6afb5300_usation___HealthNewsReview_org__Study_design
Among women, higher consumption of fish is associated with a lower risk of coronary heart disease (CHD), particularly CHD deaths Women who ate fish 5 times a week cut their risk of dying later from a heart attack by half [Problem] Cut their risk of dying is causal. [Suggested language] Compared to women who rarely ate fish, those who ate fish regularly had less heart disease and related death. But, this type of study, which just observes people, rather than randomly assigning them to eat fish or not, cannot prove that fish consumption had a protective effect. [Study design] 
Prospective cohort study of fish intake and coronary heart disease in women (Nurses’ Health Study; observational)
Observational Studies - Does The Language Fit The Evidence? - Association Versus Causation - HealthNewsReview.org
Study design