The role of dietary measurement error in investigating the hypothesized link between dietary fat intake and breast cancer--a story with twists and turns

Reflection on modern methods: five myths about measurement error in epidemiological research

Epidemiologists are often confronted with datasets to analyse which contain measurement error due to, for instance, mistaken data entries, inaccurate recordings and measurement instrument or procedural errors. If the effect of measurement error is misjudged, the data analyses are hampered and the validity of the study's inferences may be affected. In this paper, we describe five myths that contribute to misjudgments about measurement error, regarding expected structure, impact and solutions to mitigate the problems resulting from mismeasurements. The aim is to clarify these measurement error misconceptions. We show that the influence of measurement error in an epidemiological data analysis can play out in ways that go beyond simple heuristics, such as heuristics about whether or not to expect attenuation of the effect estimates. Whereas we encourage epidemiologists to deliberate about the structure and potential impact of measurement error in their analyses, we also recommend exercising restraint when making claims about the magnitude or even direction of effect of measurement error if not accompanied by statistical measurement error corrections or quantitative bias analysis. Suggestions for alleviating the problems or investigating the structure and magnitude of measurement error are given.

Cancer incidence and associations with known risk and protective factors: the Alaska EARTH study

PURPOSE

Cancer is the leading cause of mortality among Alaska Native (AN) people. The Alaska Education and Research Towards Health (EARTH) cohort was established to examine risk and protective factors for chronic diseases, including cancer, among AN people. Here, we describe the cancer experience of the Alaska EARTH cohort in relation to statewide- and region-specific tumor registry data, and assess associations with key cancer risk factors.

METHODS

AN participants were recruited into the Alaska EARTH cohort during 2004-2006. Data collected included patient demographic, anthropometric, medical and family history, and lifestyle information. This study linked the Alaska EARTH data with cancer diagnoses recorded by the Alaska Native Tumor Registry (ANTR) through 12/31/15. We compared EARTH incidence to ANTR statewide incidence. We examined independent associations of smoking status, diet, BMI, and physical activity with incident all-site cancers using multivariable-adjusted Cox proportional hazards models.

RESULTS

Between study enrollment and 2015, 171 of 3,712 (4.7%) Alaska EARTH study participants were diagnosed with cancer. The leading cancers among Alaska EARTH participants were female breast, lung, and colorectal cancer, which reflected those observed among AN people statewide. Incidence (95% CI) of cancer (all sites) among Alaska EARTH participants was 629.7 (510.9-748.6) per 100,000 person-years; this was comparable to statewide rates [680.5 (660.0-701.5) per 100,000 population]. We observed lower risk of all-sites cancer incidence among never smokers.

CONCLUSIONS

Cancer incidence in the Alaska EARTH cohort was similar to incidence observed statewide. Risk and protective factors for leading cancers among AN people mirror those observed among other populations.

Dairy product consumption and its association with metabolic disturbance in a prospective study of urban adults

The role of dairy foods and related nutrients in cardiometabolic health aetiology is poorly understood. We investigated longitudinal associations between the metabolic syndrome (MetS) and its components with key dairy product exposures. We used prospective data from a bi-racial cohort of urban adults (30-64 years at baseline (n 1371)), the Healthy Aging in Neighborhoods of Diversity across the Life Span (HANDLS), in Baltimore City, MD (2004-2013). The average of two 24-h dietary recalls measured 4-10 d apart was computed at baseline (V1) and follow-up (V2) waves. Annual rates of change (Δ) in dairy foods and key nutrients were estimated. Incident obesity, central obesity and the MetS were determined. Among key findings, in the overall urban adult population, both cheese and yogurt (V1 and Δ) were associated with an increased risk of central obesity (hazard ratio (HR) 1·13; 95 % CI 1·05, 1·23 per oz equivalent of cheese (V1); HR 1·21; 95 % CI 1·01, 1·44 per fl oz equivalent of yogurt (V1)]. Baseline fluid milk intake (V1 in cup equivalents) was inversely related to the MetS (HR 0·86; 95 % CI 0·78, 0·94), specifically to dyslipidaemia-TAG (HR 0·89; 95 % CI 0·81, 0·99), although it was directly associated with dyslipidaemia-HDL-cholesterol (HR 1·10; 95 % CI 1·01, 1·21). Furthermore, ΔCa and ΔP were inversely related to dyslipidaemia-HDL and MetS incidence, respectively, whereas Δdairy product fat was positively associated with incident TAG-dyslipidaemia and HDL-cholesterol-dyslipidaemia and the MetS. A few of those associations were sex and race specific. In sum, various dairy product exposures had differential associations with metabolic disturbances. Future intervention studies should uncover how changes in dairy product components over time may affect metabolic disorders.

Plasma enterolactone and risk of prostate cancer in middle-aged Swedish men

Purpose

Enterolactone (ENL) is formed in the human gut after consumption of lignans, has estrogenic properties, and has been associated with risk of prostate cancer. We examined the association between plasma ENL levels and prostate cancer in a nested case–control study within the population-based Malmö Diet and Cancer cohort. We also examined the association between plasma ENL and dietary and lifestyle factors.

Methods

The study population consisted of 1010 cases occurring during a mean follow-up of 14.6 years, and 1817 controls matched on age and study entry date. We used national registers (95%) and hospital records (5%) to ascertain cases. Diet was estimated by a modified diet history method. Plasma ENL concentrations were determined by a time-resolved fluoroimmunoassay. Odds ratios were calculated by unconditional logistic regression.

Results

There were no significant associations between plasma ENL and incidence of all prostate cancer (odds ratio 0.99 [95% confidence interval 0.77–1.280] for the highest ENL quintile versus lowest, p for trend 0.66). However, in certain subgroups of men, including men with abdominal obesity (p for interaction = 0.012), we observed associations between high ENL levels and lower odds of high-risk prostate cancer. Plasma ENL was positively associated with consumption of high-fibre bread, fruit, tea, and coffee; with age, and with height, while it was negatively associated with smoking and waist circumference; however, although significant, all associations were rather weak (r ≤ |0.14|).

Conclusion

ENL concentration was not consistently associated with lower prostate cancer risk, although it was weakly associated with a healthy lifestyle.

Electronic supplementary material

The online version of this article (doi:10.1007/s00394-017-1530-z) contains supplementary material, which is available to authorized users.

Invited Commentary: The Contribution to the Field of Nutritional Epidemiology of the Landmark 1985 Publication by Willett et al

The semiquantitative food frequency questionnaire (FFQ) has been the primary source of dietary exposure data in epidemiology for decades. Although frequency instruments had been evaluated before the 1985 publication "Reproducibility and Validity of a Semiquantitative Food Frequency Questionnaire" by Willett et al. (Am J Epidemiol. 1985;122(1):51-65), that paper was the prototype for the development and validation of what was then a highly innovative method for collecting dietary data. This approach was adopted in nearly all subsequent cohort studies of diet and disease. The paper also catalyzed an extended scientific discourse regarding methods for validation, energy adjustment, and measurement error. It is now well established that data from FFQs and other self-reported dietary assessment instruments have both value and error and that this error should be considered in the analysis and interpretation of findings, including sensitivity analyses in which adjustment for measurement error is explored. Advances in technology make it feasible to consider collecting multiple granular short-term instruments such as recalls or records over time in addition to FFQs among all participants in large cohort studies; both provide valuable information. Without a doubt, the 1985 publication by Willett et al. provided the foundation that propelled the field of nutritional epidemiology forward, and it continues to be relevant today.

Linoleic acid and breast cancer risk: a meta-analysis

Objective

Prior studies on linoleic acid, the predominant n-6 fatty acid, and breast cancer risk have generated inconsistent results. We performed a meta-analysis to summarize the evidence regarding the relationship of dietary and serum linoleic acid with breast cancer risk.

Design

Pertinent studies were identified by a search of PubMed and EMBASE. The fixed- or random-effect pooled measure was selected based on between-study heterogeneity.

Results

Eight prospective cohort studies and four prospective nested case–control studies, involving 10 410 breast cancer events from 358 955 adult females across different countries, were included in present study. Compared with the lowest level of linoleic acid, the pooled relative risk (RR; 95 % CI) of breast cancer was 0·98 (0·93, 1·04) for the highest level of linoleic acid. The pooled RR (95 % CI) for dietary and serum linoleic acid were 0·99 (0·92, 1·06) and 0·98 (0·88, 1·08), respectively. The RR (95 % CI) of breast cancer was 0·97 (0·91, 1·04), 0·95 (0·85, 1·07), 0·96 (0·86, 1·07), 0·98 (0·87, 1·10) and 0·99 (0·85, 1·14) for linoleic acid intake of 5, 10, 15, 20 and 25 g/d, respectively. The risk of breast cancer decreased by 1 % (RR=0·99; 95 % CI 0·93, 1·05) for every 10 g/d increment in linoleic acid intake.

Conclusions

This meta-analysis indicated that both dietary linoleic acid intake and serum linoleic acid level were associated with decreased risk of breast cancer, although none of the associations were statistically significant. Further investigations are warranted.

Erythrocyte saturated fatty acids and systemic inflammation in adults

OBJECTIVE

The role of saturated fatty acids (SFAs) in chronic disease remains controversial; inflammation is one pathway by which SFAs influence the risk for chronic disease. The aim of this study was to investigate the associations between red blood cell (RBC) phospholipid SFAs and systemic inflammation.

METHODS

As part of a randomized controlled trial, we measured RBC phospholipid FA composition in 55 generally healthy adults twice at 3-mo intervals. We estimated associations of RBC total SFAs and two major SFA subtypes, palmitic and stearic acids, with C-reactive protein (CRP), interleukin (IL)-6, white blood count (WBC), and a composite inflammation measure using generalized estimating equations in multivariable FA substitution models.

RESULTS

Mean (±SD) SFA level across both visits was 45% ± 3% of the total RBC FAs, mainly palmitic (21% ± 1%) and stearic (17% ± 3%) acids. In models adjusted for age, sex, race, smoking, body mass index, statin use, aspirin use, transunsaturated FAs, and ω-3 FAs, SFAs were significantly associated with IL-6 (20% increase per 1 SD increment; 95% confidence interval [CI], 0.03%-43%; P = 0.05) and the composite inflammation measure (P = 0.05) and marginally associated with CRP (34% increase; 95% CI, -1% to 81%; P = 0.06), but not associated with WBC. Stearic acid was positively associated with CRP (35% increase; 95% CI, 2%-79%; P = 0.04). Palmitic acid was marginally associated with the composite inflammation measure (P = 0.06) and, upon additional ω-6 FA adjustment, significantly associated with IL-6 (15% increase; 95% CI, 0.4%-27%; P = 0.006).

CONCLUSIONS

RBC SFAs, which represent longer-term dietary intake, are positively associated with inflammation. In particular, palmitic acid was associated with IL-6, and stearic acid was associated with CRP after multivariable adjustment.

Current evidence linking polyunsaturated Fatty acids with cancer risk and progression

There is increasing evidence that polyunsaturated fatty acids (PUFAs) play a role in cancer risk and progression. The n-3 family of PUFAs includes alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) while the n-6 family includes linolenic acid (LA) and arachidonic acid (AA). EPA and DHA are precursors for anti-inflammatory lipid mediators while AA is a precursor for pro-inflammatory lipid mediators. Collectively, PUFAs play crucial roles in maintaining cellular homeostasis, and perturbations in dietary intake or PUFA metabolism could result in cellular dysfunction and contribute to cancer risk and progression. Epidemiologic studies provide an inconsistent picture of the associations between dietary PUFAs and cancer. This discrepancy may reflect the difficulties in collecting accurate dietary data; however, it also may reflect genetic variation in PUFA metabolism which has been shown to modify physiological levels of PUFAs and cancer risk. Also, host-specific mutations as a result of cellular transformation could modify metabolism of PUFAs in the target-tissue. Clinical trials have shown that supplementation with PUFAs or foods high in PUFAs can affect markers of inflammation, immune function, tumor biology, and prognosis. Pre-clinical investigations have begun to elucidate how PUFAs may mediate cell proliferation, apoptosis and angiogenesis, and the signaling pathways involved in these processes. The purpose of this review is to summarize the current evidence linking PUFAs and their metabolites with cancer and the molecular mechanisms that underlie this association. Identifying the molecular mechanism(s) through which PUFAs affect cancer risk and progression will provide an opportunity to pursue focused dietary interventions that could translate into the development of personalized diets for cancer control.

A high diet quality is associated with lower incidence of cardiovascular events in the Malmö diet and cancer cohort

Aims

To investigate if diet quality is related to incidence of cardiovascular (CV) events.

Subjects and Methods

A diet quality index based on the 2005 Swedish Nutrition Recommendations and the Swedish Dietary Guidelines was created and included six dietary components: saturated fatty acids, polyunsaturated fatty acids, fish and shellfish, dietary fiber, fruit and vegetables, and sucrose. The index ranked 17126 participants (59% women) of the population-based Malmö Diet and Cancer cohort (Sweden) on their dietary intakes. Total index score was categorized as low, medium or high. Cox proportional hazard regression was used to model associations between index score categories and index components with risk of incident CV events, with adjustment for potential confounders. The incidence of first CV events (non-fatal or fatal myocardial infarction or ischemic stroke or death from ischemic heart disease) was monitored from baseline (1991–1996) until December 31, 2008; 703 CV events occurred in women and 1093 in men.

Results

A high diet quality was associated with decreased risk of CV events when compared to a low diet quality. In multivariate analysis, the risk reduction was 32% (hazard ratio = 0.68, 95% confidence interval: 0.49–0.73) in men and 27% (hazard ratio = 0.73, 95% confidence interval: 0.59–0.91) in women. When examined separately and mutually adjusted for each other, the individual components were either not associated with CV risk or marginally decreased risks were seen.

Conclusion

High quality diets in line with current recommendations may reduce the risk of CV events. This study illustrates the importance of considering a combination of dietary factors when evaluating diet-disease associations.

Sex-specific interactions between the IRS1 polymorphism and intakes of carbohydrates and fat on incident type 2 diabetes

BACKGROUND

The minor T allele of rs2943641 near the gene encoding for insulin receptor substrate 1 (IRS1) has been associated with decreased risk of type 2 diabetes (T2D) and adiposity in genome-wide association studies. Dietary intake can influence the regulation of IRS1, and studies have indicated sex-specific associations between IRS1 and adiposity.

OBJECTIVE

The objective was to examine the interaction between IRS1 rs2943641 and macronutrient intakes on incident T2D and percentage body fat in the Malmö Diet and Cancer cohort.

DESIGN

The study included 15,227 women and 9614 men aged 45-74 y without prevalent diabetes. Dietary data were collected with a modified diet history method. During 12 y of follow-up, 1567 incident T2D cases were identified.

RESULTS

The T allele was associated with lower incidence of T2D (P-trend = 0.003) and, in men, with higher percentage body fat (P-trend = 0.00002). We observed 3-way interactions between sex, rs2943641, and carbohydrate intake (P = 0.01) as well as between sex, rs2943641, and fat intake (P = 0.01) on incident T2D. Among women, the T allele was associated with decreased risk only in the lower tertiles of carbohydrate intake (P-trend = 0.01, P-interaction = 0.01). In contrast, among men, the T allele was associated with decreased risk in the lowest tertile of fat intake (P-trend = 0.01, P-interaction = 0.02). No interaction was observed between macronutrient intakes and rs2943641 on percentage body fat.

CONCLUSIONS

Our results indicate that IRS1 rs2943641 interacts with carbohydrate and fat intakes on incident T2D in a sex-specific fashion. A protective association between the rs2943641 T allele and T2D was restricted to women with low carbohydrate intake and to men with low fat intake.

Scoring models of a diet quality index and the predictive capability of mortality in a population-based cohort of Swedish men and women

Objective

To examine how different scoring models for a diet quality index influence associations with mortality outcomes.

Design

A study within the Malmö Diet and Cancer cohort. Food and nutrient intakes were estimated using a diet history method. The index included six components: SFA, PUFA, fish and shellfish, fibre, fruit and vegetables, and sucrose. Component scores were assigned using predefined (based on dietary recommendations) and population-based cut-offs (based on median or quintile intakes). Multivariate Cox regression was used to model associations between index scores (low, medium, high) and all-cause and cause-specific mortality by sex.

Setting

Malmö, the third largest city in Sweden.

Subjects

Men (n 6940) and women (n 10 186) aged 44–73 years. During a mean follow-up of 14·2 years, 2450 deaths occurred, 1221 from cancer and 709 from CVD.

Results

The predictive capability of the index for mortality outcomes varied with type of scoring model and by sex. Stronger associations were seen among men using predefined cut-offs. In contrast, the quintile-based scoring model showed greater predictability for mortality outcomes among women. The scoring model using median-based cut-offs showed low predictability for mortality among both men and women.

Conclusions

The scoring model used for dietary indices may have a significant impact on observed associations with disease outcomes. The rationale for selection of scoring model should be included in studies investigating the association between dietary indices and disease. Adherence to the current dietary recommendations was in the present study associated with decreased risk of all-cause and cause-specific mortality, particularly among men.

Pickled food and risk of gastric cancer--a systematic review and meta-analysis of English and Chinese literature

BACKGROUND

Ecological and experimental studies have suggested an increased risk of gastric cancer in relation to consumption of pickled vegetables in East Asia.

METHODS

We conducted a meta-analysis of epidemiologic observational studies to evaluate the existing evidence. Searching PubMed, Vip Chinese Periodical, and China National Knowledge Infrastructure databases, we found a total of 60 studies, 50 case-control, and 10 prospective. We compared gastric cancer risk in pickled vegetable/food users versus nonusers (11 studies) or versus those in the lowest reported category of use (49 studies). Pooled results were computed with random-effects models.

RESULTS

Among case-control studies, 30 showed significant increased risk and one showed significant decreased risk. Among prospective studies, two showed a significant increased risk but none showed a significant decreased risk. The OR (95% CI) was 1.52 (1.37-1.68) for the overall association, 1.56 (1.39-1.75) for case-control, and 1.32 (1.10-1.59) for cohort studies. The OR (95% CI) was 1.89 (1.29-2.77) in Korean, 1.86 (1.61-2.15) in Chinese, and 1.16 (1.04-1.29) in Japanese studies, and 1.14 (0.96-1.35) in studies from other countries. There was high heterogeneity in overall and subgroup analyses. There was little evidence for publication bias.

CONCLUSION

Our results suggest a potential 50% higher risk of gastric cancer associated with intake of pickled vegetables/foods and perhaps stronger associations in Korea and China.

IMPACT

The results of this study may offer ways to reduce the risk of gastric cancer in highly populated areas with high incidence of gastric cancer.

Diet assessment methods: a guide for oncology nurses

Diet may play a significant role in cancer prevention, disease progression, and treatment tolerance. An in-depth search of the literature revealed limited information geared toward nurses about diet assessment methods used in research. The purpose of this review is to synthesize the evidence regarding diet assessment methods important in oncology studies. The method used varied based on the study size, duration, and research question. For example, studies focusing on mean nutrient intake of a group used a 24-hour dietary recall, estimated food diary or dietary record, or food frequency questionnaire. Studies investigating usual nutrient intake predominately used multiple 24-hour dietary recalls, dietary records, biomarkers, or food frequency questionnaires. Measuring dietary intake accurately in a cost-effective manner is a difficult task. Selection of the appropriate assessment tool is critical for the generation of quality data. Oncology nurses are increasing their involvement in nutrition research, and the findings from this review may promote a better understanding of the published and ongoing research in this important field of study.

Dietary fiber and saturated fat intake associations with cardiovascular disease differ by sex in the Malmö Diet and Cancer Cohort: a prospective study

BACKGROUND

The aim of the study was to examine associations between intake of macronutrients and dietary fiber and incident ischemic cardiovascular disease (iCVD) in men and women.

METHODS

We used data from 8,139 male and 12,535 female participants (aged 44-73 y) of the Swedish population-based Malmö Diet and Cancer cohort. The participants were without history of CVD and diabetes mellitus, and had reported stable dietary habits in the study questionnaire. Diet was assessed by a validated modified diet history method, combining a 7-d registration of cooked meals and cold beverages, a 168-item food questionnaire (covering other foods and meal patterns), and a 1-hour diet interview. Sociodemographic and lifestyle data were collected by questionnaire. iCVD cases, which included coronary events (myocardial infarctions or deaths from chronic ischemic heart disease) and ischemic strokes, were ascertained via national and local registries. Nutrient-disease associations were examined by multivariate Cox regressions.

RESULTS

During a mean follow-up of 13.5 years, we identified 1,089 male and 687 female iCVD cases. High fiber intakes were associated with lower incidence rates of iCVD in women and of ischemic stroke in men. In post-hoc analysis, we discovered statistically significant interactions between intake of fiber and saturated fat; these interactions also differed between men and women (p<0.001).

CONCLUSIONS

In this well-defined population, a high fiber intake was associated with lower risk of iCVD, but there were no robust associations between other macronutrients and iCVD risk. Judging from this study, gender-specific nutrient analysis may be preferable in epidemiology.

Dietary fat and breast cancer in postmenopausal women according to ethnicity and hormone receptor status: the Multiethnic Cohort Study

Dietary fat has been widely studied as a risk factor for breast cancer, with little consistency in results. The Multiethnic Cohort Study (MEC) provides an opportunity to assess this relationship for possible heterogeneity across different racial/ethnic groups, as well as by stratification on several other variables associated with risk. Therefore, we investigated the associations between dietary fat, overall and by type, and breast cancer risk among 85,089 postmenopausal women who entered the MEC by completing a comprehensive dietary questionnaire in 1993 to 1996. During a mean follow-up of 12 years, 3,885 incident invasive breast cancer cases were identified. The multivariate HR [95% confidence interval (CI)] for the highest versus lowest quintile of intake was 0.94 (95% CI, 0.85-1.05) for total fat and 0.93 (95% CI, 0.83-1.04) for saturated fat. Other specific types of dietary fat, including individual fatty acids, were not related to risk of postmenopausal breast cancer. We found no heterogeneity in these null findings across the five ethnic groups. Furthermore, we found no evidence that the association between dietary fat and postmenopausal breast cancer risk differed by estrogen/progesterone receptor status, tumor stage, body mass index, hormone replacement therapy use, follow-up period, family history of breast cancer, and smoking status at baseline. In conclusion, this comprehensive prospective analysis in the MEC does not support a role of adult intake of dietary fat in the etiology of postmenopausal breast cancer.

Development of a diet quality index assessing adherence to the Swedish nutrition recommendations and dietary guidelines in the Malmö Diet and Cancer cohort

Objective

To develop a diet quality index (DQI) that assesses adherence to the Swedish nutrition recommendations (SNR) and the Swedish dietary guidelines (SDG).

Design

A cross-sectional study within the Malmö Diet and Cancer (MDC) cohort. A diet history method collected dietary data, a structured questionnaire lifestyle and socio-economic information, and anthropometric data were collected by direct measurements. The index (DQI-SNR) included six components: SFA, PUFA, fish and shellfish, dietary fibre, fruit and vegetables, and sucrose.

Setting

Malmö, Sweden.

Subjects

Men (n 4525) and women (n 8491) of the MDC cohort enrolled from September 1994 to October 1996.

Results

For participants with high DQI-SNR scores, nutrient and food intakes were close to recommendations. However, most of the study population exceeded the recommended intake for SFA (98 %) and few reached recommended intakes for dietary fibre (24 %), fruit and vegetables (32 %), vitamin D (18 %) and folate (2 %). A high DQI-SNR score was positively associated with age, physical activity, not smoking, past food habit change, education and socio-economic status. Individuals with high scores were more likely to have a diabetes diagnosis or experienced a cardiovascular event.

Conclusions

Results suggest that the DQI-SNR is a useful tool for assessing adherence to the SNR 2005 and the SDG in the MDC cohort. No index has previously been developed with the aim of evaluating adherence to the current dietary recommendations in Sweden. Further validation of the DQI-SNR, and evaluation of its utility, is needed.

Epidemiological and clinical studies of nutrition

In this review, we briefly summarize some of the key developments in nutritional epidemiology and cancer over the past two decades with a focus on the strengths and limitations of study designs and dietary assessment methods. We present the evidence on dietary fat, meat, fiber, antioxidant nutrients, and calcium in relation to carcinogenesis from large cohort studies and randomized clinical trials (RCTs) and refer to the conclusions of the 2007 World Cancer Research Fund/American Institute for Cancer Research summary report. One prominent theme that emerged is the lack of concordance of results from RCTs and observational studies. There are multiple potential reasons for these discrepancies, including differences in study population, dose and timing of the exposure, adherence to an intervention, length of follow-up, and the primary endpoint. Therefore, null findings of RCTs do not necessarily indicate a lack of effect for the tested dietary factors on cancer risk, as some of these nutrients may have chemopreventive effects if given at the right time and in the right dose. It is likely that potential benefits from diet are due to a combination of food constituents rather than single components acting in isolation. Future efforts need to recognize the integrative nature of dietary exposures and attempt to study nutrients in the larger context of the foods and diets in which they are consumed.

The sex-specific role of plasma folate in mediating the association of dietary quality with depressive symptoms

Folate deficiency has been implicated in the etiology of unipolar depression. In this study, we attempted to cross-link plasma folate, depressive symptoms, and dietary quality (or dietary intake of folate) together in a comprehensive framework, while examining effect modification of those associations by sex. This was a cross-sectional, population-based study of 1681 participants aged 30-64 y (Healthy Aging in Neighborhoods of Diversity across the Lifespan Study). Participants were administered the Center for Epidemiologic Studies Depression scale (CES-D). Measures of plasma folate and dietary intakes (2 24-h recalls) from which the 2005-Healthy Eating Index (HEI) was computed were available. Multivariate logistic regression and structural equation modeling (SM) were conducted. Compared with the lowest tertile, the middle and uppermost tertiles of plasma folate were associated with a 39-40% reduced odds of elevated CES-D (> or =16) among women [adjusted odds ratio (T(3) vs. T(1)) = 0.60 (95% CI = 0.42-0.86); P = 0.006]. Confounding of this association by HEI(total) was noted among both men and women, although dietary folate did not confound this association appreciably. In SM, plasma folate completely mediated the inverse HEI(total)-CES-D association among men only, specifically for HEI(2) (higher intakes of whole fruits), HEI(3) (total vegetables), HEI(5) (total grains), HEI(6) (whole grains), HEI(7) (milk), and HEI(12) (lower discretionary energy). Among women, HEI(total) and 4 components had an inverse direct effect on CES-D score, suggesting a mechanism that is independent of plasma folate. Depressive symptoms in our study may be alleviated by improving overall dietary quality, with plasma folate playing a potential mediating role only among men.

Marine n-3 polyunsaturated fatty acids in adipose tissue and breast cancer risk: a case-cohort study from Denmark

OBJECTIVE

The aim of this study was to investigate the association between the content of marine n-3 polyunsaturated fatty acids (PUFA) in adipose tissue, a biomarker for the long-term intake of seafood, and the subsequent development of breast cancer (BC).

DESIGN

We designed a case-cohort study based on a cohort of healthy Danish women, who in the 1990 s donated adipose tissue biopsies to a biobank in order to investigate the role of diet for the development of cancer and chronic disease. During follow-up, incident cases of BC were identified through national registries, and the content of n-3 PUFA in adipose tissue was compared between cases and the cohort sample.

RESULTS

During follow-up, 463 new cases of BC were identified. After adjusting for potential confounders, no significant association between the content of marine n-3 PUFA and BC was found. When comparing the highest with the lowest quintile, the hazard ratio (HR) was 0.96 (95% CI 0.64-1.43) for total marine n-3 PUFA, 0.84 (95% CI 0.58-1.23) for eicosapentaenoic acid (EPA), and 1.08 (95% CI 0.73-1.58) for docosahexaenoic acid (DHA).

CONCLUSION

This study does not indicate any association between the content of total or individual marine n-3 PUFA in adipose tissue and development of BC.

Assessing diet in longitudinal birth cohort studies

Diet is an important component of a person's environment. It is important for adults and particularly for mothers during pregnancy and while breast feeding, and for children in utero and during later growth and development. Measurement of the type and amount of foods consumed is complex. Here we describe the different methods that can be used, when and when not to use each one, and the importance of validation studies.

Folate intake, methylenetetrahydrofolate reductase polymorphisms, and breast cancer risk in women from the Malmö Diet and Cancer cohort

BACKGROUND

Single nucleotide polymorphisms (SNP) of the folate-metabolizing enzyme methylenetetrahydrofolate reductase (MTHFR) may modify associations between folate intake and breast cancer. We examined if the association between tertiles of dietary folate equivalents (DFE) and breast cancer was different in subgroups according to genotypes of the MTHFR 677 C>T (rs1801133) and 1298A>C (rs1801131) SNPs and if the polymorphisms per se were associated with breast cancer.

METHODS

This nested case-control study included 544 incident cases with invasive breast cancer and 1,088 controls matched on age and blood sampling date from the population-based Malmö Diet and Cancer cohort. Genotyping of the MTHFR SNPs was done with PCR-based matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Odds ratios (OR) were obtained by unconditional logistic regression.

RESULTS

DFE was positively associated with breast cancer in MTHFR 677CT/TT-1298AA women (P for trend = 0.01) but inversely associated in compound heterozygous women (P for trend = 0.01). Interaction was observed between DFE and the 1298C allele (P = 0.03). The 677T allele was associated with increased breast cancer risk in women above 55 years [multivariate adjusted OR, 1.34; 95% confidence interval (95% CI), 1.01-1.76] and an interaction was observed between the T allele and age (P = 0.03). Homozygosis for the 1298C allele was associated with increased risk in women between 45 and 55 years (multivariate adjusted OR, 1.89; 95% CI, 1.09-3.29).

CONCLUSION

In conclusion, a positive association between DFE and breast cancer was observed in MTHFR 677CT/TT-1298AA women but an inverse association was observed in 677CT-1298AC women. The 677T allele was associated with higher breast cancer risk in women above 55 years of age.

Meat consumption is associated with obesity and central obesity among US adults

BACKGROUND

Meats are high in energy and fat content, and thus may be associated with higher risk of obesity. Many controversies remain regarding the association between meat consumption (MC) and obesity.

OBJECTIVES

The aim of this study was to analyze the associations between MC and obesity assessed using body mass index (BMI > or = 30) and waist circumference (> or = 102 cm in men and > or = 88 cm in women) among US adults.

METHODS

Nationally representative data collected in the 1999-2004 National Health and Nutrition Examination Survey (NHANES) were used. Linear and logistic regression analyses were conducted to test the associations between MC and adiposity measures controlling for potential confounders.

RESULTS

Considerable differences existed in MC across sociodemographic groups among US adults. Those who consumed more meat had a much higher daily total energy intake, for example, those in the upper vs bottom quintiles consumed around 700 more kcal day(-1) (P<0.05). Regression models showed consistent positive associations between MC and BMI, waist circumference, obesity and central obesity, respectively. Using quintile 1 (low MC) as the reference, the association (odds ratio (OR) and 95% confidence interval (CI)) between total MC quintiles and obesity were 1.03 (0.88; 1.21; 2nd quintile), 1.17 (1.00; 1.38), 1.27 (1.08; 1.51) and 1.27 (1.08; 1.49; upper quintile), respectively; whereas that with central obesity was 1.13 (0.96-1.33), 1.31 (1.10; 1.54), 1.36 (1.17-1.60) and 1.33 (1.13; 1.55), respectively.

CONCLUSIONS

These US national cross-sectional data show positive associations between MC and risk for obesity and central obesity.

Associations between dietary methods and biomarkers, and between fruits and vegetables and risk of ischaemic heart disease, in the EPIC Norfolk Cohort Study

BACKGROUND

Methods for assessing diet are prone to measurement error, which may be substantial in large cohort investigations. Biomarkers can be used as objective measures with which to compare estimates of nutritional exposure using different methods

METHODS

Cross sectional comparisons in 12 474 men and women of regression between biomarkers for vitamin C, sodium, potassium, fibre, carbohydrate, fat and phytoestrogens with intakes derived from food diaries and food frequency questionnaires (FFQ), and odds ratios for risk of ischaemic heart disease (IHD) by dietary and plasma vitamin C.

RESULTS

There were strong (P < 0.001) associations between biomarkers and intakes as assessed by food diary. Coefficients were markedly attenuated for data obtained from the FFQ, especially so for vitamin C, potassium and phytoestrogens (Z P < 0.05). Risk of IHD was associated with plasma vitamin C (P < 0.001) and intake of vitamin C and fruit and vegetables assessed by food diary (P quintile trends <0.001, 0.001) but not by the FFQ (P quintile trends 0.923, 0.186).

CONCLUSIONS

Nutritional data that reflect the findings from biomarkers reduce measurement error and will thus improve statistical power in studies of gene nutrient interactions in cohort studies.