences, may have important biological effects on cardiovascular risk beyond antiarrhythmic effects.


   ACKNOWLEDGMENTS
 
The authors' responsibilities were as follows: QS: analyzed the data and drafted the manuscript; JM: designed the study and directed the blood sample assays; HC: designed the study, assayed the biomarkers, and prepared the data; KMR and CMA: designed the study and collected the data; DM and FBH: designed the analytic strategy and supervised the data analysis; and all authors: contributed to the critical revision of the manuscript. None of the authors had a financial or personal conflict of interest.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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Received for publication January 24, 2008. Accepted for publication March 27, 2008.




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