Table 1.
Characteristics of the identified 16 studies including 18 prospective cohorts that evaluated dietary n-3 PUFA, fish/seafood consumption, or biomarker n-3 PUFA levels and incidence of type 2 diabetes*
| Author (Year) | Study name (Country) | Total N/number of DM cases | Mean Age, y | Mean BMI, kg/m2 | Men, % | Follow-up years | Exposures† | Diabetes ascertainment | Adjustment‡ | Quality score§ | Additional data requested/provided|| |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Meyer (2001)(36) | Iowa Women’s Health Study (USA) | 35,988/1,890 | 62 | 26.9 | 0 | Max: 11 |
Diet EPA+DHA |
Self-report. Validated in sub-cohort by physician diagnosis | +++ | 3 | Yes/No |
| van Dam (2002)(40) | Health Professional Follow-up Study (HPFS) (USA) | 42,504/1,321 | 54 | 25.5 | 100 | Mean: 11 |
Diet ALA |
Self-report confirmed by supplemental questionnaire | +++ | 5 | No/- |
| Wang (2003)(44) | Atherosclerosis Risk in Communities Study (USA) | 2,909/252 | 54 | 26.7 | 46.9 | Mean: 8.1 |
Biomarker ALA |
Self-reported diabetes medication use or physician diagnosis or fasting or non fasting glucose | ++ | 4 | Yes/Yes |
| Hodge (2007)(32) | Melbourne Collaborative Cohort Study (Australia) | ¶3,737/346 | 55 | 27 | 44.1 | Mean: 4.1 |
Diet ALA EPA DHA EPA+DHA Biomarker ALA EPA DHA EPA+DHA |
Self-report confirmed by subject’s physician. | ++ | 4 | Yes/Yes |
| Krachler (2008)(34) | Vasterbotten Intervention Program (Sweden) | ¶450/159 | 52 | 27 | 58.4 | Mean: 8.8 |
Biomarker ALA EPA DHA EPA+DHA |
Subjects attended health exam at local primary care center, diabetes confirmed according to WHO 1998 criteria. | ++ | 4 | Yes/Yes |
| Vang (2008)(42) | Adventist Mortality Study and Adventist Health Study (USA) | 8,401/531 | 65 | 24.5 | 61 | Mean: 16 |
Diet Seafood EPA+DHA** |
Self-report. | + | 1 | Yes/No |
| Kaushik (2009)(33) | Nurses’ Health Study (NHS) (USA) | 61,031/4,159 | 52 | 24.9 | 0 | Mean: 16.7 |
Diet Fish EPA+DHA |
Self-report confirmed by supplementary questionnaire. | +++ | 5 | No/No |
| Kaushik (2009)(33) | Nurses’ Health Study 2(NHS2) (USA) | 91,669/2,728 | 36 | 24.5 | 0 | Mean: 13.7 |
Diet Fish EPA+DHA |
Self-report confirmed by supplementary questionnaire. | +++ | 5 | No/No |
| Kaushik (2009)(33) | Health Professional Follow-up Study (HPFS) (USA) | 42,504/2493 | 53 | 24.9 | 100 | Mean: 16.0 |
Diet Fish EPA+DHA |
Self-report confirmed by supplementary questionnaire. | +++ | 5 | No/No |
| Patel (2009)(39) | EPIC-Norfolk (UK) | 21,984/725 | 58 | 26.3 | 44.6 | Median: 10.2 |
Diet Seafood EPA+DHA** |
Self-report confirmed by linkage with health registries or cases detected by linkage to health registries alone. | +++ | 5 | Yes/Yes |
| van Woudenbergh (2009)(41) | Rotterdam study (Netherlands) | 4,472/463 | 67 | 26.2 | 41 | Median: 12.4 |
Diet Fish EPA DHA EPA+DHA |
Diabetes status confirmed by general practitioners according to WHO 1999 criteria. | +++ | 4 | Yes/Yes |
| Patel (2010)(38) | EPIC-Norfolk (UK) | ¶383/199 | 64 | 28.1 | 53.3 | Mean: 10.3 |
Diet ALA EPA DHA Biomarker ALA EPA DHA EPA+DHA |
Self-report confirmed by linkage with health registries. | ++ | 4 | Yes/Yes |
| Brostow (2011)(29) | Singapore Chinese Health Study (Singapore) | 43,176/2,252 | 55 | 23 | 42.4 | Mean: 5.7 |
Diet Fish Seafood ALA EPA+DHA |
Self-report confirmed by linkage with hospital records or supplementary questionnaire | +++ | 5 | Yes/Yes |
| Djousse (2011)(31) | Women’s Health Study (WHS) (USA) | 36,328/2,370 | 55 | 25.9 | 0 | Mean: 12.4 |
Diet Fish ALA EPA DHA EPA+DHA |
Self-report confirmed by telephone interview or supplemental questionnaire | +++ | 5 | Yes/Yes |
| Djousse (2011)(30) | Cardiovascular Health Study (CHS) (USA) | 3,088/204 | 75 | 26.4 | 38.9 | Mean: 9.6 |
Diet Fish ALA EPA+DHA Biomarker ALA EPA DHA EPA+DHA |
Diabetes medication use, or fasting or nonfasting glucose level | +++ | 4 | Yes/Yes |
| Kroger (2011)(35) | EPIC-Potsdam (Germany) | 2,724/673 | 51 | 26.9 | 43.5 | Mean: 6.3 |
Diet ALA EPA DHA EPA+DHA Biomarker ALA EPA DHA EPA+DHA |
Self-report confirmed by diagnosing physician | +++ | 4 | Yes/Yes |
| Nanri (2011)(37) | JPHC-Men (Japan) | 22,921/572 | 56 | 23.6 | 100 | Mean: 5 |
Diet Seafood EPA+DHA** |
Self-report validated by medical records in sub-group | +++ | 5 | No/- |
| Nanri (2011)(37) | JPHC-Women (Japan) | 29,759/399 | 56 | 23.4 | 0 | Mean: 5 |
Diet Seafood EPA+DHA** |
Self-report validated by medical records in sub-group | +++ | 5 | No/- |
| Villegas (2011)(43) | Shanghai Men’s Health Study (SMHS) (China) | 51,963/900 | 54 | 23.6 | 100 | Mean: 4 |
Diet Fish Seafood EPA+DHA |
Self-report confirmed by diabetes medication use or fasting glucose or OGTT. | +++ | 5 | Yes/Yes |
| Villegas (2011)(43) | Shanghai Women’s Health Study (SWHS) (China) | 64,193/3,034 | 51 | 23.8 | 0 | Mean: 8.9 |
Diet Fish Seafood EPA+DHA |
Self-report confirmed by diabetes medication use or fasting glucose or OGTT. | +++ | 5 | Yes/Yes |
EPIC, European Prospective Investigation into Cancer and Nutrition; JPHC, Japan Public Health Center-based Prospective Study; Fish, refers to finfish; Seafood, refers to finfish and shellfish combined.
All exposure-type 2 diabetes risk assessments were pre-specified primary analyses, except dietary fish/n-3 PUFA intake in Djousse et al (30), which were secondary analyses.
Dietary exposures were all assessed using food frequency questionnaires; fatty acid biomarkers were measured in plasma phospholipids (30; 32; 38; 44), plasma cholesterol esters (44); red blood cell membranes (34); red blood cell phospholipids (35; 38), by gas or gas-liquid chromatography.
Degree of covariate adjustment indicated by (+): sociodemographics; (++): sociodemographics and other risk factors; (+++):sociodemographics and other risk factors and dietary variables.
Quality of each study was assessed by 5 separate criteria on an integer scale (0 or 1, with 1 being better). These included: appropriateness and reporting of inclusion and exclusion criteria, assessment of exposure (1 point if habitual n-3 PUFA/fish/seafood consumption was assessed with a validated diet assessment method, i.e. a validated FFQ or repeated short term measures; for biomarkers, a published laboratory assay), assessment of outcome (1 point if diagnosis of DM was confirmed according to accepted criteria and not based on self report), control of confounding (1 point if adjusted for socio-demographic plus either other risk factors or dietary variables for dietary studies; 1 point if adjusted for socio-demographic plus other risk factors for biomarker studies) and evidence of bias (1 point if no evidence of bias). Scores were summed and studies with scores from 0 to 3 and 4 to 5 were considered lower and higher quality, respectively.
Dependent on the study, additional data requested included baseline characteristics (age, BMI, exposure distributions) and exposure category-specific data (number of participants, person-years of follow-up, number of cases, median level of exposure, risk estimates and 95% CI).
Nested selection of cases and controls within the original cohort. The total number of participants recruited in the original cohorts were: Melbourne Collaborative Cohort Study, n=41,528 (32); Vasterbotton intervention program (34), n=33,336; EPIC-Norfolk, n=25,639 (38).
Dietary EPA+DHA in these studies were imputed from fish/seafood intake by using a conversion factor calculated from nationally representative dietary surveys as part of our work in the Global Burden of Diseases study (48).