Purpose:

Vegetarian diets have been associated with reduced risk of ischemic heart disease (IHD). However, results regarding cardiovascular disease (CVD) overall and stroke are less clear. We conducted a systematic review and meta-analysis of prospective cohort studies on CVD, IHD and stroke risk among vegetarians or vegans versus nonvegetarians to clarify these associations.
Methods:

PubMed and Ovid Embase databases were searched through August 12, 2021. Prospective cohort studies reporting adjusted relative risk (RR) estimates and 95% confidence intervals (CIs) for incidence or mortality from CVD, IHD and stroke, comparing vegetarians and vegans to nonvegetarians were included. Risk of bias (RoB) was assessed using ROBINS-I and the strength of evidence was assessed using World Cancer Research Fund (WCRF) criteria. Summary RRs (95% CIs) were estimated using a random effects model.
Results:

Thirteen cohort studies (844,175 participants, 115,392 CVD, 30,377 IHD, and 14,419 stroke cases) were included. The summary RR for vegetarians vs. nonvegetarians was 0.85 (95% CI: 0.79–0.92, I2 = 68%, n = 8) for CVD, 0.79 (95% CI: 0.71–0.88, I2 = 67%, n = 8) for IHD, 0.90 (95% CI: 0.77–1.05, I2 = 61%, n = 12) for total stroke, and for vegans vs. nonvegetarians was 0.82 (95% CI: 0.68–1.00, I2 = 0%, n = 6) for IHD. RoB was moderate (n = 8) to serious (n = 5). The associations between vegetarian diets and CVD and IHD were considered probably causal using WCRF criteria.
Conclusions:

Vegetarian diets are associated with reduced risk of CVD and IHD, but not stroke, but further studies are needed on stroke. These findings should be considered in dietary guidelines.