Consumption of fish and stroke.

Background: In the past, at least 3 systematic reviews were published relating fish consumption to stroke. Results from these systematic reviews are discussed briefly:

  • He K. 2004: Examined the relation with stroke risk. 8 cohorts were included with 3,491 stroke events. Three cohorts were not identified/discussed (Lapidus L [6], Kinjo Y [10], Nagata C [23]).
    The authors found a significant protective effect against stroke risk based on the relative risk (RR = 0.69; 95% CI = 0.54-0.88), but not on the P-value (P = 0.06) for consumption ≥ 5 times/week vs < once/month.
  • Wang C. 2004: Examined the relation with stroke risk. 9 cohorts were included. In one of these cohorts, the association with total omega-3 fatty acids, rather than marine omega-3 fatty acids was examined (Seino F. 1997), so these results were not included in my review. Three cohorts were not identified/discussed (Lapidus L [6], Nagata C [23], Sauvaget C [27]).
    The authors of this review stated that inconsistent findings were done (pages 70-71, 73).
  • Bouzan C. 2005: This review only included articles identified by Wang C. (2004) in the review mentioned above. And the authors wanted to describe the dose-response relationship for fish consumption and stroke risk. 4 cohorts, and 1 case-control study were included, and 4 cohorts were excluded (Keli SO [1], Kinjo Y [10], Morris MC [15], Yuan JM [19]), in addition to the cohort examining total omega-3 fatty acids mentioned above (Seino F. 1997). Three cohorts were not identified/discussed (Lapidus L [6], Nagata C [23], Sauvaget C [27]).
    The authors found that one serving/week of fish decreased stroke risk by 12%. And that any increment of one additional serving/week, decreased risk by an additional 2%.

|Additional references:
Bouzan C. A quantitative analysis of fish consumption and stroke risk. Am J Prev Med. 2005 Nov;29(4):347-52. Abstract
He K. Fish consumption and incidence of stroke: a meta-analysis of cohort studies. Stroke. 2004 Jul;35(7):1538-42. Full text
Seino F. Dietary lipids and incidence of cerebral infarction in a Japanese rural community. J Nutr Sci Vitaminol (Tokyo). 1997 Feb;43(1):83-99. Abstract
Wang C. Effects of omega-3 fatty acids on cardiovascular disease. Evid Rep Technol Assess (Summ). 2004 Mar;(94):1-8. Full text|



Results:
Total stroke risk. Data about total fish consumption was provided by 22 cohorts, including 21,290 cases.
Significant protective effects were found in 4 cohorts (Kinjo Y [10], Mozaffarian D [24], Sauvaget C [27], Larsson SC [42]), and in two subcohorts among white women, and black men/women (Gillum RF [17]). These analysis' included 15,156 cases (71% of all cases).
A significantly increased risk was found in two other cohorts (Wennberg M [22] among men only, and Ness AR [31]).
The average RR could be calculated from 21 cohorts: RR = 0.87. One cohort attributed greatly to the total amount of cases (Kinjo Y [10]), but exclusion of this cohort from the analysis did not change the effect size materially: RR = 0.88.
Ischemic stroke risk. Data about total fish consumption was provided by 10 cohorts, including 8,382 cases.
Significant protective effects were found in 2 US cohorts (He K [14], Mozaffarian D [24]), including 914 cases (11% of all cases). The RR, but not the trend was significant in one of these cohorts (He K [14]). No (non)significantly increased risks were found. The average RR = 0.91.
Hemorrhagic stroke risk. Data about total fish consumption was provided by 10 cohorts, including 6,250 cases.
Significant protective effects were found in 2 Asian cohorts (Kinjo Y [10], Sauvaget C [27]), including 5,127 cases (82% of all cases). No (non)significantly increased risks were found. The average RR = 0.89.

Intermediate levels of consumption: Protective effects seemed get stronger with increasing levels of consumption (RR = 0.98, 0.94, 0.93, and 0.89 for < 1, 1, 2, and ≥ 3 servings fish/wk, respectively. But these effects depended on data from one single cohorts (Kinjo Y [10]). After exclusion of this cohort, all effects became stronger (RR = 0.97, 0.89, 0.86, and 0.86 for < 1, 1, 2, and ≥ 3 servings fish/week, respectively. A more detailed analysis can be found here.
Effect modification: A detailed analysis can be found here. Briefly, stratified analysis showed the following effects:

  • Data about men was available from 11 cohorts (3,929 cases). A significantly increased risk was found in 1 cohort (Wennberg M [22]). No other associations were found. The average RR = 0.99.
    Data about women was available from 9 cohorts (4,309 cases). Significant protective effects were found in 2 cohorts (Gillum RF [17], Larsson SC [42]), including 1,931 cases (45% of all cases). And nonsignificant protective effects were found in another 2 cohorts (Iso H [14], Iso H [36]), including 1,588 cases (37% of all cases). The average RR = 0.80.
  • Protective effects were found among US cohorts (RR = 0.77) and Asian cohorts (RR = 0.87), but not among European cohorts (RR = 0.96).
  • Protective effects among US cohorts were found against ischemic stroke risk, while protective effects among Asian cohorts were found against hemorrhagic stroke risk.
  • No consistent effect modification was found by other factors.

Subjects with prevalent disease. In one cohort, a significant protective effect was found against total stroke risk. And this effect was not modified by diabetes or prevalent CHD (Mozaffarian D [2005]).

Conclusion: Significant protective effects against total stroke risk were found in 6 out of 22 cohorts, 3 of which were of moderate-very large size. These cohorts included 71% of all cases. High fish consumption possibly protects against total stroke risk (- 13%). Effect sizes were identical for intakes of 2 and ≥ 3 servings/week. Stratified analysis showed that the evidence for a protective effect was restricted to Asian/US cohorts only, and women only.
Stratified analysis shows that the protective effect against total stroke risk among US cohorts is possibly caused by a protective effect against ischemic stroke risk, while the protective effect against total stroke risk among Asian cohorts is possibly caused by a protective effect against hemorrhagic stroke risk.

Prospective studies of total fish and total stroke risk:
AuthorCohort nameCasesEnd pointRelative Risk (RR)
42) Larsson SC (2011)The Swedish Mammography Cohort1,680RiskRR = 0.84 (0.71-0.98; P = 0.049)
38) Kaushik S (2008)The Blue Mountains Eye Study69MortalityHR = 0.62 (0.35-1.10)
36) Yamagishi K (2008)The JACC Study972MortalityHR = 0.91 (0.74-1.13; P = 0.40)
35) Bravata DM (2007)No cohort name defined369RiskHR = 0.89 (0.59-1.36)
34) Myint PK (2006)The EPIC-Norfolk Study217 men, and

204 women
RiskMen: RR = 1.34 (0.93-2.93; P = 0.26).

Women: RR = 0.86 (0.60-1.24; P = 0.29).
32) Nakamura Y (2005)The NIPPON DATA80288MortalityRR = 1.28 (0.71-2.32; P = 0.50) for the highest vs second quintile of consumption
31) Ness AR (2005)The Boyd Orr Cohort83MortalityRR = 2.01 (1.09-3.69; P = 0.01)
29) Folsom AR (2004)The Iowa Women's Health Study313MortalityRR = 1.06 (0.67-1.67; P = 0.65)
27) Sauvaget C (2003)The Hiroshima/Nagasaki Life Span Study1,462MortalityHR = 0.85 (0.75-0.98; P = 0.02)
24) Mozaffarian D (2005)The Cardiovascular Health Study626RiskHR = 0.74 (0.54-1.02; P = 0.04)
23) Nagata C (2002)The Takayama Study137 men, and

132 women
MortalityMen: HR = 1.19 (0.78-1.81; P = 0.37).

Women: HR = 0.87 (0.58-1.30; P = 0.49).
22) Wennberg M (2007)The MONICA Study189 men, and

128 women
RiskMen: OR = 1.24 (1.01-1.51; P = 0.04).

Women: OR = 0.90 (0.73-1.12; P = 0.35).
19) Yuan JM (2001)The Shanghai Cohort Study480MortalityRR = 1.05 (0.77-1.43; P = 0.47)
17) Gillum RF (1996)The NHANES I262 white men,

251 white women,

107 black men and women
RiskWhite men: RR = 0.85 (0.49-1.46).

White women: RR = 0.55 (0.32-0.93; P = 0.05).

Black men and women: RR = 0.51 (0.30-0.88; P = < 0.05).
15) Morris MC (1995)The Physician's Health Study173RiskRR = 0.6 (0.3-1.6; P = 0.13)
14) He K (2002)The Health Professsional's Follow-up Study608RiskRR = 0.83 (0.53-1.29; P = 0.81)
14) Iso H (2001)The Nurses' Health Study574RiskRR = 0.48 (0.21-1.06; P = 0.06)
13) Montonen J (2009)The Finnish Mobile Clinic Health Survey659RiskRR = 1.01 (0.81-1.27; P = 0.80)
10) Kinjo Y (1999)No cohort name defined11,030MortalityRR = 0.86 (0.79-0.94)
6) Lapidus L (1986)No cohort name defined13RiskNo significant association
2) Orencia AJ (1996)The Western Electric Study222RiskHR = 1.26 (0.74-2.16)
1) Keli SO (1994)The Zutphen Study42RiskHR = 0.71 (0.38-1.33)
Total number of cases: 21,290Average RR = 0.87
Excluding data from Kinjo Y [10].Total number of cases: 10,260Average RR = 0.88


Prospective studies of total fish and ischemic stroke risk:
AuthorCohort nameCasesEnd pointRelative Risk (RR)
42) Larsson SC (2011)The Swedish Mammography Cohort1,310Cerebral infarction riskRR = 0.87 (0.73-1.04; P = 0.19)
36) Yamagishi K (2008)The JACC Study319Ischemic stroke mortalityHR = 0.93 (0.65-1.34; P = 0.78)
32) Nakamura Y (2005)The NIPPON DATA80165Cerebral infarction deathRR = 1.11 (0.50-2.47; P = 0.70) for the highest vs second quintile of consumption
27) Sauvaget C (2003)The Hiroshima/Nagasaki Life Span Study665Cerebral infarction mortalityHR = 0.94 (0.77-1.14; P = 0.50)
24) Mozaffarian D (2005)The Cardiovascular Health Study537Ischemic stroke riskHR = 0.70 (0.50-0.99; P = 0.02)
22) Wennberg M (2007)The MONICA Study147 men, and

111 women
Ischemic stroke riskMen: OR = 1.25 (1.00-1.56; P = 0.04).

Women: OR = 0.93 (0.74-1.17; P = 0.51).
14) He K (2002)The Health Professsional's Follow-up Study377Ischemic stroke riskRR = 0.54 (0.31-0.94; P = 0.28)
14) Iso H (2001)The Nurses' Health Study303Ischemic stroke riskRR = 0.38 (0.12-1.19; P = 0.09)
13) Montonen J (2009)The Finnish Mobile Clinic Health Survey364Thrombosis or embolia riskRR = 0.99 (0.73-1.35; P = 0.96)
10) Kinjo Y (1999)No cohort name defined4,084Embolism and thrombosis mortalityRR = 0.99 (0.86-1.14)
Total number of cases: 8,382Average RR = 0.91


Prospective studies of total fish and hemorrhagic stroke risk:
AuthorCohort nameCasesEnd pointRelative Risk (RR)
42) Larsson S (2011)The Swedish Mammography Cohort233Hemorrhagic stroke riskRR = 0.67 (0.42-1.08; P = 0.08)
36) Yamagishi K (2008)The JACC Study180 intraparenchymal hemorrhage, and

153 subarachnoid hemorrhage
MortalityIntraparenchymal hemorrhage: HR = 0.95 (0.62-1.47; P = 0.58).

Subarachnoid hemorrhage: HR = 0.96 (0.55-1.68; P = 0.84).
32) Nakamura Y (2005)The NIPPON DATA8063Cerebral hemorrhage deathRR = 0.93 (0.20-4.28; P = 0.97) for the highest vs second quintile of consumption
27) Sauvaget C (2003)The Hiroshima/Nagasaki Life Span Study354Intracerebral haemorrhage mortalityHR = 0.70 (0.54-0.92; P = 0.008)
24) Mozaffarian D (2005)The Cardiovascular Health Study73Hemorrhagic stroke riskHR = 0.93 (0.37-2.33; P = 0.66)
22) Wennberg M (2007)The MONICA Study39 men, and

15 women
Hemorrhagic stroke riskMen: OR = 1.14 (0.69-1.88; P = 0.59).

Women: OR = 0.61 (0.23-1.57; P = 0.31).
14) He K (2002)The Health Professsional's Follow-up Study106Hemorrhagic stroke riskRR = 1.55 (0.45-5.35; P = 0.70)
14) Iso H (2001)The Nurses' Health Study181Hemorrhagic stroke riskRR = 1.02 (0.34-3.10; P = 0.33)
13) Montonen J (2009)The Finnish Mobile Clinic Health Survey80Intracerebral haemorrhage riskRR = 1.23 (0.63-2.42; P = 0.41)
10) Kinjo Y (1999)No cohort name defined4,773Cerebral haemorrhage mortalityRR = 0.87 (0.76-0.98)
Total number of cases: 6,250Average RR = 0.89